Supplementary material to “Connecting Scientific Drilling and Human Evolution”
Published 7 April 2009
Andrew Cohen, Department of Geosciences, University of Arizona, Tucson
Mohammed Umar, Department of Earth Sciences, Addis Ababa University, Addis Ababa, Ethiopia
Citation:
Cohen, A., and M. Umar (2009), Connecting Scientific Drilling and Human Evolution, Eos Trans. AGU, 90(14), 122. [Full Article (pdf)]
Scientific Drilling for Human Origins: Exploring the Application of Drill Core Records to Understanding Hominin Evolution. Workshop Report
ANDREW COHEN, Department of Geosciences, University of Arizona, Tucson, AZ; email: cohen@email.arizona.edu; RAMON ARROWSMITH, School of Earth and Space Exploration, Arizona State University, Tempe, AZ; ANNA K. BEHRENSMEYER, Department of Paleobiology, National Museum of Natural History, Washington, D.C.; CHRISTOPHER CAMPISANO, Institute of Human Origins, Arizona State University, Tempe, AZ; CRAIG FEIBEL, Departments of Geological Sciences and Anthropology, Rutgers University, New Brunswick, N.J.; SHIMELES FISSEHA, Department of Earth Sciences, Addis Ababa University; ROY JOHNSON, Department of Geosciences, University of Arizona, Tucson, AZ; ZELALEM KUBSA BEDASO, Department of Geology, University of South Florida, Tampa, FL; CHARLES LOCKWOOD*, Department of Anthropology, University of Witwatersrand, Johannesburg, South Africa; DANIEL OLAGO, Department of Geology, University of Nairobi, Nairobi, Kenya; RICHARD POTTS Human Origins Program, National Museum of Natural History, Washington, D.C.; KAYE REED, Institute of Human Origins, Arizona State University, Tempe, AZ; ROBIN RENAUT, Department of Geological Sciences, University of Saskatchewan, Saskatoon SK, Canada; JEAN JACQUES TIERCELIN, CNRS, Universitè de Rennes, Rennes, France; MOHAMMED UMER, Department of Earth Sciences, Addis Ababa University, Addis Ababa, Ethiopia
*deceased
This workshop, held in Addis Ababa, Ethiopia considered the role that scientific drilling might play in improving our understanding of the connection between earth history and human origins and evaluated specific drilling targets already under consideration. Relatively simplistic linkages between climate and human evolutionary history have been put forward for over 100 years, but these concepts became much more sophisticated with the advent of detailed climate records from deep sea drill cores. The ability to infer climate variation at a variety of time scales allowed anthropologists to propose new ideas of how Earth history might have influenced hominin evolution. Climate and tectonics (as expressed through change/stability in landscapes, resource abundance and predictability and seasonality) could generate adaptive change, speciation, extinction or stasis in hominin species by affecting species diet, mobility, social strategies, reproduction and demography. Testing linkages from the earth science side requires records from various locations and time intervals encompassing a range of biotic “events” (including intervals of stasis as well as change). Computer modeling experiments on the interaction of climate and ecosystem change would also provide critical tests of hypothesized links between human evolution and Earth history.
Prior studies had given us a general rationale for drilling hominin fossil sites. An East African Rift focus for an initial drilling program is most likely to yield immediate scientific benefits at a reasonable cost. Lake beds with the combined attributes of high sedimentation rates, temporal continuity, good geochronologic control, close proximity to fossil/artifact sites, and ease of truck-mounted drill rig access (an important cost consideration) are fortunately present in several areas of the rift valley.
An exploratory NSF grant allowed the steering committee to characterize four promising locations for a first phase of drilling, encompassing a range of critical time intervals for hominin evolution and types of drilling targets. Site studies consisted of logistical evaluations (road and water access for drill rigs, consultations with local drillers and stakeholders) and limited subsurface geophysics (reflection seismics, electrical and magnetic surveys). The workshop provided an opportunity to review the results of these surveys, as well as to consider other promising drilling targets.
One potential target is a large Pliocene paleolake depocenter in the northern Awash River valley (Afar region) of Ethiopia. The site, known as Ledi Geraru, is in the same depositional basin as some of the most important accumulations of Middle Pliocene hominin fossils in the world, including the Australopithecus afarensis fossil “Lucy”, the “first family” collection of A. afarensis fossils and the earliest known stone tools. With its thick sequence of fine-grained lacustrine sediments, including diatomites, this site could provide an excellent >3.4–2.9 Ma paleoclimate record, encompassing an interval of both morphological stasis and change for A. afarensis.
Another promising drill site lies on the west side of Lake Turkana, Kenya, in the depocenter of an early Pleistocene (~2–1.5Ma) predecessor of the modern rift lake. The region is renowned for its archaeological, hominin and other vertebrate fossil record, including over 500 hominin fossils and 100 archaeological sites. As with the Afar area, establishing an age model for the thick lacustrine sequence to be cored would be facilitated by the numerous dated and characterized tephras. A high resolution paleoclimate record here would span the time of the origin of several species of Homo, the earliest Acheulean stone tool technology, and the first dispersal of hominins out of Africa.
Two sites in southern Kenya would provide records of more recent events in hominin evolution. The Olorgesailie Basin was occupied by a paleolake between ~1.2–0.5Ma, and contains some of the most important middle Pleistocene (Acheulean) archaeological sites in the world, along with abundant vertebrate fossils. As with the other areas discussed, it has well dated tephras throughout the lake beds that would be targeted for drilling. Nearby Lake Magadi, a playa in the sump of the Kenyan rift valley is also promising. Earlier trona exploration drilling and geophysical surveys revealed a thick sequence of lacustrine sediments spanning the last million years. Combining core results from the Olorgesailie and Magadi basins would allow researchers to distinguish intrabasinal hydrologic events from regional climate history, address hypotheses about water and food resources for hominins at a variety of time and spatial scales, and consider environmental history during the emergence of Homo sapiens.
Additional sites in Kenya and Ethiopia were also considered (e.g. near Lakes Baringo and Chew Bahir) during the workshop and following the meeting a call was put out to the scientific community for additional site suggestions (Hominid Sites and Paleolakes Drilling Project). Many hominin fossil and archaeological sites would benefit from adjacent lake bed drilling and the workshop participants recognized that any drilling campaign to arise from this meeting should only be a first phase in what could emerge as an entirely new arena for scientific drilling. Much of the meeting discussion time was devoted to considering the science/logistical issues surrounding each area, and strategies for core sampling, analysis, curation and logging. By the end of the meeting a consensus had emerged that a project review committee should move ahead with a formal evaluation of all proposed sites, along with an analysis of funding options for the project.
