The Earth “is overdue for an ice age,” according to Peter deMenocal.
On Wednesday night, deMenocal, the guest speaker for the College of Science’s fourth Frontier of Science lecture, presented his work titled, “African Climate Changes and Animal Evolution.”
DeMenocal, a geology professor at Columbia University, also told the crowd that, as a result of an increase of greenhouse gases, “we’re pushing the Earth to a place it hasn’t been.”
Concerning the impending greenhouse problem, deMenocal said Americans would be wise to “embrace some changes in behavior,” but didn’t offer specific solutions.
Instead, deMenocal concentrated his lecture on the past and, more specifically, on how the climate affected evolution.
His studies primarily involve Africa and the core samples taken from the ocean floor surrounding the continent. The samples are composed of sediment that includes the dust blown into the ocean from Africa’s landscape. Presently, approximately 500 million tons of dust are exported annually, deMenocal said.
The core samples led deMenocal to conclude that the African climate before 2.8 million years ago had cycled between extremely wet and dry conditions every 20,000 years.
Those cycles became very different, however, as the Earth progressed to its present age. About 1.7 million years ago, the wet-to-dry cycles increased to 40,000 year periods and then to 100,000-year periods around 1 million years ago.
Major evolutionary events seem to have occurred during these shifts, deMenocal said.
For example, the evolution of humans into their present state coincides with the changes in climate intervals.
At about 2.9 million years ago, human relatives had moderate sized brains and large chewing teeth. In their place, about 2.6 million years ago, a relative evolved with a larger brain and smaller teeth. Finally, Homo erectus evolved with a brain similar in size to humans’ brains today.
The African climate intervals control vegetation, rainfall and temperatures. The Sahara Desert, deMenocal said, was almost completely vegetated 9,000 years ago. Wetland animal fossils such as hippopotamuses and crocodiles were discovered in parts of the desert. Ancient pictographs portrayed landscapes filled with antelope and sweeping grasslands.
DeMenocal’s studies help scientists piece together the changes the Earth has undergone, and may help shed light on the changes to come.
The fifth and final Frontier of Science Lecture will take place Wednesday, March 10. Guest speaker Christopher Johnson is the director of the U’s Scientific Computing and Imaging Institute. His lecture is titled, “Computing the Future of Biomedicine.”