The Hominin Sites and Paleolakes Drilling Project, led by Andrew S. Cohen of the University of Arizona, has received $2.88 million in grants: $1 million from the International Continental Scientific Drilling Programme and $1.88 million from the National Science Foundation.
To understand the past climate in which our ancestors evolved, project leaders will take samples from dry lakebeds in Africa’s Rift Valley that are near important fossil and archaeological sites of ancient hominins. Hominins are the group of organisms that includes humans and our near-fossil relatives and ancestors.
The researchers will drill into the lakebeds and collect more than 2.4 kilometers (1.5 miles) of cores of lake deposits. To collect the cores, the team will use a drill rig, similar to but smaller than what is used for oil well drilling. The drill rig is modified to collect continuous sediment cores from the hole in 10-foot segments.
The team will use samples of the microscopic fossils found in the cores, such as pollen and algae, as well as geochemical clues from the sediments, to study the connections between human evolution and past climate. They will reconstruct temperature and precipitation over the past 4 million years of Africa’s environmental history in the same areas and places where the hominins are known to have lived.
“This project has the potential to completely transform our understanding of how environmental and climate change affected the evolution of our ancestors, and particularly our own species. Understanding how hominins evolved and went extinct as a consequence of climate change also has profound implications for our own species today,” said Cohen, a UA professor of geosciences and the principal investigator and director of the project.
The East African rift valley of Kenya and Ethiopia, where the project will take place, has harbored many lakes over a time period that encompasses the entire history of human evolution.
Climate records from past geologic time periods have previously been compiled from deposits where the fossils and stone tools of human ancestors are found. However, those records, mostly from ancient river deposits or soils, generally do not provide a detailed account of environmental history. Anthropologists need detailed records to test hypotheses about what factors drove the evolution and extinction of early hominins.
Lake sediments, by contrast, can provide highly detailed records extending back millions of years. Information stored in lake sediments can inform us about past climate and environmental conditions in and around the lakes. By drilling cores from dry lakebeds adjacent to some of the most important fossil hominin and artifact sites in the world, Cohen and his team will provide a greatly improved understanding of the environmental and climatic conditions in which humans evolved.
The project involves more than 40 scientists and engineers from nine countries. Drilling will occur in five areas of Kenya and Ethiopia that include some of the most important locations and time intervals in the record of human evolution.
The oldest site the team will drill, in the Northern Awash River Valley, covers the time when "Lucy" and other members of the species Australopithecus afarensis lived (4-2.9 million years ago). “At this site, we expect to collect a continuous record of the entire environmental history of Lucy’s species in the area where the vast majority of its fossils have been found, including from time of its first appearance until its extinction more than 1 million years later,” said Cohen.
The team also will collect sediments from a paleolake near where the oldest fossil members of our own genus Homo have been found, in the central Kenyan Rift valley (approximately 3.2-2.35 million years old). At that site, researchers on the team have previously found a record from outcrops of lakes expanding and contracting, following wet and dry cycles in the region’s climate. However, the details of exactly how warm or cold and wet or dry conditions became for the local hominin populations will only be known after the drill cores are analyzed.
At an area on the west side of modern-day Lake Turkana in northern Kenya, another drill core will cover the time period from 2.3-1.4 million years ago. This site would have been in the middle of a vast lake. Nearby, hundreds of artifact sites, fossil hominins and other mammal fossils have been found, including the famous “Turkana boy,” the most complete early hominin ever discovered. At this site, the research team hopes to document how climate change (specifically, increasing aridity affecting East Africa at this time) may have influenced important evolutionary changes observed in the fossil record between 2.3-1.4 million years ago.
Finally, cores from two sites in southern Kenya and southern Ethiopia covering the last 700,000 years will document the period when our species evolved in, and then dispersed out of Africa. This time period saw the appearance of major innovations in human technology (the beginning of the so-called Middle Stone Age) and is also a time of major fluctuations in climate conditions, which may have influenced human evolutionary change and our use of tools.
The team will start drilling in mid-2013 and continue through early 2014.