Geologists have identified that the African continent is on track to divide sooner than previously anticipated. An active rift has now hit a “critical threshold,” indicating that it will soon fracture, eventually giving rise to a new ocean.
However, ‘soon’ is relative, as this process will still take a few million more years—a mere blink in geological time.
“We discovered that rifting in this region is more advanced, with the crust being thinner than previously recognized,” says Christian Rowan, a geoscientist from Columbia University.
“Eastern Africa has progressed further in the rifting process than was previously thought.”
The find is particularly intriguing for its historical implications. The Turkana Rift Zone in Kenya is abundant in early hominin fossils, suggesting it was a significant site for human evolution.
Nonetheless, the discovery indicates that this region may not have been more crucial to our ancestors than other parts of Africa. Instead, it might be that these geological processes created highly favorable conditions for fossilization.
While Earth’s current continents appear stable, they are in constant, albeit slow, motion. Over 200 million years ago, they converged to form a supercontinent, and projections suggest they might eventually reunite in the distant future.
Mountains rise where tectonic plates meet, while oceans form where they separate.
The East African Rift System exemplifies the latter. The African plate is currently splitting into two: the expansive Nubian plate to the west, containing most of the continent, and the smaller Somali plate, covering much of the eastern coast and the island of Madagascar.
Scientists concentrated on a specific area of this system for the new study: the Turkana Rift, extending hundreds of kilometers through Kenya and Ethiopia. They examined seismic measurements from the area and determined the crust’s thickness.
The crust is much thinner than anticipated, measuring only about 13 kilometers (8 miles) thick at the rift’s center. In contrast, the crust exceeds 35 kilometers thick along the rift’s edges.
Once the crust in a rift zone thins to less than 15 kilometers, it enters a phase known as ‘necking,’ making a continental breakup almost inevitable.
“As the crust thins, it weakens, promoting ongoing rifting,” says Rowan.
In a few million years, this phase will culminate in oceanization, the formation of a new ocean.
The crust will stretch so thin that magma will erupt from below, forming a basin as it cools. This basin will become a new seafloor, with water rushing in from the Indian Ocean.
This process is already underway in the Afar Depression, located in northeast Africa near the Red Sea.
Researchers estimate that the Turkana Rift began its necking phase about 4 million years ago, following a period of volcanic activity. Interestingly, this period aligns with the age of the earliest hominin fossils found in the area.
The team suggests this is likely no coincidence. As the rift began necking, sedimentation rates increased, providing ideal conditions to preserve records of life from that time.
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“The timing of this tectonic shift and the emergence of thick, fossil-bearing strata suggests the necking phase was crucial for fossil preservation,” the researchers write.
“We propose these tectonic changes were fundamental in shaping the Turkana Rift Zone’s remarkable paleoanthropological record.”
The researchers indicate that further studies could explore this relationship.
The findings were published in the journal Nature Communications.
