Researchers have reported that the Earth's crust in the region known as the "Turkana Rift" in East Africa has become significantly thinner, which could eventually lead to the splitting of the African continent.
This discovery could offer a new explanation for why this region contains the richest fossil record of humankind.
The Turkana Rift is a unique geological region in East Africa and a vital part of the Great Rift System. A wide, low-lying area stretching 500 kilometers across Kenya and Ethiopia, the Turkana Rift is a hotspot for discovering fossils of our early ancestors and is also volcanically active due to tectonic plate movement.
This region is part of the larger East African Rift System, where the African Plate is moving away from the Somali Plate at a rate of about 4.7 mm per year, causing the Earth's crust to expand horizontally, crack, and release magma from the depths.
- To what extent has the Earth's crust become thin?
Along the fault axis, the rock crust is only about 13 kilometers thick, compared to more than 35 kilometers in areas far from the fault center. This large difference is a hallmark of a geological process called "necking".
Researcher Christian Rowan, a doctoral student at Columbia University, says the narrowing process is like a salty toffee that is pulled at both ends, so the middle becomes thinner and longer while the ends remain the same.
As the crust thins, it weakens, and this weakness contributes to continued expansion and cracking until the crust eventually breaks. Geophysicist Anne Bissell confirms that the region has "reached a critical point," making it more susceptible to fracturing.
But this is not a cause for concern now because it will happen according to geological time, that is, after millions of years.
The Turkana Rift began forming about 45 million years ago. The "thinning" phase began after massive volcanic eruptions about 4 million years ago. It will take a few million more years before this thinning transitions to an "oceanization" phase, where magma will surge through the fissures to create a new seafloor, which will then be filled by water from the Indian Ocean coming from the north.
The researchers found evidence of an earlier period of rifting that occurred millions of years ago, but which did not lead to the continent's breakup. However, that period left the Earth's crust weaker and thinner, which facilitated the current rifting phase. This discovery, says Rowan, "challenges some conventional ideas about how continents break apart."
The Turkana Rift is the first active continental rift identified as undergoing a thinning phase. Co-author Flarin Kolawole says, "We now have a front-row seat to observing a critical rifting phase that has shaped all rift margins around the world." Understanding these processes helps scientists reconstruct past landscapes, vegetation, and climates, and then use that knowledge to understand what the future holds.
Here comes the most exciting part. Scientists have long wondered: why does the Turkana Rift Valley contain such a huge number of fossils of our ancestors, with more than 1,200 human fossils dating back four million years being found, which is a third of all human fossils in Africa.
The researchers say their findings point to a new answer: After massive volcanic eruptions about 4 million years ago, a thinning process began, causing the land to sink and leading to a rapid accumulation of fine sediments. These sediments were ideal for preserving and protecting fossils.
In other words, the Turkana Rift may not have been unique in its importance to the evolution and diversification of our ancestors, but was simply a place that provided ideal conditions for documenting this evolution.
As Rowan explains: "The conditions were right for maintaining a continuous fossil record."
This is still just a hypothesis, but the researchers hope that their colleagues will be able to use these findings to explore the relationship between tectonic plate movements and climate change and their impact on human evolution.
The detailed study was published in the journal Nature Communications on April 23 .
