One of our best views of the Neogene comes from a sinkhole near Gray Tennessee, where scientists today continue to excavate the fossil bones of animals long gone from the region -- hippo, rhino, elephant, panda, camel, giant sloth, saber-tooth tiger and alligator.

East Tennessee State University has sponsored a Natural History Museum, preparation laboratories and exhibits that recreate a landscape that a mere five million years ago was much warmer and stranger than the Tennessee we know today.

But at the top of our Neogene timeline, a barely visible sliver of time would hold an even bigger surprise.

Antarctica had settled over the south pole, cooling the Earth with a circumpolar ocean current driven by the Earth's rotation. Billions of cubic miles of fresh water were gradually sequestered into a sun-reflecting snow pack, and in a final event, North and South America were linked by a land bridge, creating the Gulf Stream. These events would plunge us into a much colder period.

The Earth with its shrinking oceans had already undergone trial by fire. Wobbling like a spinning top, our oscillating planet would soon be subjected to a new challenge --trial by ice, and the Ice Ages would catalyze the appearance of the most disruptive of all animal orders . . . the primates.

Five Million year-old Short-Faced Cave Bear from Gray, Tennessee, photo by Cheryl Davison