Jon Kalb:   Rift valleys are immense cracks or elongated depressions in the earth's surface. They're formed by the upwelling of magma (molten rock), which causes the separation and uplift of landmasses on either side of the rift. When the magma reaches the surface it does so in the form of lava flows or volcanoes. Rivers flowing into the rifts from the now adjacent uplifted highlands carry with them sediment that accumulates on the floor of the rift, often to great thickness. Any animal remains, including human ancestors, or archeological remains, are quickly buried by sediment and over thousands or millions of years form thick successions of fossil- and artifact-bearing strata.

When the strata are once again exposed to the surface by erosion from modern rivers or faulting, and because much of eastern Africa is so arid, these remains stay preserved for some years before they deteriorate. Famous hominid (from Hominidae, humans and their immediate ancestors) sites such as Olduvai Gorge in Tanzania and Lake Turkana in northern Kenya, both in the East African Rift, are the result of such histories. This raises an important point: it is not necessarily the case that human ancestors originated in eastern Africa, rather geological and arid climatic conditions have preserved their remains in rift valleys. The same reasoning applies to the preservation of fossils in cave deposits in southern Africa. As far as we know, it is just as likely that proto-humans may have originated in the Congo, but because it is primarily rain forest, fossil remains are not preserved.

As I mentioned earlier, the Afar Depression was created as a result of the intersection of three rift valleys forming what geologists call a "triple rift junction." These rifts are the Red Sea and the Gulf of Aden, whose landward extensions formed the northern and eastern Afar, and the East African Rift (in Ethiopia the "Main Ethiopian Rift"), which created much of the southern Afar. The result of this multiple rifting is the collapsed lowlands of the Depression. Flowing through the Afar is the Awash River, which travels through the three rifts of the triple junction (and is the only such river in the world). Today the Awash and its many tributaries dump massive amounts of sediment eroded from the highlands onto the Afar floor--by analogy such deposition in the past accounts for the thick fossil- and artifact-bearing strata in the Middle and Lower Awash that have accumulated over millions of years. Interestingly, fossil hominids have been found in all three of the triple junction rifts--near Massawa in the far north, in Djibouti to the east, at Galila in the far south, and of course throughout the western and central Afar.

Jon Kalb:   The most common dating methods are based on the constant rate of decay of naturally occurring radioactive minerals, most often found in volcanic rocks or sediments, such as volcanic ashes or tuffs. These are clock-like dating methods performed in laboratories and can be extremely accurate. If a volcanic layer is dated radiometrically at 3.5 million years and a layer above it is dated at 3.3 million years, then it can be assumed that any fossils found between these layers are very close to 3.4 million. There is also a form of dating called faunal or relative dating. If a certain faunal assemblage is dated radiometrically in the Omo Valley, at say, 2 million years, and if you find that same assemblage at a level in the Middle Awash, you can then say that the Afar fossils "relative" to those in the Omo are approximately the same age, 2 million years. Lacking radiometric dates at the time, the dates for sites that my colleagues and I arrived at were estimated in this manner, and proved to quite accurate in most cases.

Jon Kalb:   Most definitely. Unfortunately, greed, ambition, and territoriality are the ingredients that infect much of the work in paleoanthropology, and, to be fair, in other fields as well. But the problems in paleoanthropology are accentuated because of the rarity of the finds and the enormous rewards that come with discoveries.

Jon Kalb:   Tremendous in all categories. For an overview, I suggest Virginia Morell's book, Ancestral Passions (Simon & Schuster,1995). Since this book was published, more great discoveries have been made in Kenya by the Leakey team, and others.

Jon Kalb:   The term is one that was widely popularized by the British explorer, Henry Stanley, in the late 19th century in his books, Through the Dark Continent(1878), In Darkest Africa (1890, and My Dark Companions (1893). Besides the obvious ethnic sense of the term, Stanley spent much of his time deep in the Iture rain forest exploring the Congo basin without seeing the sun for days or months at a time, while also suffering the "darkest" deprivations of starvation, sickness, and the death of his men. Thus, he may have come up with the term "dark continent" for multiple reasons. In my book I refer to Stanley and his work as a motif or theme, usually in the form of an overstatement to highlight certain points. By the way, Stanley began his career in Africa as a journalist covering the British-Emperor Teodros confrontation at Magdala, and its tragic ending. Unfortunately, Stanley ended his career helping King Leopold of Belgium put together the "Congo Free State." To Stanley's credit he was far less a racist than many in his day, and he had no idea of the diabolical lengths to which Leopold would go to profit from the Congo.

Jon Kalb:   First, its a great discovery and I congradulate them. We learn that their team discovered 17 fragmentary teeth and bones of a very early human ancestor. The fossils come from the lower Adu-Asa Formation along the western margin of the Middle Awash, and are approximately 5.5 million years old. This makes them about one million years older than the next oldest hominid found in the central Middle Awash, at Aramis in the Sagantole Formation. In addition to its great age, kadabba is more ape-like than the Aramis fossils, but more human-like than chimps. These differences are distinguished by a number of dental characters (which no doubt will be seen to be more unique when more of the fossil is found). A toe bone suggests kadabba was bipedal, or walked upright. These distinctions and its great age probably means that a biology teacher in the Ukraine will soon rename kadabba as a new species (as opposed to the more refined subspecies label the name now represents).

From the geology, we learn that the setting of the kadabba fossils, similar to that at Aramis 4.4 million years ago, was a relatively humid, wooded environment at an elevation well above the present-day Awash River. Both the Adu-Asa and greater Aramis areas were also subjected to periods of intense tectonic and volcanic activity. In the Adu-Asa area, this activity led to the drainage of a large lake that had existed for some duration, which was replaced by the woodlands that were inhabited by hominids and other animals.

If the Aramis/Adu-Asa hominids were bipedal and lived in a wooded or forested environment, this contradicts long held theories that hominids began walking on two legs as an adaptation to a regional, climate-induced reduction of the forests, that drove our bipedal ancestors out of the woods and into the open savannas to forage for food. Instead, assuming the Berkeley paloenvironmental data is correct, it's apparent that the "bipedal apes" from the Middle Awash were two-legged long before they left the forests, for some one million years or more. So why then did these creatures become bipedal? This is a question still to be answered.

A final point: In the interest of science, Haile-Selassie, WoldeGabriel, and their colleagues might have noted that the RVRME did far more in the Adu-Asa area(as at Aramis) than simply assign "Lithostratigraphic units...to the Awash Group" (Nature,412:176), rather from 1982 to 1993 we published maps in 7 international journals, including Nature (298:20), showing the location of the fossil-bearing units that produced the Adu-Asa hominids, as well as the location of 4 of the 5 fossil localities where hominids were actually recovered (412:181,"Localities"). These same localities are also described in my book (pages 197, 200-202, 208, 245).

Jon Kalb:   I would refer your readers to my suggestions on pages 306 and 307 of my book. Otherwise, while attending scientific meetings over the last few months, I've had the pleasure of meeting a number of young scientists, both Ethiopian and foreign, who in recent years have worked at Hadar or in the Middle Awash. I was impressed by their openness and fresh outlook. I would look to this generation for answers to Ethiopia's future in prehistory research--I wish them and the Ministry of Culture the best of success.

Jon Kalb:   I've heard rumors that an effort is being made to host the leaders of the research teams currently working in Ethiopia for purposes of cooperation and possible collaboration. It sounds like a good idea.