A "black mat" of algal growth in Arizona marks a line of extinction at 12,900 years
ago; Clovis points and mammoth skeletons were found at the line but not above it.
Credit: Allen West, UCSB
01/14/09
ago; Clovis points and mammoth skeletons were found at the line but not above it.
Credit: Allen West, UCSB" style="text-decoration:none">Full Size
