Two million years ago, Olduvai Gorge was a large alkaline lake, fed by streams flowing from the slopes of the nearby volcanoes and volcanic highlands.

Hippos with eyes on protruding stalks, giraffes with large horns, dwarf elephants, sabre toothed cats and many other animals drank and hunted by the lakeshore. Our early ancestors, too, hunted, scavenged and lived by the shore of the lake. They made  tools from stones they located near the lake and in the nearby hills.

Some of the animals which died by the lakeshore had their bones quickly covered by  ash from erupting volcanoes. Some of these bones were preserved as fossils.

Over the millennia, the lake gradually filled with river borne sediments, windblown sand and layers of ash from the volcanoes.  Then, a sudden earthquake drained the lake.

Later, the Olduvai River, running only during the wet seasons, eroded its way through the layers of sediments and ash, forming a gorge that exposed layers of sediments dating back millions of years.

Fortunately for archaeologists, the gorge cut along the shoreline where rich deposits of fossils lay, rather than through the middle of the lake.  The eroding water revealed a complex layer cake of sediments, ash layers, stone tools, animal fossils and the fossil bones of early hominids.

Museum / SFU / Sandbox Dig