Two important areas in east Africa have provided the best evidence of this very early hominid. Hadar is located within the Afar Triangle of northeastern Ethiopia at the north end of the Rift Valley. Dating of the geology of the area indicates fossils from Hadar date to the period between 3.5 and 3.0 m.y.a. Hadar is located within the Afar Triangle of northeastern Ethiopia at the north end of the Rift Valley. Dating of the geology of the area indicates fossils from Hadar date to the period between 3.5 and 3.0 m.y.a. Two extraordinary finds from Hadar include "Lucy" and the "First Family". Lucy was a 40% complete skeleton and the First Family represented 13 individuals possibly from one social group that was caught in a flash flood. Hadar hominids form the basis for definition of A. afarensis as a group. Recent dating of the Lucy find has been placed A. afarensis at 3.16 m.y.a.

Laetoli is located in northern Tanzania. Using the volcanic sediments, paleoanthropologists believe that Laetoli remains date between 4.0 and 3.5 m.y.a. In 1978, Mary Leakey found the well-preserved footprints of several hominids. These date to approximately 3.75 m.y.a. This implies that A. afarensis probably lived for nearly a million years. It is important that over this time there was little change in the nature of A. afarensis.

Recent finds in Chad suggest that A. Afarensis may have lived outside of the Rift Valley. This opens up questions such as where this Hominid may have developed although finds in southern Ethiopia suggest a pre-hominid may have lived to the north of the Hadar region.

As the Great Rift valley of east Africa formed about 6 million years ago, cooler climatic conditions developed. These shrank humid forest areas creating scattered forests and savannas (grasslands). This had profound impacts on primates as well as other mammals living in the region. The apes that clung to the scattered patches of humid forests began a slow decline that has led them toward extinction today. Apparently, some apes adapted to the changing conditions and moved toward the savannas. How this relates to the development of bipedality is unclear, but bipedal forms would have had an advantage in walking across savannas for a number of reasons. Clearly, one could see dangers by being upright and eventually walking long distances could have become more a more efficient means to travel.

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