Home Sciences They discover inexplicably ancient rocks under the sea: 2,700 million years

They discover inexplicably ancient rocks under the sea: 2,700 million years


Scientists have just released a discovery that could change the current view of how tectonic plates work. To the south of Africa They have found the oldest rocks ever found on the seabed, 2.7 billion years old, which also seem to come from the neighboring African continent. They did not expect to find rocks of such age in a relatively young place: “It’s like finding a mother in a kindergarten,” say the researchers from the Chinese Academy of Sciences.

Between the Earth’s rigid tectonic plates and the convective mantle is a hot, soft layer known as the asthenosphere, which ranges from 40 to 660 kilometers deep. At mid-ocean ridges, basalt from the hot asthenosphere extrudes toward the seafloor surface.forming a new oceanic crust and renewing the seabed.

Over time, that new oceanic crust ages, cools, and becomes denser. But when this material meets an obstacle, such as a continent, it sinks under it, thus returning the matter from the bottom to melt within the asthenosphere and return to the mantle deeper, a phenomenon known as subduction. Because of this, oceanic crust is typically less than 200 million years old.

However, something has been found that does not fit. A joint research team, led by Professor Liu Chuanzhou from the Institute of Geology and Geophysics (IGG) of the Chinese Academy of Sciences, has found abyssal peridotites from the seafloor along the southwestern ridge of the Indian Ocean, specifically south of Madagascar. This is a surprise, because they are the oldest rocks ever discovered in the ocean. A later study revealed that in fact come from the neighboring African continent. This work was published in Science Advances this very week.

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These newly discovered rocks in the Indian Ocean are 2.7 billion years old and date back to a period of time geologists call ‘Archaean’, which comes from the Greek word for ‘ancient’. They are too old to be there. As an analogy, the appearance of these ancient rocks in a young mid-ocean ridge “is like finding a mother in a nursery school,” according to the scientists. These incredibly ancient mid-ocean ridge rocks offer a clue to their mysterious origins.

Rocks typical of the continents, not the ocean floor

Furthermore, these ancient rocks have strongly refractory compositions; in geochemistry, refractory denotes a lack of fusible (ie easily melted) components in the mantle. Therefore, they are less like the materials found in the oceans and more like the rocks that make up the continents.

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How is this possible? The only explanation for this, according to the authors of the work, is that these rocks from the archean mantle of the Indian Ocean would have broken off and been transported through the asthenosphere over 2,000 km to the mid-ocean ridge where they have been discovered.

To test whether this geological recycling mechanism is really valid, computer simulations were performed. And indeed, the results obtained suggest that this recycling process was highly efficient. In fact, up to 20% of the continent could be removed under water in just 100 million years, which, from a geological perspective, is the blink of an eye.

Ancient continental debris found on the ocean floor clearly indicates that oceanic plates have a more complicated functioning than previously thought previously.

“Therefore, to decipher the evolution of the Earth, more attention should be paid to the bottom of the oceanwhich covers three-fifths of the earth’s surface,” the researchers explained.

The study was conducted in collaboration with the Woods Hole Oceanographic Institution and the Max-Planck Institüt fur Chemie.

Reference research: https://www.science.org/doi/10.1126/sciadv.abn6749


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