Researchers at Baylor University are working on adapting lithophanes—an ancient artistic medium—for modern efforts to make scientific images accessible and understandable via touch. Lithophanes, which are thin, detailed engravings made from translucent materials, are thought to have originated in China as early as the seventh century and rose in popularity in Europe in the 1800s. The new lithophanes from the Baylor researchers are the first known examples of their kind and are intended for use as tactile learning tools for blind and visually impaired individuals. The new lithophanes can enable sightless or low-vision individuals to visualize microscopic and nanoscopic structures—for instance, in the subjects of anatomy and chemistry—with a greater level of detail and retainability than previously possible—and even at the same "resolution" as that of sighted individuals. See also: Learning; Visual impairment

Using traditional welding methods, rocket engine nozzles and combustion chambers are some of the most difficult parts to fabricate, requiring up to a year to produce a single part. Now, however, the U.S. National Aeronautics and Space Administration (NASA) is using additive manufacturing technology, also known as 3D printing, to additively build those parts, layer upon layer. This technology differs completely from traditional manufacturing methods that manufacture destructively by taking away material until a final geometry is realized. 3D printing has allowed NASA to produce rocket engine nozzles with integrated cooling channels in 30 days by way of an additive process called blown powder directed energy deposition (BP-DED). See also: Nozzle; Rocket propulsion; 3D printing

3D printing, also known as stereo modeling or rapid prototyping, starts with a computer-aided design (CAD) [digital drawing] file of an object. The CAD file is then converted to a 3D printer file, which represents the object in layers and directs the printer to deposit layer upon layer of material to build an object from bottom to top. See also: Computer-aided design and manufacturing

Cosmochemists have discovered the oldest solid material known to exist on Earth. The material, stardust, consists of silicon carbide grains measuring around one micrometer in size. The grains date back approximately 7 billion years, or about 2.5 billion years before the Sun and solar system formed. Aged stars nearing the end of their life cycles originally forged the grains, which then were captured inside a meteorite that formed around 4.6 billion years ago, eventually crashing into Australia in 1969. Analyzing the dust will help scientists study previous stellar generations in our galaxy. See also: Milky Way Galaxy; Star; Sun

On July 20, 1969, the bulkily space-suited figure of astronaut Neil Armstrong descended the ladder of Apollo 11’s lunar lander, planted his boot in the Moon's gray dust, and declared: "That's one small step for a man, one giant leap for mankind." This first visit to Earth's natural satellite—the culmination of NASA's Apollo 11 mission—was a seminal moment in the history of human space exploration (Fig. 1). See also: Moon; Space flight

On April 29, 2015, the U.S. Geological Survey (USGS) reported five earthquakes in Oklahoma of magnitude 2.5 or greater—that is, tremors strong enough to be felt. The most powerful of these was a M4.1 earthquake 21 km (13 mi) west of the city of Perry in north-central Oklahoma. Based on recent evidence reported by the USGS, these earthquakes were almost certainly induced by human activity as a consequence of the injection of wastewater from oil and gas production into deep disposal wells. See also: Earthquake; Oil and gas field exploitation; Well

On April 25, 2015 at 11:56 a.m local time, a magnitude 7.8 earthquake struck in the district of Lamjung, approximately 80 km northwest of Kathmandu, Nepal. The earthquake, now known as the Gorkha quake, occurred as the result of thrust faulting [15.0 km (9.3 mi) in depth] in the region where the India plate is sinking (subducting) beneath the Eurasia plate, according to the United States Geological Survey (USGS). Damage to buildings was extensive and over 8700 people were killed. See also: Earthquake; Fault and fault structures; Subduction zones

A magnitude 5.1 nuclear test was detected 376 km (234 mi) NE of Pyongyang, North Korea (DPRK) on January 6, 2015 at 10:30 a.m. local time (01:30 UTC), according to the U.S. Geological Survey (USGS). The event was picked up at seismic stations around the world. The Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO) said that the explosion occurred in roughly the same area as North Korea’s previous nuclear test on February 12, 2013. See also: Nuclear explosion; Nuclear testing; Seismographic instrumentation

The Ebola virus comprises a group of pathogenic agents that cause severe and deadly hemorrhagic fevers in humans and other primates. During 2014 and 2015, an Ebola virus epidemic in West Africa—predominantly, the countries of Guinea, Liberia, and Sierra Leone—killed more than 11,300 people; it was the worst outbreak of this disease in recorded human history. At that time, the World Health Organization (WHO) declared the Ebola outbreak to be a Public Health Emergency of International Concern (PHEIC), and massive efforts were undertaken to contain the spread of the deadly disease. By early 2016, the affected countries were declared free of Ebola virus transmission, and the epidemic was considered to have ended. However, since then, isolated outbreaks have occurred sporadically, mostly as a result of the virus persisting in survivors after recovery. Most troublesome, though, the Ebola virus was detected in August 2018 in the Democratic Republic of the Congo (DRC) in Central Africa and has since expanded dramatically. It is now the second-largest Ebola outbreak on record. As of June 2019, more than 2000 Ebola cases have been detected, with more than 1350 resultant deaths. See also: Africa; Ebola virus; Ebola virus outbreak in 2014–2015; Exotic viral diseases; Infectious disease; Virus

The United Nations has proclaimed 2019 the International Year of the Periodic Table of Chemical Elements (IYPT2019). The same year also marks the 150th anniversary of the publication of Russian chemist Dmitri Mendeleev’s periodic table, containing 63 elements, in which the known elements were arranged horizontally by their atomic weight and vertically in groups of elements with similar "periodic" properties. The present periodic table, containing 118 elements, is completely filled. It includes element 101 named mendelevium (Md). According the United Nations, the purpose of this commemoration of the periodic table is, “to enhance global awareness of and education in the basic sciences.” A number of IYPT2019 special events have been planned. See also: Atomic mass; Mendelevium; Periodic table

Wildfires are a natural phenomenon in many ecosystems, including forests along the U.S. Pacific West Coast, as natural fires serve to rejuvenate ecological communities. However, from mid-August through mid-September 2020, forests in California, Oregon, and Washington State suffered through unprecedented wildfires caused by extreme weather events that can be attributed to climate change. By September 15, 2020, in Washington state, 700,000 acres (280,000 hectares) had burned; in Oregon, about 1 million acres (405,000 hectares) had burned; and in California, the worst-hit state, more than 7700 fires had burned 3 million acres (1.2 million hectares), damaged or destroyed more than 5000 structures, and killed at least 35 people. The single largest fire to date was the California Complex fire in Northern California, which was still raging on September 15 after it had already burned about 800,000 acres (320,000 hectares). These epic blazes have created some of the worst air pollution in the world from Seattle, Washington, to Southern California, with haze reaching as far east as New York City. See also: Air pollution; Extreme weather events; Forest fire; Global climate change; Wildfire impact on air quality

Active traffic management (ATM) uses advanced technologies (computing, communication, and electronics) and traffic management centers to improve roadway traffic flow. Adaptive traffic signal control is an ATM solution for reducing traffic congestion through intersection signal (traffic light) optimization using real-time data. The essential components of the control system are roadside traffic sensors, a central computer (control center), traffic-signal controllers at the intersections, and a fiber-optic or wireless communication system. In recent years, Los Angeles and New York City have made significant investments in upgrading their traffic signals to adaptive control. See also: Active traffic management; Data communications; Highway engineering; Optimal control theory; Optimization; Traffic-control systems; Ubiquitous transportation network sensors

The Joshua tree (Yucca brevifolia) is a remarkable evergreen, treelike plant found only in the southwestern United States. It was named by Mormon settlers in the early 1800s. Upon seeing the limbs of this plant branching upwards to heaven, the Mormon travelers were reminded of the biblical prophet Joshua, who raised his arms in prayer for guidance to the Promised Land. The Joshua tree is the largest member of the Yucca genus of monocotyledonous trees and shrubs, which is placed in the agave family (Agavaceae; order Asparagales) or the lily family (Liliaceae; order Liliales), depending on the taxonomic system being used for classification. The height of the Joshua tree can reach 15 to 40 feet (4.6 to 12.2 meters) and its diameter ranges from 1 to 3 feet (0.3 to 0.9 meters). Life spans of 150 to 200 years have been documented for this resilient species, with some unverified ages of 500 to 1000 years being estimated. See also: Asparagales; Liliales; Monocotyledons; Tree

There is a growing body of evidence that many of the thousands of prescription and over-the-counter medications ultimately make their way into water bodies and drinking-water supplies. Typical wastewater treatment plants may not be effective at removing pharmaceuticals. This is because there are no regulations limiting the release of these substances in the environment and, as a result, the needed treatment technology may not have been investigated or implemented. Knowing the best treatment practices for removing pharmaceuticals from wastewater is important for protecting drinking-water supplies as well as organisms in marine and aquatic environments because many pharmaceuticals are designed to be effective at low concentrations. A new study shows that removal of pharmaceuticals from wastewater is possible, even at very low concentrations, depending on the specific treatment process, according to researchers reporting in Environmental Science: Water Research & Technology (January 2020). See also: Environmental toxicology; Freshwater ecosystem; Marine ecology; Water pollution; Water resources; Water treatment

As social animals, humans tend to form groups that can range in size from a few individual members to entire nation-states. Historically and through the present day, human groups frequently come into conflict. A noted feature of human intergroup conflict is the proclivity of ingroup members—that is, members recognized as being part of a particular group—to inflict harm upon those considered to be non-members who are part of an outgroup. A new study may help explain the motivation for this hostility. The study found that aggression directed at rival group members increases activity in certain brain regions that are associated with feelings of reward and pleasure. Investigating this potential link further could deepen our understanding of the origins of intergroup aggressiveness and suggest interventions for curbing group-based violence. See also: Aggression; Brain; Motivation; Sociobiology

Microplastics are raining down on national parks and other protected areas in the western United States at the rate of about 132 pieces of microplastic per square meter every day, according to a report in the journal Science (June 2020). Microplastics are plastic particles measuring less than five millimeters (approximately 0.2 inches) in length. The reported precipitation rate is similar to dumping about 300 million pulverized plastic water bottles (about 1000 tons) over the studied areas each year. Where do these particles come from? Sources mostly include fragments from virgin plastic pellets, polymer textile fibers, microbeads from personal care products and spray paints, as well as environmental degradation of waste plastic into smaller and smaller pieces over time. See also: Manufactured fiber; Paint and coatings; Plastic waste pollution; Polymer; Textile

The benefits of outdoor physical activity (exercise) outweigh the potential harm caused by air pollution except in the most highly polluted cities, according to epidemiological studies reported in the journal Preventive Medicine (February 2016). Exercise provides a number of health benefits, including reduced risks of cardiovascular disease, type 2 diabetes, and some cancers. Cycling and walking, for example, offer not just health benefits but also environmental advantages as pollution-free means of transportation. See also: Air pollution; Cancer (medicine); Epidemiology; Heart disorders; Sports medicine; Type 2 diabetes

A research group at the European Organization for Nuclear Research (CERN) has performed the first-ever high-precision measurement of the gravitational weight of antimatter, a rare substance that appears identical to ordinary matter in all properties except for electric charge. As described in a recent paper, antimatter experiences the same amount of gravitational attraction on Earth as ordinary matter, at least up to the precision limits available in ALPHA-g, the experiment that produced the results. The finding offers new insights into the physical nature of antimatter. See also: Antimatter; Earth's gravity field; Electric charge; Matter; Weight (physics)

Advances in aluminum-air battery technology might allow electrically powered vehicles to become more realistic and competitive automotive options for many drivers.

The species diversity and ultimate survival of amphibians, one of the major groupings of vertebrate animals, face tremendous challenges today for reasons that are still not entirely understood. Since the 1980s, the pace of amphibian extinction has been alarming, and almost 200 identified species have become extinct. About one-third of all amphibian species have seen dramatic declines in populations, and are now considered to be endangered or threatened with extinction. See also: Biodiversity; Endangered species; Extinction (biology); Extinction of species

Collectively, members of the class Amphibia are facing massive reductions in total numbers, and the overall biodiversity of amphibians across the globe is under threat. Scientists have determined that global climate change and habitat destruction are two chief factors responsible for some of the decreases observed in amphibian populations. However, another prime culprit has been discovered—specifically, chytridiomycosis. Chytridiomycosis is a disease caused by the waterborne fungal pathogen Batrachochytrium dendrobatidis (abbreviated as Bd). Since the 1980s, scientists have linked the chytrid fungus to the significant loss of much amphibian biodiversity in many locations around the world. More than 500 amphibian species have suffered total number losses as a result of chytridiomycosis, with at least 90 of these species becoming extinct. In addition, 124 species have suffered a 90% reduction in their populations, endangering their continued existence. Although all amphibian species are thought to be susceptible to chytridiomycosis, frogs and toads (order Anura) have been affected to the greatest degree. See also: Amphibia; Anura; Biodiversity; Endangered species; Extinction; Fungi; Global climate change; Mycology; Origins of modern amphibians

The ancient Egyptian civilization flourished along the banks of the Nile River, which supplied the waters that ensured a prosperous and lengthy agricultural vitality over the course of thousands of years. On the strength provided by this rich agricultural productivity, the Egyptian civilization was able to develop into one of the foremost and notable ancient empires, excelling in architecture (including the use of the ramp and the lever in construction), science, medicine (including the art of mummification), mathematics, writing (hieroglyphic script), art, engineering, stone masonry, irrigation techniques, and commerce. See also: Africa; Agricultural science (animal); Agricultural science (plant); Agriculture; Anthropology; Archeology; Architectural engineering; Inclined plane; Irrigation (agriculture); Lever; Masonry; Mathematics; Medicine; River; River engineering; Science; Scientific methods; Stone and stone products

Sea-level rise is caused by adding mass (water) and heat to the ocean. The Antarctic ice sheet represents a potentially large source of water. Knowing the speed and direction (velocity) at which the Antarctic ice sheet is flowing to the ocean is important for assessing current and future sea-level rise. Scientists from the University of California, Irvine, and the NASA Jet Propulsion Laboratory have published the most precise map ever of Antarctic ice velocity in the journal Geophysical Research Letters (July 2019). The new map will be useful for mass-balance and ice-thickness studies of the Antarctic ice sheet as well as for modeling climate and sea-level rise. Compared to earlier maps, the new map is 10 times more accurate in terms of ice-flow direction and speed and shows ice movement over 80 percent of Antarctica versus 20 percent shown in past maps. See also: Antarctica; Climate modeling; Glaciology; Global climate change; Sea-level rise

In 1987, the Montreal Protocol, the international treaty banning chemicals that deplete the ozone layer, was adopted. Thirty years later, NASA scientists reported in the journal Geophysical Research Letters (January 2018) satellite measurements showing decreased stratospheric ozone depletion as a result of declining levels of ozone-depleting chlorine from the breakdown of chlorofluorocarbons (CFCs)—that is, chemicals that were used as solvents, refrigerants, and aerosol-can propellants. The ozone hole is an area of severely depleted ozone in the stratosphere over Antacrtica, appearing at the beginning of Southern Hemisphere spring (August–October). From 2005 to 2016, instruments aboard the NASA Aura satellite measured chlorine and ozone levels in the Antarctic ozone hole. As compared to measurements taken in 2005, the measurements showed about a 20 percent decline in ozone depletion during the Antarctic winter. This is the first study to confirm that the ozone hole has begun healing and that the recovery can be attributed to the implementation of the Montreal Protocol. See also: Antarctica; Halogenated hydrocarbon; Ozone; Stratosphere; Stratospheric ozone

Researchers have developed polymeric materials that are able to kill multidrug-resistant bacteria without inducing drug resistance or toxic side effects, according to a report in Nature Communications (March 2018). The polymers, known as guanidinium-functionalized polycarbonates, contain a polycarbonate backbone to which a hydrophobic spacer group carrying a guanidinium C(NH₂)₃⁺ group is attached. The positively charged guanidinium group enables the polymer to be prepared as a water-soluble salt as well as to bind to the negatively charged cell walls of bacteria. After attachment, the polymer penetrates and crosses the cell membrane and then precipitates the proteins and genes in the cytoplasm, effectively killing the bacteria. Antibiotic resistance in bacteria is a serious problem worldwide, with the World Health Organization in January 2018 reporting 500,000 people with suspected antibiotic-resistant infections in 22 countries. See also: Antibiotic; Antibiotic resistance; Antimicrobial agents; Drug resistance; Infectious disease; Polymer

It is estimated that 1 gram of soil can be inhabited by up to 10⁹ microorganisms and approximately 60,000 bacterial species. Moreover, soil harbors a vast reservoir of antimicrobial agents, and soil-dwelling bacteria have played a key role in the introduction of antibiotics to treat infectious diseases. Because these resilient bacteria not only produce antibiotics but also are exposed to other antibiotics produced by surrounding strains in the soil, they have developed diverse mechanisms to survive the toxic antimicrobial compounds created around them. Importantly, these mechanisms of robust resistance to numerous classes of antibiotics often resemble the mechanisms of resistance identified in clinical pathogens, including those that infect humans. Thus, scientists are attempting to find possible correlations between antibiotic resistance in soil bacteria and in infectious agents in humans. If correlations can be found, investigators might be able to predict future signs of clinical resistance to certain antibiotics, providing clinicians with methods to circumvent any potential resistance that may emerge. See also: Antibiotic; Antimicrobial agents; Antimicrobial resistance; Bacteria; Clinical microbiology; Drug resistance; Infectious disease; Medical bacteriology; Microbiology; Pathogen; Soil; Soil microbiology

Antisense drugs are gene-based molecules that inhibit the synthesis of proteins (including proteins that cause specific diseases) by binding to the ribonucleic acids (RNAs) responsible for their formation. Specifically, these drugs are single-stranded short polymers of RNA or deoxyribonucleic acid (DNA), termed oligonucleotides, designed to contain part of the noncoding strand of messenger RNA (mRNA), which is a molecule involved in translating DNA into protein. Antisense medications are therefore capable of hybridizing with and inactivating the mRNA, preventing the associated gene from producing the unwanted protein. With their anticancer, antiviral, and anti-inflammatory therapeutic capacities, these drugs have been applied in the treatment of various genetic disorders and infections, including diabetes, rheumatoid arthritis, cytomegalovirus retinitis (a virally caused form of blindness that occurs often in AIDS patients), asthma, hypercholesterolemia (a genetic derangement of fat metabolism characterized by very high levels of cholesterol in the blood), and numerous cancers. Research is also being conducted on patients suffering from Parkinson's disease and Huntington's disease to determine whether antisense therapy can mitigate the effects of these conditions. See also: Biotechnology; Deoxyribonucleic acid (DNA); Disease; Gene; Genetic engineering; Oligonucleotide; Protein; Ribonucleic acid (RNA)

A powerful magnitude 7.8 earthquake struck Ecuador on April 16, 2016 at 6:58 p.m. local time, causing extensive damage to buildings and infrastructure as well as hundreds of fatalities and thousands of injuries. The epicenter was located 52.0 km (32.3 mi) west of Rosa Zarate. The earthquake occurred as the result of thrust faulting 19.2 km (11.9 mi) in depth near the boundary of the Nazca and Pacific plates, according to the U.S. Geological Survey (USGS). See also: Earthquake; Fault and fault structures; Subduction zones

To bolster food security in a warming world, engineers are developing a coating that could better protect seeds, such as beans, from drought in semiarid regions. The coating mimics a mucilage-based hydrogel produced naturally by some seeds, such as basil and chia. The hydrogel traps moisture, regulates nutrient retention, and creates an environment around the seed which promotes the growth of beneficial microorganisms. The artificial coating is accordingly tailored to help protect seeds during germination and early seedling growth. In semiarid regions, water stress caused by a lack of available moisture during these sensitive periods of a plant's development is the highest cause of crop loss worldwide. This water stress on agricultural crops in drought-prone, marginal lands is expected to substantially increase in coming decades because of global climate change. See also: Agricultural engineering; Drought; Farm crops; Global climate change; Mucilage; Seed

Soil harbors a vast reservoir of antimicrobial agents. In fact, approximately 80% of all clinically implemented antibiotics are derived from soil-dwelling bacteria. However, many bacteria have evolved methods to evade the effects of various antibiotics and thus have acquired resistance to these chemical substances. Today, the increasing resistance of many common disease-causing bacteria to antibiotics is a global health crisis. Therefore, scientists are seeking to develop new antibiotics that can overcome the resistance capabilities of numerous pathogenic bacteria. Arylomycins are considered to be among the most promising of these new compounds. See also: Antibiotic; Antibiotic resistance; Antibiotic resistance in soil bacteria; Antimicrobial agents; Bacteria; Infectious disease; Medical bacteriology; Microbiology; Pathogen; Public health; Soil; Soil microbiology

The Asian longhorned tick (Haemaphysalis longicornis), also known as the bush tick, is a troublesome parasitic species and is an important vector of disease agents. (Note that vectors are capable of biologically transferring a pathogen from one organism to another.) It also is becoming a problematic invasive species. Specifically, it is invading areas located far from its native region in East and Central Asia and is spreading within the United States. In particular, this arachnid is remarkable because female members can reproduce asexually without mating. Thus, scientists fear that the species will spread rapidly in locations where it has already invaded, thereby transmitting numerous diseases that are potentially harmful to humans and other animals. See also: Acari; Disease; Invasive species; Ixodides; Parasitology; Pathogen; Tick virus diseases; Zoonoses

Although asphalt (also known as bitumen) is a naturally occurring substance found in deposits within the earth, it is also a by-product of petroleum processing. Almost all the bitumen used for asphalt pavement and roofs comes from petroleum refining and consists of hydrocarbon compounds that remain at the upper end (600°C or 1100°F) of the vacuum-distillation process. Because asphalt cannot be vacuum distilled, it has long been assumed that installed asphalt pavement and roofs do not emit hydrocarbon pollutants. Yet, according to a new report in the journal Science Advances (September 2020), asphalt pavements and roofs do, in fact, emit significant quantities of hydrocarbons, including polycyclic aromatic hydrocarbons (PAHs), particularly in environmental conditions found on hot and sunny days. This is problematic, because some PAHs are mutagens, teratogens, carcinogens, or endocrine disruptors and therefore harmful to human health and the environment. Hydrocarbons may also act as precursors to air pollutants, because hydrocarbons can react with nitrogen oxides (NO_x) and sunlight to form ozone, a major constituent of smog. See also: Air pollution; Aromatic hydrocarbon; Asphalt and asphaltite; Environmental toxicology; Nitrogen oxides; Ozone; Pavement; Petroleum; Petroleum processing and refining; Petroleum products; Roof construction; Smog

In September 2020, researchers answered a longstanding question about why planetary nebulae display such a rich variety of shapes. Winds from aging stars produce planetary nebulae as the winds eject the stars' outer layers, shrouding the stars in stellar material. Views through early telescopes made this ejected material appear rounded and planet-like. As telescope technology improved, however, astronomers came to realize that planetary nebulae can look like flowers and butterflies, among other varied, asymmetrical shapes. Those shapes confounded astronomers, given their assumption that stellar winds are spherical in nature, similar to stars themselves, and should thus produce only rounded nebulae. The September 2020 study revealed, however, that these winds actually blow asymmetrically. Furthermore, as winds throw material off the star unevenly, stellar companions—such as other stars and planets—can scramble the material, rather like a spoon stirring creamer in hot coffee. Overall, these effects combine to produce the observed diversity of nebular forms. See also: Nebula; Planet; Planetary nebula; Star; Telescope; Wind

On August 5, 2018 at 6:46 p.m. local time, a magnitude 6.9 earthquake struck in Pulau Lombok, Indonesia. The earthquake occurred as the result of thrust faulting at a depth of 10.5 km (6.5 mi) in northern Lombok, according to the United States Geological Survey (USGS). A tsunami warning was issued, but was lifted after only small waves were recorded. Early reports stated that 98 people were killed and more than 200 injured, as the earthquake caused many buildings to collapse. Some structures that collapsed had already been damaged one week earlier (June 29, 2018) when a magnitude 6.4 earthquake struck Lombok, killing 17 people and injuring more than 160. Indonesia is located in a very seismically active zone, in which magnitude 5.0 or greater earthquakes were recorded on 17 of 31 days in July 2018. See also: Earthquake; Earthquake engineering; Fault and fault structures; Seismology; Tsunami

Wildfires, also termed bushfires or forest fires, are currently devastating large swaths of land in Australia. Detrimental ecologic consequences of these uncontrolled combustions of forest fuels and vegetation are numerous. One of the most serious issues pertains to the survival of the koala, which is a small marsupial (pouch-bearing mammal) found only on that continent. Conservationists and scientists are concerned that the hundreds of fires presently raging in Australia, which were brought about by hotter and drier conditions exacerbated by anthropogenic climate change, may cause significant enough reductions in the population of koalas to threaten the continued existence of this species. See also: Australia; Forest fire; Global climate change; Global warming; Koala; Marsupialia

The Aztecs were an indigenous group of Mesoamerican tribal peoples whose influence dominated that region between the fourteenth and early sixteenth centuries. They predominantly spoke a native language called Nahuatl, and they lived a nomadic existence prior to the twelfth century. See also: Agricultural science (plant); Agriculture; Bean; Corn; Domestication (anthropology); North America

The Babylonian civilization flourished from approximately 1900 to 539 BC in the central and southern regions of Mesopotamia (present-day Iraq), predominantly between the Euphrates and Tigris rivers. Before the rise of the Babylonians, the area was inhabited by the Sumerians in southeast Mesopotamia and the Akkadians in northwest Mesopotamia. Through a series of expansions and conquests undertaken by various dynastic kings, these two cultures were incorporated into the Babylonian empire, which eventually established control over many other kingdoms from ancient Persia to Syria and Palestine. Along with this political and geographical dominance, the cities of the Babylonian empire became rich centers of learning, especially in the areas of astronomy, astrology (including the division of the night sky into a zodiac of constellations), mathematics, and medicine. The most important city was Babylon, which was situated 88 kilometers (55 miles) southwest of modern-day Baghdad. Once famous for its impressive architectural marvels, including massive walls, ziggurats (pyramid-shaped temples built on platforms), and the Hanging Gardens of Babylon (considered to be one of the Seven Wonders of the Ancient World), few remains of this ancient city can be found today. In addition, it is likely that the biblical story of the Tower of Babel was based on an ancient Babylonian structure. See also: Anthropology; Archeoastronomy; Archeology; Architectural engineering; Astronomy; Mathematics; Medicine; Science; Scientific methods; Zodiac

Recycling or reuse is in most instances environmentally preferable to disposal. Reuse of coal tar as an asphalt-pavement sealant for driveways and parking lots, however, has turned out to be an exception to this rule of thumb. See also: Asphalt and asphaltite; Pavement

Bats are members of the order Chiroptera, which is the second-largest order of living mammals. The geographic distribution of these flying mammals is tremendous as well, ranging from the limit of trees in the Northern Hemisphere to the southern tips of Africa, South America, and New Zealand. Within such a wide distribution, bats frequently encounter human populations. However, close contact between bats and humans is problematic with regard to disease ecology and epidemiology because bats are natural reservoirs (primary hosts) or intermediate hosts for numerous zoonotic pathogens—that is, infectious disease agents that are transmitted from animals to humans. Specifically, bats harbor more than 60 pathogenic viruses that can infect humans, including Ebola, Marburg, Nipah, Hendra, and rabies viruses. Bats also harbor various coronaviruses, including those responsible for severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and coronavirus disease 2019 (COVID-19). See also: Chiroptera; Coronavirus; Disease ecology; Epidemiology; Exotic viral diseases; Infectious disease; Mammalia; Pathogen; Rabies; Virus; Zoonoses

The American beech (Fagus grandifolia) is native to forest regions east of the Mississippi River and is a key tree species in the United States. In particular, it is very abundant from Ohio to the New England states. The tree is also found in the southernmost portions of eastern Canada, especially southern Ontario. Since 2012, though, American beech trees have been distressed by a lethal leaf disease—termed beech leaf disease—that has spread rapidly from Ohio into the other aforementioned geographical areas. Most cases of the disease have been detected in forest regions, but landscaped locations also have been affected. The external symptoms of the disease include striped banding and shriveling of tree leaves, aborted budding, reduced production of leaves, and premature leaf drop. More importantly, beech trees with beech leaf disease often die within a relatively short span of time after being inflicted by the disease—within 2 to 3 years for saplings and within 6 years for larger and older trees. See also: Beech; Forest; Forestry; Leaf; Tree; Tree diseases

The dance language of honeybees (Apis mellifera) is a unique form of animal behavior and communication that was discovered by the zoologist Karl von Frisch (1886–1982) in the 1920s, which he continued to study through the 1960s and for which he was awarded a Nobel Prize in 1973. When foraging worker honeybees return to the hive with pollen or nectar, they perform dance movements to recruit other bees (follower bees) to visit a food source. The specifics of these movements convey information about the distance and direction from the hive to the food. This type of communication is highly unusual: Nonhuman animal communication typically concerns conditions and events immediately surrounding the instigator, whereas the honeybee dance language transmits information about remote events [scientists have documented bee dances about food sources up to 15 kilometers (9.3 miles) away from hives]. See also: Animal communication; Beekeeping; Ethology; Hymenoptera; Pollen; Pollination; Social insects

Tardigrades, also known as water bears, are hardy eight-legged microorganisms ranging in length from 0.5 millimeters to 1.5 millimeters. Well known in the animal kingdom for their resilience in the face of extreme environments, tardigrades have survived in boiling water, deep sea trenches, and even space. Although the threshold of harsh conditions that tardigrades can withstand has been heavily studied, less understood is the biological mechanisms behind this unique tardigrade tolerance. See also: Astrobiology; Deep-sea trench; Space; Space biology; Tardigrada

Biocontrol, or biological control, is the natural or applied regulation of populations of pest organisms—especially insects—through the role or use of natural enemies. In other words, biocontrol uses living organisms to reduce and eliminate pest abundance and damage. The agents through which biocontrol is accomplished are varied. For example, biocontrol agents can be consumers of pests; thus, herbivores are used to reduce weeds, whereas predators or parasites are employed to diminish the number of insect and other animal pests. In addition, pathogens and competitors that interact with pests are often utilized in biocontrol. Typically, agricultural and forest pests are the major targets of biocontrol. Notably, biocontrol operates as an alternative to the use of pesticides that may be harmful to the environment. See also: Agricultural science (animal); Agricultural science (plant); Agricultural soil and crop practices; Agriculture; Biological insect control; Forest; Forestry; Insecta; Parasitology; Pathogen; Predator-prey interactions; Weeds

Biodegradable metals, also known as bioresorbable or bioabsorbable metals, are compatible with human tissues and degrade to nontoxic by-products. The most promising candidates for use as orthopedic and cardiovascular implants are alloys of magnesium, which biodegrade in 6–15 months, and alloys of iron, which biodegrade in 12–36 months. Both types of alloy degrade by corrosion—the oxidation and dissolution of the metals. See also: Alloy; Corrosion; Iron; Iron alloys; Magnesium; Magnesium alloys

For over fifty years, heat stabilizers, light stabilizers, and antioxidants have been added to polymers to maintain their material properties by preventing their degradation. This chemical adjustment is necessary to extend the life of products such as plastic pipes, paints and coatings, and automotive parts. More recently, additives with the opposite purpose have become available: They are designed to enhance the biodegradation of hydrocarbon polymers used in common products such as plastic bags. Biodegradation is the breakdown of organic compounds by microorganisms or other biological means to their inorganic mineral constituents, such as carbon dioxide (CO₂). Biodegradation additives would seem to be an elegant solution to the mounting environmental problem of plastic waste—except that recent research indicates they do not work. See also: Antioxidant; Biodegradation; Microbial ecology; Polymer; Polyolefin resins; Stabilizer (chemistry)

Many questions concerning the sustainable production of biofuels have emerged over recent years in terms of land and water use, pollution from fertilizer and pest-control chemicals, greenhouse-gas production, net energy production, and whether enhanced land-use and climate benefits would result from simply planting trees and eschewing biofuels altogether. According to researchers reporting in the Proceedings of the National Academy of Sciences (September 2020), the answer depends, in part, on optimizing land-use policies and bioenergy production systems. Researchers have concluded that sustainable biofuels could make an important contribution toward reducing greenhouse-gas emissions and stabilizing the global climate if we produce bioethanol from biomass sources, such as perennial grasses, that are grown without affecting the carbon already stored in the ecosystem. See also: Biomass; Ethyl alcohol; Global climate change; Greenhouse effect; Land-use planning; Reforestation

Humans have used dried bovine dung (manure) as a fuel source since prehistoric times. In India, for example, many people burn cow or buffalo dung for cooking fuel. This bioresource provides a low-cost fuel as well as an efficient means of waste disposal. However, in rural India, the burning of dung is simultaneously a source of hazardous indoor and outdoor air pollution, resulting from the emission of fine particulates that are 2.5 micrometers or less in diameter (PM_2.5). Such combustion byproducts are considered the most dangerous to human health, because PM_2.5 can be inhaled deep into the lungs, impairing lung function as well as and affecting other organs, such as the heart and brain, or causing cancer. See also: Air pollution; Indoor air pollution

Biologic drugs, also known as biologics or biologicals, are produced using living organisms. Various classic biologics, such as the medical human insulin taken by diabetics, have been made by biotechnology processes for some decades. What is relatively new are therapeutic biologics to treat autoimmune diseases and cancer, such as the trade-named monoclonal antibody drugs Remicade (infliximab) and Rituxan (rituximab) used to treat autoimmune diseases. See also: Antibody; Autoimmunity; Biologicals; Biotechnology; Molecular biology; Monoclonal antibodies

Although cats are the number one lethal threat to birds, collisions with building glass are not far behind. The number of birds killed each year by glass collisions worldwide is estimated to be in the billons. In the United States, the U.S. Fish & Wildlife Service estimates that between 400 million and one billion birds die each year from collisions with buildings. In contrast, an annual average of only 250,000 bird deaths result from collisions with land-based wind turbines. See also: Aves; Building; Glass; Wind power

Researchers recently discovered a black hole with a mass estimated at 3.3 times the mass of the Sun, which is significantly less than the lowest-mass black holes previously detected with approximately 5 times the Sun's mass. The new finding opens the door to the possibility that a sizable population of similarly low-mass versions of black holes has thus far escaped detection. Finding more members of this hypothetical population will help scientists better understand the origin and evolution of black holes, which are among the most extreme and enigmatic objects in the universe. See also: Black hole; Mass; Sun; Universe

Since its landing in 2012, NASA’s Curiosity rover has been analyzing Martian soils and rocks for evidence that the Red Planet could have supported life in its past. So far, Curiosity has found carbon, hydrogen, oxygen, phosphorus, sulfur, methane, and organic molecules. In addition, Curiosity has found evidence of surface water and groundwater. All these discoveries suggest favorable chemistry and conditions for supporting life, although not evidence of life. Most recently, scientists reported in the journal Geophysical Research Letters (September 2017) the discovery of the element boron, which may have acted as a stabilizer for the molecular precursors of life. See also: Boron; Mars Science Laboratory; Robot rover Curiosity lands on Mars; Prebiotic organic synthesis; Space probe

A group of researchers from Harvard University and the Massachusetts Institute of Technology in the United States, and Carleton University in Canada have jointly investigated how the human brain processes learning multiple languages. The team found that the way our brains process our first language is different than every subsequent language learned. Polyglots—people who speak several languages—were the focus of this study. Participants were recruited based on linguistic ability, with each individual reporting varying levels of proficiency in at least five languages and that they had not been multilingual from infancy. Thirty-four people were selected, of which 16 spoke ten or more languages, including one study participant who claimed to speak 54 languages to at least some degree. The human brain's language processing capabilities are located primarily in the frontal and temporal lobes of the left hemisphere. These areas of each participant's brain were scanned using functional magnetic resonance imaging, or fMRI, as the participants listened to read-aloud text samples in eight different languages. See also: Brain; Linguistics

In the historical development of spectroscopy, following the fundamental studies of crude spectra of sunlight by Isaac Newton in 1672, certain contributions and achievements are especially noteworthy. The significance of using a narrow slit instead of a pinhole or round aperture to produce spectra lines, each one an image of the slit and representing a different color or wavelength, was demonstrated independently by W. H. Wollaston in 1802 and by Joseph Fraunhofer in 1814. Fraunhofer made many subsequent contributions to optics and spectroscopy, including first observation of stellar spectra, discovery and construction of transmission diffraction gratings, first accurate measurements of wavelengths of the dark lines in the solar spectrum, and invention of the achromatic telescope. The origin of the dark Fraunhofer lines in the solar spectrum was accounted for by G. R. Kirchhoff in 1859 on the basis of absorption by the elements in the cooler Sun's atmosphere of the continuous spectrum emitted by the hotter interior of the Sun. See also: Astronomical spectroscopy; Diffraction grating; Fraunhofer lines; Spectroscopy; Spectrum; Sun

Although sales will continue for as long as inventory remains, worldwide production of incandescent lights (lamps) has mostly been phased out by the push for more energy-efficient lighting and improvements in light-emitting diodes (LEDs) and compact fluorescent lamps (CFLs). Between 2009 and 2015 the price of an LED lamp as bright as a 60-watt incandescent lamp dropped from U.S. $70 to $10. Meanwhile, the efficiency (or efficacy) of LEDs for turning power into light (as measured in lumens per watt) increased, as did their working lifetime, which greatly lowered their effective operating costs. See also: Fluorescent lamp; Illuminance; Illumination; Incandescent lamp; Lamp; Light-emitting diode; Luminous efficacy; Luminous efficiency; Luminous flux

Many trees enjoy extremely long lives in comparison to humans and other animals. Yet one group of trees, the bristlecone pines, stands out as the most ancient of all, with individual trees that commonly live for thousands of years, including one that has survived more than 5000 years. See also: Tree

Caenorhabditis elegans is a small, unsegmented, transparent member of the order Rhabditida in the phylum Nematoda (Nemata). Measuring approximately 1 millimeter in length in its adult form, this roundworm is typically found in soil, often feeding on bacteria among rotting vegetation and decaying organic matter, and is nonparasitic (free living) and nonpathogenic. Despite being a primitive invertebrate, C. elegans possesses many of the anatomical features and organs found in higher-level animals, such as those pertaining to its nervous, reproductive, muscular, and digestive systems; however, it lacks a circulatory system and a respiratory system. Because C. elegans is transparent, easily observed and manipulated, has a relatively short life cycle (2–3 weeks), and can be cultivated in large numbers under laboratory conditions (with 10,000 nematodes per petri dish), researchers frequently use it to study questions that would be difficult to explore directly in humans and other animals. In particular, because the cells of C. elegans hold steady in number and position in the body throughout its life, it is a popular model organism in developmental biology, embryology, genetics, and neuroscience. See also: Developmental biology; Developmental genetics; Embryology; Genetics; Invertebrate embryology; Nemata (Nematoda); Nervous system (invertebrate); Rhabditida

Cafestol, C₂₀H₂₈O₃, is a compound, specifically a diterpene alcohol, found in coffee beans. It is extracted during the coffee-brewing process and may be present in coffee beverages, depending on the preparation method. Consumption of cafestol in coffee has been shown to produce both positive and negative health effects. See also: Coffee; Terpene

In an application of green chemistry, researchers reported in the journal Biomaterials (April 2018) the caffeine-catalyzed synthesis of a new class of polymer gels for drug delivery and other biomedical applications. These caffeine-catalyzed gels (CCGs) are easy to make and are customizable in terms of their chemical and physical properties, such as their composition, shape, solvent sensitivity, drug release, and mechanical strength. The gels have potential to be consumed as chewable and easier to swallow drug-delivery systems. They contain a small amount of caffeine but were found to be safe in toxicity tests. See also: Biomedical engineering; Caffeine; Catalysis and catalysts; Citric acid; Drug delivery systems; Gel; Green chemistry; Polymer

The nearest images of the Sun obtained to date have revealed a new phenomenon, dubbed campfires, which appear as small, bright flickers of light all over the Sun's surface. The Solar Orbiter, a European Space Agency spacecraft launched in February 2020, captured the images from a distance of 77 million km (48 million mi), or about half the distance between Earth and the Sun. The Solar Orbiter will gather vastly more and better observations of campfires as the probe's mission continues for at least the next seven years, with a flight path that will ultimately take the probe to a distance of less than 0.3 astronomical units from the Sun, reaching inside the orbit of Mercury. [An astronomical unit is the average Sun–Earth distance of about 150 million km (93 million mi)]. See also: Astronomical unit

The cancer death rate in the United States has fallen by 27% since 1991. According to the American Cancer Society, which compiled the data over a 25-year period from 1991 to 2016, a total of 2.6 million fewer individuals have died from cancer in the United States. This remarkable decrease, which is a trend observed in both males and females, is attributed to a number of factors. The most notable factors are (1) the continual awareness and dissemination of information about the link between lung cancer and tobacco smoking, resulting in large reductions in the number of individuals who smoke; (2) advancements in early screening and detection methodologies; and (3) more effective cancer treatments and chemotherapies. In addition, there has been overall increased awareness on the part of individuals to avoid exposure to a multitude of other cancer risk factors. For example, individuals are more prone than those in the past to avoid certain carcinogens in their diet and to limit their exposure to the Sun's ultraviolet (UV) rays in order to maintain a healthier lifestyle. See also: Cancer; Chemotherapy and other antineoplastic drug treatments; Death; Nutrition; Oncology; Tobacco; Ultraviolet radiation (biology)

One of history’s worst agricultural catastrophes was the great Irish potato famine of 1845–1849, which killed more than a million people in Ireland, forced the emigration of 1.5 million others, and fueled resentments between the Catholic and Protestant factions of the country for generations. The precise pathogen responsible for that catastrophic failure of the Irish potato crop was long a matter of speculation among agricultural researchers. In 2013, however, using DNA-based analytical techniques on samples of old potato leaves preserved in herbariums, an international team of scientists pinned the blight to a single strain of a common fungus. Beyond the value of this discovery in illuminating what triggered the potato famine, it marked the first time that researchers were able to study the genome of an extinct botanical pathogen from traces in old cuttings of its host plant. See also: Deoxyribonucleic acid (DNA); Disease ecology

Sinkholes form when surface sediments collapse, sometimes dramatically, into a cavity below. They can be an unintended consequence of human activity. For example, on May 22, 2014, after a water main burst on the Lower East Side of New York City, the torrent beneath the pavement caused a sinkhole to devour a 20- × 15-ft (4.5- × 6-m) chunk of East Houston Street outside of Katz’s Delicatessen, a local landmark.

Neonicotinoid insecticides are the most used insecticide worldwide and have been linked to the decline of pollinator insects. In 2018, the European Union banned the outdoor use of three neonicotinoid insecticides: clothianidin, imidacloprid, and thiamethoxam. A new sulfoximine-based insecticide, called sulfoxaflor, is coming to market worldwide as a neonicotinoid replacement. Sulfoxaflor acts on the central nervous system of insects, just as neonicotinoids do, and, surprisingly (or not), it has similar harmful effects on wild bumble bees, researchers reported in Nature (August 2018). See also: Die-off of bees; Hymenoptera; Insecta; Insecticide; Neonicotinoid insecticides banned in Europe; Pesticide; Pollination

Handheld electronic devices with plastic casings, such as cell phones, may be exposing users to toxic organophosphate ester (OPE) flame retardants that leach out of these products. Researchers from the University of Toronto reported in Environment International (December 2018) that people in contact with cell phones showed evidence of hand-to-mouth and skin-absorbed OPE exposure. To test the relationship of these exposure pathways, the researchers measured OPE concentrations from air, dust, hand, electronic product, and urine samples. They detected OPEs as well as OPE urinary metabolites in more than 80 percent of the samples. In addition, they found greater evidence of OPE exposure from cell phones than from tablets, desktop computers, and televisions. See also: Fire technology; Flameproofing; Organophosphorus compound; Phosphorus; Polymer

People consider visual perception to be one of the most trustworthy means of gathering information about the world. However, striking limitations in visual processing occur daily, distorting the precision and completeness of the visual experience and demonstrating that substantial changes in a visual scene often go undetected. In particular, the role of attention in perceptual analysis is paramount for full and accurate comprehension of a visual scene. If certain aspects of visual attention are absent, or at minimum not applied specifically, then change blindness—the inability to discern large changes that occur in clear view of an observer—can occur. Remarkably, the phenomenon of change blindness can be elicited under circumstances in which the changes are made repeatedly and the observer knows that they will occur. See also: Cognition; Neurobiology; Perception; Psychology; Vision; Visual attention

Charles Robert Darwin (February 12, 1809 – April 19, 1882) is one of the most celebrated and eminent scientists of the past few centuries, with his broadest and most notable influence arising from his theory of evolution by means of natural selection. Darwin’s remarkable investigations and insights obtained during his voyage on the HMS Beagle (1831–1836) led him to theorize about concepts of evolutionary biology and to develop revolutionary ideas related to adaptation and speciation. Although previous scientific thinkers had laid down some of the foundations for Darwin’s work, and others later expanded upon and more fully developed the scientific bases for his conclusions, Darwin set forth and formulated the controversial but coherent ideas about organic evolution that have impacted the world at large. His groundbreaking On the Origin of Species was originally published in 1859. Later, in 1871, Darwin argued in The Descent of Man and Selection in Relation to Sex that humans had evolved just as other organisms had, creating a storm of controversy that continues today. See also: Adaptation (biology); Animal evolution; Organic evolution; Plant evolution; Speciation

An experiment at the Large Hadron Collider (LHC), the world's largest particle accelerator, has revealed the first evidence for a phenomenon known as charge-parity (CP) violation in the decays of subatomic particles called charm quarks. The results could help researchers get closer to explaining why matter dominates over antimatter in the universe, enabling galaxies, stars, planets, and—ultimately—living organisms to exist. A key theory in physics, CP symmetry holds that physical laws should stay the same if a particle's electric charge is switched—that is, if a particle is swapped for its antimatter counterpart—and if the particle's spatial coordinates are inverted, presenting a mirror image of itself. See also: CP symmetry and its violation; Electric charge; Parity (quantum mechanics); Symmetry breaking; Symmetry laws (physics)

Plastic is a ubiquitous and life-saving product, but it is also rapidly becoming a significant environmental problem. Globally, less than 10 percent of plastics are recycled, about 12 percent are incinerated, and the vast majority are disposed of in landfills or littered in the natural environment. Reasons for this low rate of recycling include the low cost of feedstocks (monomers) derived from oil; inexpensive landfill space; and the fact that some plastics, such as poly(vinyl chloride), low-density polyethylene, polypropylene, and polystyrene have chemical properties that make them difficult to recycle. See also: Petroleum products; Plastic waste pollution; Polymer; Polyolefin; Polystyrene; Polyvinyl resins

According to new research, young adults who reported higher stress during their childhood and teenage years to adulthood are more likely to suffer high blood pressure, obesity, or other cardiometabolic risk factors than their less-stressed peers. Known cardiometabolic risk factors include age, sex, family history, hypertension, smoking, dysglycemia (abnormality in blood sugar stability), and dyslipidemia (the imbalance of lipids such as cholesterol, triglycerides, LDLs, and HDLs in the body). Now, a group of researchers has found a new risk factor: childhood stress. See also: Cholesterol; Lipoprotein; Triglyceride (triacylglycerol)

For over 30 years, predictions that lithography for microelectronics and nanoelectronics would reach its limit have been overcome by engineers pulling out of their hats every imaginable optical trick for shrinking linewidths to cram more and smaller transistors onto the horizontal plane of a single chip. Now, in the quest to build smaller, faster, less-expensive devices, chip architects are following the lead of city planners who ran out of real estate for expanding horizontally: They are looking up. With vertical integration techniques, chipmakers can arrange transistors in three dimensions, not just two. See also: Integrated circuits; Microlithography

Mosquito repellents are natural and synthetic chemical compounds that are applied to skin, clothing, and sometimes home furnishings such as bed nets. For years, they have been an important defense against mosquito-borne diseases, such as Dengue fever, malaria, and West Nile virus, and most recently Zika virus. See also: Diptera; Insect diseases; Insecticide; Malaria; Mosquito: vector of disease; West Nile virus; Zika virus disease

It has been a long-held belief that, as a result of hunting habits, early humans were partly or even primarily responsible for the decline and eventual extinction of most of the largest mammalian species that inhabited ancient Africa. These large plant-eating mammals, called megaherbivores and weighing more than 1000 kg (2200 lb) each, displayed an incredible biodiversity and numbered more than 30 species in the past, but only a handful remain today: the hippopotamus, the black rhinoceros and white rhinoceros, four species of giraffe, and two species of African elephants (the larger African bush elephant and the smaller African forest elephant). However, more detailed analyses of the parameters and factors involved in the demise of ancient African megaherbivores suggest that humans did not cause the extinction of these mammals. Instead, changes in the ancient climate of Africa, in addition to the concomitant changes in African ecosystems and food sources, led to the extinction of the majority of these creatures. See also: Africa; African mammals; Animal evolution; Biodiversity; Elephant; Extinction; Giraffe; Global climate change; Hippopotamus; Proboscidea; Rhinoceros

Researchers from Rice University in Houston, Texas, United States, have found that climate change could potentially increase the size of stalled high-pressure weather systems (ridges) known as “blocking events,” according to global climate modelling simulations. Past studies had looked at how climate change might affect the number of blocking events, but these studies had not looked at the extent to which blocking events might change. In the northern hemisphere, such blocking events could increase the area affected by as much as 17 percent, resulting in larger extreme weather events that would affect more people and wildlife habitats. See also: Air pressure; Climate modeling; Extreme weather events; Global climate change; Meteorology

Wind-pollinated plants—including trees, grasses, and weeds—produce most of the pollen that affects seasonal allergy sufferers. Wind-pollinated plants produce great amounts of pollen grains that are very small in size. For example, one ragweed plant can produce 1 billion dustlike pollen grains. These small pollen grains are capable of travelling long distances by the wind, potentially affecting large numbers of people who suffer from pollen allergies. Allergy symptoms can range from nuisance manifestations, such as itchy eyes and runny nose for those with allergic rhinitis (also known as hay fever) to severe health hazards for those with allergic asthma. Unfortunately for those who suffer such allergies, researchers in North America and Japan have reported earlier start dates for pollen seasons as well as increased concentrations of airborne pollen. These increases have occurred since (in North America) and before (in Japan) 1990, and the researchers attribute these changes to global climate change. See also: Allergy; Asthma; Global climate change; Pollen

Astronomers have discovered the closest black hole on record, located 1,100 light-years away from our solar system. This black hole is part of the star system HR 6819, which consists of two bright, bluish stars. On a clear, dark night, these stars can be seen with the naked eye in the constellation Telescopium from the Southern Hemisphere. See also: Black hole; Constellation; Light pollution; Light-year; Star

High within the coldest and driest continent, Antarctica, lies what may be an environment too hostile to support life, according to a team of scientists from Canada and the United States. They reported finding no evidence of microbial life in the dry permafrost and underlying ice-cemented soil of University Valley, located 1700 meters above sea level in the McMurdo Dry Valleys of Antarctica, which is mostly snow-free and never gets above freezing (Journal of the International Society for Microbial Ecology, January 2016). The single drier place on Earth is generally considered to be the Atacama Desert in Chile. See also: Antarctica; Desert; Hyperaridity and the dry limits of life; Permafrost

For the first time, scientists have observed two molecules meeting and reacting to form new molecules. A team of chemists used lasers to slow down interacting molecules to temperatures far colder than outer space, enabling the team to observe a chemical reaction colder than any on record or that could ever transpire in nature. The finding offers important insights into how chemical reactions transpire on a fundamental level, opening the door to a deeper understanding and potential control of reactions, which could subsequently be used to develop new materials and processes. See also: Chemistry; Laser; Molecule

Among the most compelling exoplanets discovered to date is a "super-Earth" around Barnard's star, the closest single star to our solar system. This star, a cool red dwarf significantly smaller than the Sun, is located only six light-years away—just a bit farther than the nearest stars, the triple-star Alpha Centauri system. The proximity of its parent star makes the newfound world a potentially excellent candidate for detailed studies with future instruments. See also: Alpha Centauri; Earth; Exoplanet; Light-year; Planet; Solar system; Star; Sun

Colony collapse disorder (CCD) is a baffling detrimental condition in colonies of honeybees (Apis mellifera). It is characterized by a rapid loss of the adult bee population, with an absence of dead bees in and around affected colonies. No single cause of CCD has been identified, but numerous stressors, including compromised immune function, viral pathogens, and exposure to pesticides and insecticides (in particular, neonicotinoids), have been proposed as probable causes. Since the initial description of CCD in 2006, this disorder has resulted in significant reductions in the numbers of adult honeybees, which are the predominant pollinators of numerous economically important plants and crops. The decreases in honeybee populations explicitly due to CCD continued until at least 2015. However, entomologists are now noticing that the threat assigned to CCD seems to be decreasing dramatically. Some researchers even believe that CCD, as a specific phenomenon or disorder, has vanished (although it may be in a dormant state). Overall, bee colonies are still suffering losses, but researchers are less concerned about CCD and have shifted their attention to the general health of bees, trying to determine how nutrition, pesticides, pathogens, and parasites are affecting bee populations. See also: Colony collapse disorder; Economic entomology; Hymenoptera; Insect diseases; Insecticide; Parasitology; Pathogen; Pesticide; Pollination; Population ecology

Colorectal cancer (also termed colon or bowel cancer) is the third most prevalent type of cancer both in men and in women, taking the lives of approximately 400,000 people annually worldwide (including 50,000 people per year in the United States). It results when tumors form in the lining of the large intestine's colon or rectum. Since the year 2000, the number of cases and mortality rates of patients having colorectal cancer have risen dramatically among young and middle-aged adults in the United States. Specifically, in adults younger than age 50, the incidence rate of colorectal cancer has increased by 22%, with an accompanying 13% increase in the death rate from this condition. These statistics are surprising because the rates among persons more than 50 years of age have been dropping, predominantly because of their adoption of healthier lifestyle habits (such as smoking less and eating less red meat) and improvements in medical screening and treatment protocols. Thus, the rise of colorectal cancer in the younger population is a troubling shift. See also: Cancer; Colon; Digestive system; Gastrointestinal tract disorders; Intestine; Oncology; Tumor

Obscured by a hazy atmosphere 100 times thicker than Earth's, Venus is a notoriously difficult world to study. Ground temperatures on Venus exceed 450°C (842°F)—enough to melt lead and to have quickly degraded the Soviet robotic landers last placed there 40 years ago. Yet orbiting spacecraft have successfully mapped this planet with cloud-piercing radar, as well as identified constituent surface materials via narrow bands of infrared light that escape the Venusian atmosphere. Those investigations have revealed unmistakable volcanic structures and solidified lava flows, although there remains no definitive evidence as to whether volcanic eruptions still occur. Now, a new study suggests that such evidence is already in hand and points to Venus as the only other volcanically active planet in the solar system. See also: Atmosphere; Radar; Venus; Volcano

After 13 years studying Saturn and its moons, the Cassini spacecraft’s mission ended on September 15, 2017. Operators at NASA intentionally directed Cassini to plunge into Saturn’s atmosphere, destroying the spacecraft before its fuel supply ran out and the ability to control the probe’s path was lost. Mission planners made this decision to protect against Cassini possibly crashing into Saturn’s moons Titan and Enceladus, which were discovered during the mission to possess environments that could potentially support alien life. See also: Planet; Saturn; Solar system; Space probe

Dawn, a pioneering mission to our solar system's asteroid belt, has gone silent. In late October 2018, Dawn ran out of hydrazine, the thruster fuel needed to orient the spacecraft for communication with Earth and the generation of solar power. Although now retired, the Dawn mission leaves a rich scientific legacy. It is the first and only spacecraft to have visited the dwarf planet Ceres—the largest object in the asteroid belt between Mars and Jupiter—as well as Vesta, the second-largest object in the belt. Before Dawn's arrivals, humanity had little clue as to what these worlds really looked like. See also: Asteroid; Ceres; Earth; Dawn mission; Hydrazine; Jupiter; Mars; Planet; Solar cell; Solar system; Space communications; Vesta

NASA's Curiosity rover has produced new key evidence in determining whether Mars has ever hosted life. While drilling in an ancient lakebed, Curiosity recently discovered organic material more complex and abundant than previously found on the Red Planet. On Earth, chains of organic molecules, which contain the element carbon, form the basic building blocks of life. Far more investigation will be necessary, however, to identify the source of the Martian material as either biological or geological. Besides life, likelier sources of the organic material include impacting asteroids and volcanism. See also: Asteroid; Astrobiology; Carbon; Geology; Mars; Organic chemistry; Volcano

Neuroscientists have long sought to explain how the brain correctly recognizes a stimulus despite the stimulus appearing under different circumstances with widely variable external factors. For example, with regard to olfactory stimuli, humans can correctly identify the smell of coffee regardless of location, time of day, ambient conditions (such as temperature and humidity), or other potentially confounding contexts. Researchers term this ability "invariant odor recognition," and when generalized to other senses, "invariant stimulus recognition." A new study now offers insight into invariant odor recognition in locusts. Scientists at Washington University in St. Louis, Missouri, United States, found that a simple arithmetical expression of neuron activations reliably predicted when a locust recognized a particular odor. The findings could improve our general understanding of how olfaction operates in animals and improve the performance of artificial chemical sensing systems, which have a range of applications in environmental monitoring, security, medicine, and other fields. See also: Arithmetic; Chemical senses; Olfaction; Neuron

The critically endangered northern white rhinoceros (Ceratotherium simum cottoni) is a subspecies of white rhino that is on the brink of complete extinction, with only two individuals left in captivity and no known members reported in the wild. The two remaining individuals are a mother (named Najin) and her daughter (named Fatu) residing at the Ol Pejeta Conservancy in Kenya. As both females are unable to reproduce naturally, scientists have taken the extraordinary step of producing viable embryos in the laboratory. In order to generate the embryos, biologists extracted eggs from the female rhinos; then, the eggs were artificially inseminated with cryopreserved (frozen) sperm from two male northern white rhinos that had died in 2014 and 2006, but whose sperm had been kept in storage and subsequently thawed. Out of 10 eggs that were harvested, 7 successfully matured to the point that they were able to undergo fertilization. However, only 2 of these fertilized eggs (both derived from the daughter Fatu) developed into viable embryos. Until a satisfactory surrogate female individual (most likely a member of the southern white rhino subspecies, which has an estimated population of 20,000) is found, and into whose body either or both of the embryos can be transferred, the 2 embryos have been frozen in order to preserve them for future use. See also: Africa; Cryobiology; Endangered species; Extinction; Fertilization (animal); Genetics; Northern white rhinoceros on the brink of extinction; Population ecology; Population viability; Rhinoceros

Conifers are predominantly cone-bearing, evergreen trees and shrubs belonging to the order Pinales, as well as a small number of extinct orders, in the class Pinopsida of the division Pinophyta (Coniferophyta). All are woody plants, and they are often the predominant trees of forests worldwide, including pine, spruce, fir, hemlock, cedar, larch, juniper, cypress, yew, and redwood species. Because the ovules (young seeds) of these plants are exposed directly to the air at the time of pollination—that is, these plants produce seeds that are not enclosed in a fruit or ovary—conifers are classified as gymnosperms. (In contrast, the flowering plants, or angiosperms, have ovules enclosed in an ovary.) Today, conifers constitute the principal source of lumber and pulp for paper and wood products. See also: Forest and forestry; Forest timber resources; Lumber; Pinales; Pinophyta; Pinopsida; Tree; Wood products

Scientists have suggested a possible connection between ancient Neandertals (Homo neanderthalensis) and the severity of disease in patients affected by COVID-19. In short, certain genes acquired from Neandertals during instances of interbreeding with ancestors of modern humans (Homo sapiens) approximately 60,000 years ago may be involved in the susceptibility of individuals to severe disease from the virus that causes COVID-19. Specifically, researchers have identified a region on human chromosome 3 that possibly influences whether a person infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) will become seriously ill and require artificial ventilation. This chromosomal region is almost identical to a segment found in the DNA of Neandertals from Croatia and Siberia, and present-day carriers of the Neandertal-derived gene variant on human chromosome 3 have an increased likelihood of developing life-threatening forms of COVID-19. See also: Chromosome; Coronavirus; Deoxyribonucleic acid (DNA); Gene; Neandertal DNA; Neandertals; Novel coronavirus is declared a global pandemic

The novel coronavirus SARS-CoV-2 that emerged in central China in late 2019 and subsequently spread across the world in 2020 led to the COVID-19 pandemic. The emergence of a previously unknown pathogen—such as the novel coronavirus—that could affect much of the world's population has long been anticipated by many epidemiologists, who have been especially concerned about potential consequences of human-influenced (anthropogenic) global climate change as it relates to human health and disease. In fact, as a result of ecological changes attributed to anthropogenic global warming, including altered landscapes and ecosystems, modified predator-prey relationships, habitat destruction, deforestation, and rising land and ocean temperatures, numerous infectious diseases have spread into new geographic regions in recent years, leading to more infections in animal populations. These newly infected animals are interacting with humans to a greater degree than ever before, creating more opportunities for zoonotic disease transmission (that is, transmission from animals to humans). See also: Deforestation; Ecosystem; Epidemiology; Global climate change; Global warming; Infectious disease; Novel coronavirus is declared a global pandemic; Predator-prey interactions; Virus; Zoogeography; Zoonoses

The world’s oceans and coasts provide a natural sink for excess carbon in the atmosphere. Scientists refer to carbon that is captured and stored this way as blue carbon. Well-known blue-carbon examples include mangroves and salt marshes—wetland ecosystems in which the soils may store carbon for thousands of years. An often-overlooked source of blue carbon, however, is large fish living in the open ocean, according to marine scientists reporting in the journal Science Advances (October 2020). Large fish are classified as being longer than 30 centimeters (12 inches) in length, and include such species as tunas, mackerels, sharks, and billfishes. See also: Carbon; Chondrichthyes; Mackerel; Mangrove; Salt marsh; Soil; Perciformes; Pisces (zoology); Tuna; Wetland

Monarch butterflies (Danaus plexippus) exclusively consume milkweed plants (genus Asclepia) both for nutrition and to help deter predators. Milkweed plants contain toxins that accumulate in the butterfly larva, or caterpillars, as the insects feed; those toxins then persist into the adult stage. Monarchs have evolved specific genetic mutations that protect their species from these poisons. Yet various organisms, including black-headed grosbeaks (a kind of bird) and eastern deer mice, as well as parasitic wasp and nematode (worm) species, can withstand the toxin and readily eat monarch butterflies. A new study has now shown how this is possible: all four predators, it turns out, have evolved monarch-like genetic mutations in their respective genomes that confer milkweed toxin resistance. The findings are a remarkable example of convergent evolution across distantly related organisms, whereby organisms independently evolve similar traits as they adapt to comparable environments and selection pressures. See also: Adaptation (biology); Convergent evolution; Evolution; Genetics; Gentianales; Insecta; Lepidoptera; Mutation; Plant-animal interactions; Poisonous plants; Toxin

Over the next 10 to 20 years, capturing carbon dioxide (CO₂)—a powerful greenhouse gas emitted from sources such as fossil-fuel-burning power plants, natural-gas processing plants, bioethanol plants, and cement plants—could become a significant method for mitigating climate change. Most of the captured CO₂ would probably be injected deep into the earth, a practice known as carbon capture and storage (CCS). The U.S. Department of Energy (DOE) estimates that the current cost to capture a ton of CO₂ is $60, which is cost prohibitive. With technological improvements, the DOE projects the cost to capture a ton of CO₂ could drop to a more affordable $40 in 10 years. See also: Carbon capture and storage; Carbon dioxide; Cement; Electric power generation; Global climate change; Greenhouse effect; Natural gas

If you think converting seawater to fuels that can power ships is a fantasy, think again. Researchers at the U.S. Naval Research Laboratory in Washington, D.C., have, in fact, accomplished this feat. In addition, the U.S. Navy has received a patent for an electrochemical device that removes carbon dioxide (CO₂) and hydrogen (H₂) gases from seawater, which together can be converted through a catalytic reaction to liquid hydrocarbon fuels that are similar to fossil fuels. Breakthrough technology aside, don’t expect to see U.S. Naval ships powered by fuels from seawater cruising the high seas anytime soon. Making significant quantities of this fuel requires processing a great deal of seawater, which, in turn, requires a large amount of electricity to drive the electrochemical process. Nevertheless, researchers expect efficiency improvements over the next 10 years to bring the concept closer to reality. See also: Carbon dioxide; Catalysis and catalysts; Electrochemical process; Fossil fuel; Hydrogen; Seawater

In the journal Science (September 2018), researchers reported a method for making a coating that reflects sunlight and radiates heat. The coating can be used to cool buildings and reduce air-conditioning use, keeping surfaces painted with the material about 6 degrees Celsius cooler than the surrounding air temperature. The paint can be easily applied to most surfaces, including the exterior walls and roofs of existing buildings. The cooling effect is based on a phenomenon known as passive daytime radiative cooling, whereby a surface cools without any energy input by reflecting ultraviolet to near-infrared solar radiation (278- to 4600-nanometer wavelengths) and radiating long-wave radiation (8000- to 13,000-nanometer wavelengths) through the atmosphere to outer space. Cool roofs designed using metals (such as aluminum) or white-pigmented paints help keep building temperatures lower by reflecting sunlight but are less effective at emitting the heat they absorb because heat is reflected inside these materials. See also: Buildings; Emissivity; Heat transfer; Infrared radiation; Paint and coatings; Radiation; Reflection of electromagnetic radiation; Solar radiation

As the global climate becomes hotter and drier, heat mitigation in urban areas through the use of cool roofs is becoming increasingly important. Cool roofs reflect more sunlight and absorb less heat than conventional roofs, according to the U.S. Department of Energy. In addition, cool roofs reduce air-conditioning requirements, greenhouse-gas emissions, and impacts to human health, including death during heat waves. Researchers from the Lawrence Berkeley National Laboratory (Berkeley Lab), Berkeley, California, reported an added benefit of cool roofs in Nature Communications (October 2017); that is, they found through regional climate simulations that cool roofs not only reduce indoor and outdoor temperatures, they also reduce outdoor irrigation water use by as much as nine percent. Los Angeles County, California, could save more than 80 million gallons of water per day, as a result, they said. See also: Albedo; Climate modeling; Drought; Global warming; Global climate change; Hydrology; Irrigation (agriculture); Plant-water relations; Urban climatology; Water conservation; Water resources

Astronomers have detected light from the “cosmic dawn,” the primordial epoch when the universe’s first stars began to shine. The long-sought discovery could throw open a window onto a previously inaccessible era, revealing the rise of stars and galaxies. The findings also offer new clues about dark matter, a mysterious substance that makes up 80 percent of matter in the universe. See also: Dark matter; Galaxy; Galaxy formation and evolution; Matter (physics); Star; Universe

Trees provide substantial benefits to the environment. In addition to improving air quality, reducing stormwater runoff, serving as a wildlife habitat, and sequestering carbon by absorbing carbon dioxide, trees also cool the atmosphere through shade and transpiration (loss of water vapor). As the world’s climate warms, some cities are planting trees to increase the amount of canopy cover needed to counteract the heat island effect, an atmospheric condition in which urban areas are warmer than their rural surroundings. The percentage of tree canopy coverage that is needed to realize a cooling effect had been largely unknown until researchers reporting in the journal Proceedings of the National Academy of Sciences of the United States of America (April 2019) measured the effect of canopy cover on daytime air temperature in a city in the Midwestern United States using bicycle-mounted sensors. See also: Global climate change; Plant-water relations; Tree; Urban climatology; Urban tree leaves remove fine-particulate air pollution

A newly identified coronavirus, provisionally termed 2019-nCoV (an acronym for 2019 novel coronavirus) and subsequently named "severe acute respiratory syndrome coronavirus 2" (SARS-CoV-2), emerged in central China in November 2019. The disease caused by this virus, called COVID-19 (an acronym for "coronavirus disease 2019"), is currently a pandemic (worldwide epidemic) that has sickened and killed millions of people around the world. The infectious virus initially affected individuals in the city of Wuhan, predominantly those working at or frequenting certain animal markets. At first, the virus was thought to spread from animals (possibly bats or pangolins) to people. However, affected individuals who did not have exposure to any animal markets were subsequently identified, indicating that person-to-person transmission was occurring. In addition, studies indicated that the virus remains stable for several hours to days in aerosols and on surfaces; thus, individuals can acquire the virus either via the air or after touching contaminated objects. The many initial unknowns regarding this novel coronavirus and the rapidity with which it is spread prompted the World Health Organization (WHO) to declare COVID-19 a global health emergency on January 30, 2020. On March 11, 2020, the WHO officially announced that COVID-19 was a pandemic. See also: Animal virus; Coronavirus; Disease ecology; Epidemic; Epidemiology; Infectious disease; Virus; Virus classification

A compound found in cranberries, called cranberry proanthocyanidin (cPAC), when used in combination with antibiotics, such as tetracycline, prevents resistance to antibiotics in Escherichia coli and Pseudomonas aeruginosa, according to researchers reporting in the journal Advanced Science (May 2019). In addition, the combined use of antibiotics with cPAC inhibits biofilm formation, another a route toward antibiotic resistance. This type of synergy—whereby one substance that does not normally produce a desired effect makes a second substance significantly more effective—is called potentiation. See also: Antibiotic; Antibiotic resistance; Biofilm; Cranberry

Crown-of-thorns starfish or sea stars (Acanthaster planci; order Valvatida) are predatory marine invertebrates that feed on phytoplankton found on coral. They are native inhabitants of coral reefs in both the Indian Ocean and Pacific Ocean and are particularly common on the Great Barrier Reef, which is the largest living structure in the world, covering an area of more than 340,000 km² (131,000 mi²) off the northeast coast of Australia. Lately, crown-of-thorns sea stars are exploding in numbers, offsetting the ecosystem balance found in the waters of the Great Barrier Reef and causing marine investigators to fear severe degradation of the coral reefs, which are already under pressure from coral bleaching (the response of corals to environmental stress in which they eject the algae that live within the transparent coral tissue, making the white coral skeleton visible) and other effects of rising sea temperatures. See also: Asteroidea; Australia; Coral bleaching; Coral reef complexity; Ecological communities; Ecosystem; Marine ecology; Ocean warming; Reef; Severe coral bleaching endangers Great Barrier Reef; Valvatida