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Terrestrial Origins and Evolution
black algal mat Pleistocene


Skeletal remains of mammoth, horse, camel, Dire wolf, and others tell of the megafauna that roamed southern Arizona during the Pleistocene Epoch until these large animals became extinct 13,000 years ago. The time of extinction coincides with the deposition of a black algal mat, visible as a black line just above the mammoth tooth in this photo, of Younger Dryas age, when hunter-gatherers of the Clovis culture inhabited the area. No remains of Pleistocene mammals have ever been found in sediments deposited above, and thus younger than, the black layer. UA scientists unearthed the fossil pictured here southeast of the Murray Springs Clovis site, where they sampled the black algal layer to test the hypothesis of cosmic impact as the cause of extinction and Younger Dryas cooling. Credit: Photo courtesy of the Center for the Study of the First Americans

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