^^

One of the most informative clues to the ancient ecology of Olduvai is the wealth of fauna preserved in its piled layers of time. A little over a million and a half years ago, “profile of the swampy habitats, such as hippo, abruptly disappeared, to be replaced by a greater frequency of species adapted to the drier conditions of a savannah habitat. This “faunal break,” echoed in the kinds of pollen preserved and the record of windblown and water-worked particles forming the deposits, coincided with the beginning of wide-spread faulting in the region.

Perhaps aided by global changes in climate, the giant shifts in the earth shrank the lake to a third of its size and set in motion a gradual eastward march of its damage sump, until it reached its present location in the Olbalbal Basin some 400,000 years ago. The changing portrait of water accumulation and drainage was of course of more than academic interest: Almost all animals, hominids included, need sources of fresh water. Locate the prevailing water-courses, and that’s where you’ll find bones and archaeological sites. In his work with Mary Leakey, Dick Hay found that by Bed III and Bed IV times, the traces of prehistoric humanity had spread out and dispersed along stream beds.

Today, Olduvai Gorge cuts a twenty-five-mile-long Y into the Serengeti. Where the narrower southern arm of the Y -- the Side Gorge -- meets the Main Gorge, there is a broad, flat area called the Junction. . . . Page 144