PASADENA, Calif.East Africa's Turkana Basin has been a hot savanna region for at least the past 4 million yearsincluding the period of time during which early hominids evolved in this areasays a team of researchers led by scientists at the California Institute of Technology (Caltech). These findings may shed light on the evolutionary pressures that led humans to walk upright, lose most of our body hair, develop a more slender physique, and sweat more copiously than other animals.
Their findingswhich were based on measurements of the spatial distribution and concentrations of isotopes in carbonate ionsare being reported this week in the early online edition of the Proceedings of the National Academy of Sciences (PNAS).
"When you measure the temperature of the ground, you learn a lot about the environment above it," says John Eiler, Robert P. Sharp Professor of Geology and professor of geochemistry at Caltech. In fact, he says, soil temperature tells you not just about air temperature, but about whether there were trees and plants to shade the soil, keeping temperatures cooler during the hottest part of the day.
Today, northern Kenyawhere the Turkana Basin is foundis among the warmest areas on earth. It has little canopy forest, leaving the ground exposed to sunlight. "The question is, was the ground here ever cooler than it is today?" asks Eiler. "And if it was, why? Was it because the air was cooler, or because of more forest shading?"
To find out, the team examined the spatial organization (or "clumping") of rare, naturally occurring isotopes of carbon and oxygenspecifically, carbon-13 and oxygen-18in the form of carbonate ions that are constituents of minerals found in buried soils from northern Kenya. The clumping of these isotopes, Eiler and his colleagues have demonstrated in previous papers, is dependent on temperature: Hot temperatures lead to less clumping; cold temperatures, more.
"These carbonates ar
|Contact: Lori Oliwenstein|
California Institute of Technology