The Tectonics of a Fossil Repository
(A) The continents sit on tectonic plates that slide over Earth’s upper mantle. But the African tectonic plate is gridlocked, so Africa cooks in the rising heat from Earth’s core. On the continent’s east side, magma wells up, fracturing the African plate into the Nubian and Somalian subplates. The result is the East African Rift (red lines), which extends through Eritrea, Ethiopia, Kenya, Tanzania, Malawi, and Mozambique. The Red Sea and the Gulf of Aden are also rifts, caused by the movements (arrows) of the Arabian plate and Africa’stwo subplates. The boundaries of the three plates (white lines) meetwhere the rifts all intersect, in what geologists call a triple junction.
(B) At the triple junction, the Afar Rift, the north end of the East African Rift, began forming more than 25 million years ago and grows wider and deeper every year. Magma rises there, pushing Earth’s crust up and back to form plateaus with a valley subsiding between them. In the past, sediments from the plateaus buried the remains of animals (including hominids) that were attracted to the valley. The result is a treasure trove of fossils that now attracts scientists. But it’s a disappearing treasure trove, eroding away and destined for a watery end. Part of the rift is already 512 feet below sea level. Water will eventually flood the area, then spill down the entire East African Rift, cutting off the Somalian plate.
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