Since the Scopes Trial in 1925, several transitional fossils have been discovered that document the progression to modern humanity and will aid in solving the problem of the “missing link.” Now the work of 40 scientists across eight different countries aims to shed light, not on how the hominid changed, but why.

Andrew Cohen, a professor of geosciences at the UA, and his research group received $4.78 million to continue research on the climate of hominin fossil locations over time and its effect on the movements and evolution of the area’s animal inhabitants, with a focus on humans.

Cohen is the director of the Hominin Sites and Paleolakes Drilling Project, which focuses on drilling into lake beds in Kenyan and Ethiopian rift valleys — valleys created by the movement of tectonic plates at a rift or fault.

“The goal of this project,” Cohen said, “is to understand the atmospheric conditions in the region and hopefully connect that to events in human evolution.”

By gathering climatological data near where hominin fossil discoveries were made, the researchers are hoping to build computer models that can simulate the atmospheric behavior of Earth.

In the designated sites — lake beds that are either dry or shallow — cylinders are drilled into the Earth and then removed, bringing with them a column of mineral history for that region. These samples are called drill cores.

The scientists must then figure out when those materials were deposited in that spot.

“We use various kinds of absolute dating techniques that geologists have developed,” Cohen said.

For active lakes, the age of the upper minerals can be easily determined by carbon dating, a method that determines age by analyzing the decay of carbon isotopes.

Unfortunately, carbon dating can only be used for materials that are under 50,000 years old. The group is more often interested in samples that are between 2.5 and 3 million years old.

“The most important [technique] for the older deposits is based on the decay of radioactive potassium in argon gas,” Cohen said.

Potassium argon dating can be used to date material whose age ranges from around 100,000 years to about 4.55 billion years, the age of the Earth.

By collecting these sediment drill cores, the team hopes to gather data regarding the ancient chemical, sediment and ecological history of the region.

This will help to reconstruct data on precipitation, temperature, hydrology and geomorphic evolution, within which the researchers hope to identify geological and chronological thresholds of environmental change.

The purpose of the project is to form new, testable hypotheses on human evolution and the dynamics of Earth’s systems, which will help create digital models that can be used to predict patterns in hominin and other animal populations, and to hindcast weather patterns relevant to evolutionary geology.

Finding the relationship between hominin behavior and climate conditions may help lay the source of one of our greatest curiosities to rest.