Tentative fossilized evidence of oldest animal life
An investigation of 890-million-year-old limestone rocks excavated from the mountains of Canada's Northwest Territories has revealed possible evidence of the oldest animal life on Earth. Prior to this study, the oldest undisputed fossils of animal life have been those of ancient sponges, or poriferans (members of the phylum Porifera), that lived approximately 540 million years ago during the Cambrian period. However, scientists analyzing thin sections of the Northwest Territories rocks identified three-dimensional tubelike structures that are similar to the structural network of certain modern sponges, thereby provisionally pushing back the beginnings of the earliest sponges by about 350 million years. If the findings of this study are confirmed, they would indicate the presence of animal life on Earth prior to the Neoproterozoic Oxidation Event, which was a period occurring between 800 million and 540 million years ago that boosted atmospheric oxygen levels closer to modern-day levels. Thus, the putative ancient sponges were likely tolerant of comparatively low oxygen levels, suggesting that the origins of animal life on Earth may have been less dependent on oxygen. See also: Animal evolution; Evolution; Fossil; Limestone; Oxygen; Paleontology; Petrography; Petrology; Porifera; Precambrian