Great Rift Valley

The Great Rift Valley is a historically significant geographic region in southwestern Asia and eastern Africa that, since the early twentieth century, has yielded some of the most important scientific and archaeological fossil discoveries that shed light on the origin and evolution of humankind. Consequently, certain regions of the Great Rift Valley extending from Ethiopia to Tanzania have been termed the birthplace of humanity. The Great Rift Valley is actually a system of rift valleys, or valleys formed through tectonic movement, comprising the Jordan Rift, Red Sea, and East African Rift Valleys. The entire system is approximately 4,800 kilometers in length; however, although it extends from Syria (in the Middle East) to Mozambique (in southeastern Africa), the portion of the Great Rift Valley that receives the most scientific attention is the branch of the East African Rift Valley between Ethiopia and Tanzania. Several well-known archaeological excavation sites are found throughout the Great Rift Valley, such as the Olduvai Gorge in Tanzania, as well as Hadar and the Middle Awash, both in Ethiopia. The valley formed approximately twenty to thirty million years ago and is also a region of interest to geologists; the area is home to some well-known volcanoes such as Mount Kenya and Mount Kilimanjaro, as well as a diverse array of animal life. As just one example, the Kenya Lake System region of the Great Rift Valley (comprising three shallow lakes—Lake Bogoria, Lake Elementaita, and Lake Nakuru) features more than a dozen endangered species of birds.

Background

The shifting of African and Arabian tectonic plates away from one another on the Earth's surface layer twenty to thirty million years ago created the Great Rift Valley. The drifting of these plates produced a crack in the Earth’s top layer, resulting in a “cavity” that dips to the Earth’s second layer of crust. This “cavity” is the Great Rift Valley, which is 4,800 kilometers in length. The East African Rift Valley, the most famous portion of the Great Rift Valley, consists of two fault lines that straddle the eastern and western sides of Africa’s Lake Victoria, which stem from tectonic plate shifting. Within Africa, the eastern fault line passes through the nations of Ethiopia, Kenya, and Tanzania, while the western fault line passes through Uganda, Rwanda, and the Democratic Republic of the Congo. The Great Rift Valley features various geographic and geological terrains, including mountainous highlands, pastoralist lowlands, savannas, and deserts. This geographic diversity has resulted in a wide range of cultural diversity amongst the various peoples who inhabit the Rift Valley region.

Overview

The Great Rift Valley is an area of extreme interest to archaeologists and physical anthropologists, as several significant findings of hominid (humanlike ancestor) remains have been discovered in this region. The generally basic nature of the valley’s soil greatly helps preserve fossilized bones for long periods, thus enhancing the scientific community’s ability to trace the history of the hominid lineage.

In November 1974, an excavation team directed by US anthropologist Donald Johanson made one of the most famous fossil findings in history when it discovered the remains of a female hominid dated to approximately three million years ago on the outskirts of Hadar, a village in Ethiopia along the Great Rift Valley. What made Johanson’s discovery all the more remarkable was the fact that an almost entirely complete skeleton was found at the site, including the cranium, ribs, arm, digits, pelvis, and legs—as opposed to merely a few fragments of a skull or jaw, which is far more common in hominid fossil recoveries. Johanson’s team named this fossil “Lucy” after the Beatles’ song, “Lucy in the Sky with Diamonds.” Subsequent analysis of Lucy revealed that she may be the ancient ancestor of the genus Homo, of which modern humans (Homo sapiens) belong. Lucy stood approximately three-and-a-half feet tall, and her pelvis indicated that she was capable of walking upright on two legs—a feature not found in chimpanzees or gorillas, the closest relatives to modern humans. However, Lucy’s head and face more closely resembled that of apes rather than modern humans, although Lucy had much smaller teeth than apes. Scientists later named the species to which Lucy belongs Australopithecus afarensis, or “the southern ape of Africa.” No stone tools or weapons were discovered with Lucy or other A. afarensis sites, leading scientists to conclude that the species likely lived as scavengers.

Scientific research has further revealed that the major periodic fluctuations in climate within the Great Rift Valley over the past two million years may have significantly shaped human evolution, particularly in developing larger, more complex brains. In 2013, a study by British scholars Mark Maslin, a geographer, and Susanne Shultz, a physical anthropologist, found that the points in history marked by significant increases in hominid brain size correspond to points in history marked by significant shifts in environmental climate within the Great Rift Valley. Some of these shifts in climate include periods of heavy rainfall, which resulted in the formation of numerous lakes and the growth of thick vegetation, while at other points in history, the valley experienced reduced levels of rainfall (perhaps including droughts), which resulted in the drying up of lakes, a significant loss of vegetation, and the formation of deserts. Such dramatic climactic transitions would have increased the urgency for hominids to adapt to the changing circumstances, thus forcing innovations in culture, diet, and technology that would have favored the evolution of larger, more complex brains through natural selection.

Although geneticists completed sequencing the human genome in 2003, knowledge of the human genetic code is still in its infancy—although scientific knowledge of deoxyribonucleic acid (DNA) has rapidly increased. Ongoing genetic, archaeological, and geological research continues to provide insight into the hominid lineage and human prehistory, of which the Great Rift Valley continues to demonstrate its importance in human evolution.

In 2023, researchers in the Jordan Rift Valley, part of the target Great Rift Valley system, found evidence of tool-making societies along key migration routes believed to have led early peoples out of Africa. Studies of this area have also found that while once presumed to be desert, the environment once contained savannas and grasslands, allowing early humans to survive these migratory treks from Africa to other areas of the world, such as southwest Asia. These discoveries provided insight into the interplay between climate, migration, and evolution. Further, the Great Rift Valley continued to offer valuable fossil finds that further informed this research. Finally, understanding the geographical shifts and climate events that took place in the Great Rift Valley throughout Earth's history helps modern scientists to better understand and make more informed decisions regarding global climate change.

Bibliography

Gilbert, Elizabeth. Tribes of the Great Rift Valley. New York: Abrams, 2007.

Johanson, Donald C. Lucy’s Legacy: The Quest for Human Origins. New York: Three Rivers, 2010.

Kennedy, Adam Scott. Birds of Kenya’s Rift Valley. Princeton: Princeton UP, 2014.

Kristof, Emory. "Rift Valley." National Geographic Education, 4 Jan. 2024, education.nationalgeographic.org/resource/rift-valley. Accessed 6 Oct. 2024.

Meredith, Martin. Born in Africa: The Quest for the Origins of Human Life. New York: PublicAffairs, 2011.

Mkutu, Kennedy Agade. Guns and Governance in the Rift Valley: Pastoralist Conflict and Small Arms. Bloomington: Indiana UP, 2008.

Orf, Darren. "New Discovery May Help Predict When Africa Will Split in Two." Popular Mechanics, 26 July 2023, www.popularmechanics.com/science/environment/a44189729/east-african-rift-deformations. Accessed 6 Oct. 2024.