Investigators reported in Geology last week that the environmental variability suggested by the geochemical record of Lake Magadi is associated in time with mammal species turnover and the first appearance of Middle Stone Age technology in the southern Kenya Rift between 500,000 and 320,000 years ago.
The investigators drilled Lake Magadi as part of the Hominin Sites and Paleolakes and collected deep sediment cores from lake basins in the East African Rift.
They will examine the geochemical record of drill core sediments collected from Lake Magadi—an internally drained, saline and alkaline terminal sump in the southe Kenya Rift—that provides a nearly one-million-year paleoenvironmental record from an unusual Rift Valley Lake system.
“We are trying to understand how the Earth’s surface environment has changed over the last several million years and how that has impacted early hominin habitats,” said drilling project lead investigator, Dan Deocampo of Georgia State University.
“We are using many different proxies of the ancient environments to understand how the environment has changed, how habitats have changed .”
The researchers also said in their report that geochemical analysis of the Lake Magadi samples showed some of the highest concentrations of elements like molybdenum, arsenic, and vanadium ever reported in lake sediments.
Geochemistry of samples representing the past close to one million years of the lake’s history show some of the highest concentrations of transition metals and metalloids ever reported from lake sediment, including redox-sensitive elements including arsenic, vanadium and molybdenum —a silvery transition metal renowned for its exceptional corrosion resistance and very high melting point.
Most molybdenum is used to make alloys and in steel alloys to increase strength, hardness, electrical conductivity and resistance to corrosion and wear. Elevated concentrations of these elements represent times when the lake’s hypolimnion was euxinic — that is, anoxic, saline, and sulfide-rich.
Euxinic conditions occur when the lake water is both anoxic and sulfidic, typically triggered during negative water balance episodes like droughts.
“The molybdenum accumulated in a sulfide-rich sediment in the lake is not going to tell us habitat structure, where the hominins lived, but fluctuations between those euxinic conditions and fresher water conditions, can tell us something about the pace of environmental change,” said Deocampo