April 20, 2017
6pm in ASB 220
Featuring: Francis H. Brown, Department of Geology & Geophysics, University of Utah
Lake Turkana was the last major lake in East Africa to become known to Europeans. The arid basin in which it is located has been studied since ~1900. Sedimentary deposits there contain a fossil record stretching from the Cretaceous to the late Pleistocene. Recent work in the basin began in 1966 as a prelude to the International Omo Research Expedition with teams from the U.S., France, and Kenya, and has continued since.
The Omo-Turkana basin has yielded the only Cretaceous dinosaurs and other reptiles from East Africa, type specimens of the Miocene primates Afropithecus, Kamoyapithecus, Turkanapithecus, early evidence of bipedalism in Australopithecus anamensis (4.1 Ma), the oldest record of stone tools (3.3 Ma), the earliest Paranthropus boisei (2.5 Ma), the remains of Homo rudolfensis (2.0 Ma), the most complete skeleton of Homo ergaster (1.5 Ma), the earliest known Homo erectus (1.9 Ma), the oldest known Homo sapiens (195 ka), and type specimens of many other mammalian and reptilian genera. Because these fossils are found in sequences with volcanic rocks, they are well dated.
The Int’l. Omo Research Expedition, the brainchild of F. Clark Howell, marked the beginning of systematic work in paleoanthropology (study of the evolutionary and cultural history of humankind and near relatives). It was the first expedition to insist on stratigraphic knowledge before fossils were collected, the first in the region to use aerial photographs for fossil locations, the first to create a computerized database of fossils (still in use), and the first to establish the modern ecology of the region and to collect the modern pollen rain. It took advantage of then new dating techniques (K/Ar; paleomagnetic stratigraphy), and it trained many workers who moved on to other areas using similar techniques.
Over the 50-year period of study, technological advances have made it possible to date materials that then could not handled. Isotopic studies (largely initiated by Thure Cerling) allowed determination of plant cover at ancient times, determination of diets of various animals (including early human relatives), estimation of ancient soil temperatures, and estimation of water deficit through time. Seismic and gravity work for oil exploration begun in the late 1980s has provided a wealth of information about the deep structure of this basin.
Fifty years ago paleontological sites separated by great distances (10–1000 km) were treated independently, but many of these sites are now related through geochemical correlation of volcanic ash layers. Some of these ash layers are found in deep-sea deposits of the Indian Ocean and the Gulf of Aden, allowing importation of climatic data to the fossil sites. Climatic information from sapropels in the Mediterranean Sea confirms the times of more recent depositional episodes (10–200 ka) which preserve fossils of early Homo sapiens.