The artifacts and fossils needed by paleoanthropologists to study and understand the past are embedded in geological contexts where they have often lain undisturbed, protected since burial, sometimes for millions of years.  These deposits are found where sediments that once accumulated are now eroding, in the basins within the Ethiopian Rift Valley and the Afar Depression.  As these sediments were deposited, they piled up and sometimes entombed parts of animals, particularly the bones and teeth that are most resistant to decay.  Under the right circumstances, these hard parts fossilized as the organic components of the bone decayed and were replaced by minerals in the earth.  Artifacts such as stone tools can also sometimes be found in these deposits.  Fossil and artifact bearing deposits are really just a small fraction of all the geological deposits in the region, so a detailed understanding of the past must begin with geological fieldwork.

Geological deposits containing paleoanthropological resources like stone artifacts and fossils are very rare.  In Africa, most of these sites are confined to the rift valleys because it is here that sediments accumulated during the time span of hominid evolution--elsewhere the African continent’s surface is eroding, and little can be preserved for millions of years under these conditions.  In contrast, rift valleys and their lakes and rivers are places that can ‘capture’ evidence from the past and protect it by burial through time.  Because these rift environments are also geological active, the ancient sediments can return to the surface via erosion, exposing their precious antiquities and allowing their discovery by paleoanthropologists.  Modern-day paleoanthropologists are lucky to be living now, at a time when sediments accumulated during the last six million years are being revealed by active geological processes in this dynamic region.

However, even in the best circumstances, these antiquities from the distant past are extremely rare.  Even though the Ethiopian Rift Valley is one of the world’s most important paleoanthropological research areas, its floor offers only relatively small windows of exposed sediment.  In fact, most of the rift floor has no paleoanthropological resources at all.  Rather, the rift floor is mostly covered with recent volcanic rocks like lava flows, or recent soils and flood deposits, large lakes, and pervasive grass cover.  Ancient sediments are exposed only in small patches in the rift.  These patches usually erode from seasonal rainstorms after having been brought to the surface by earth movements (tectonics).  These patches are often called "sites" or "study areas," and the smaller places within them are designated as collection "localities."  Sites can be different sizes.  Some cave sites like Porc Epic are only a few tens of square meters, whereas some large open-air sites such as the famous Omo Shungura Formation in southern Ethiopia are hundreds of square kilometers in extent, with fossiliferous sediments spanning millions of years exposed to modern erosion with each passing rainstorm.

Paleoanthropological sites are found in different ways.  Prior to the late 1980s when Dr. Berhane Asfaw launched a national inventory of Ethiopia, several sites had been found by accidental discovery.  However, the modern approach calls for geologists to use satellite and aerial images to identify potential areas for ground survey (See Figure 1).  This is done by carefully studying the structure of the modern earth’s surface to predict where sediments may have accumulated.  By using the reflectance of ground surfaces recorded by the satellite’s sensors, scientists can identify and target potential study areas.  Ancient sediments that are exposed to erosion on the modern landscape represent good targets for paleoanthropological exploration.  Once such patches of sediment are identified, teams of archaeologists, geologists, and paleontologists visit them in person to assess their potential.

Initial survey of a potential site is conducted carefully, with little collection of antiquities until the geology is understood.  Team members work closely together as they traverse the sediment patches by vehicle and by foot, noting the sediment types and any surface antiquities.  Most exposed sedimentary patches contain no fossils or artifacts.  For those few patches of sediments that do contain these antiquities, it is essential that their position on the landscape and their relationships to the sediment layers and each other be determined precisely.

Fossils or artifacts have little meaning unless their time and space relationships are accurately and precisely recorded at the time of collection.  Today, such collection usually involves using the satellite-based Global Positioning System (GPS) for precise spatial placement.  This technology locates the discoveries geographically, but without providing a time dimension for the finds.  Discoveries may be of very different geological ages, so fieldworkers pay close attention to the vertical ordering of the rock layers in which they are found.  This is a fundamental key to determining the age of the fossils and artifacts.

After the potential of a paleoanthropological study area has been established by survey, a research strategy is developed by the research team.  This strategy is made to match the resources of the study area.  In Ethiopia, a formal permit application is submitted to the Authority for Research and Conservation of the Cultural Heritage, in the Ministry of Culture and Tourism.  The research team must then seek funding from different public and private agencies.  Because paleoanthropology is a non-commercial, scientific and educational enterprise, the work cannot be done as a business.  Rather, basic research is supported by grant support from various agencies such as the U.S. National Science Foundation, the National Geographic Society, the L.S.B. Leakey Foundation, the French CNRS, and the Wenner-Gren Foundation for Anthropological research.

Because of the nature of paleoanthropological research, a long-term approach to work in any study area is most likely to yield the fullest, and most reliable information about the past.  Various specialists in archaeology, geology, and paleontology are assembled in the field to extract different sorts of data necessary to fully explore the past.  For example, there are more than 50 Ph.D. level scientists from a dozen countries working on the Middle Awash study area in the Afar Rift today.  This large team of specialists is led by four co-investigating scientists representing different disciplines: Dr. Yonas Beyene (archaeologist); Dr. Giday WoldeGabriel (geologist); and Professor Tim White and Dr. Berhane Asfaw (paleontologists).  These leaders coordinate the research of the other specialists in the field and laboratory research teams.

Paleoanthropological study areas represent non-renewable resources, and as research work proceeds in the field and laboratory, new questions arise and new research strategies are constantly evolving.  Most of these areas are found in the rift system, and access is often difficult because of poor or undefined roads and a lack of bridges--problems compounded during the rainy season.  Therefore, depending on local climatic conditions, field research is usually scheduled for short periods during the driest months of each year.  The research team usually sets up a field camp from which equipment and scientists are taken by vehicle each day to the excavation or survey sites.  Different specialists working simultaneously on different research problems need different amounts of field time.  Some field sites are remote, and the logistics required to sustain a team in the field operation is a major undertaking, requiring food, fuel, and housing (tents) to be packed and transported in and out.

Each day of fieldwork is different, with parts of the research team undertaking different tasks such as mapping of localities, working with aerial photographs and satellite imagery, collecting fossils, excavating archaeology sites or fossils, sieving with water for microscopic teeth from small mammals like bats and mice, sampling of geological horizons for dating, excavating trenches for sedimentary isotopic studies, and more basic surveying (walking the surface of the sediments and searching for newly-exposed fossils and artifacts).  All of this is difficult and time-consuming work.  This is why research in any one study area can continue for decades.  For example, work in the Hadar and Middle Awash sites has gone on since the early 1970s, and at Olduvai Gorge in Tanzania, excavations have been underway since the 1930s.  All of these projects are still active.  Many of these research study areas will continue to produce important new information as new generations of researchers are trained and become research participants.

The training of future paleoanthropologists is another function of the ongoing research, with students from Ethiopia and elsewhere working closely with senior scientists to learn the techniques, research problems, and field logistics necessary to conduct this kind of research.  One of the most important steps in the process comes when an important hominid fossil has been found.

In paleontological research, contrary to popular belief, paleoanthropologists virtually never find whole skulls or skeletons on the surface.  In general, fossil bone has lost all of its organic matter, and is very brittle.  When fossils reach the actively eroding surface, they tend to shatter into small pieces that are scattered across the outcrop.  Recognizing important fossils under these conditions of erosion, fragmentation, and dispersal is a very specialized activity, requiring detailed comparative knowledge of the skeleton of all kinds of mammals and other vertebrates, as well as local geomorphological circumstances.  When an important fossil is found, the scatter of pieces is assessed and plotted.  Excavations aimed at recovering the rest of the usually fragmentary specimen are then undertaken.  These excavation and sieving operations can last for days or weeks because no effort is spared to recover precious tiny pieces of tooth or skeleton.  Some fossils are found in precarious positions, just eroding out of soft sediment like sand or silt, or on the face of a steep slope prone to collapse.  Such situations require very special extraction techniques designed to rescue the fossil without further damage.  Special chemical consolidation of the fossils is often necessary.

In archaeological research, contrary to popular belief, the paleoanthropologists do not dig at random, hoping to find something interesting.  Rather, they identify likely places to recover artifacts by carefully searching the surface and finding telltale traces of ancient habitation--mostly in the form of bits of bone or stone that have eroded to the surface as witnesses of what is buried below.  As excavation begins, a grid may be established over the site to make sure that each fragment found is plotted precisely.  A complete documentation of what is found on the surface is then completed by the team of excavators.  No clues are overlooked.  As in the paleontological collection, each specimen (stone tools are often called "artifacts") is recorded in field catalogs and later entered into computer databases.