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A new study from the University of Texas at Austin has demonstrated a possible link between life on Earth and the movement of continents. The results show that sediments, often consisting of pieces of dead organisms, could play a key role in determining the rate of continental drift. In addition to questioning existing ideas about plate interaction, the results are important because they describe potential feedback mechanisms between tectonic movement, climate, and life on Earth.
The study, published on November 15 in Letters of Earth and Planetary Science, describes how sediment moving under or subducting under tectonic plates could regulate plate movement and could even play a role in the rapid rise of mountain ranges and the growth of the continental crust.
The research was conducted by Thorsten Becker, professor at the UT Jackson School of Geosciences and researcher at the Institute of Geophysics (UTIG), and Whitney Behr, researcher at the Jackson School and professor at ETH Zurich in Swiss.
Sediments are created when wind, water and ice erode existing rocks or when shells and skeletons of microscopic organisms like plankton accumulate on the seabed. It has long been known that sediments entering subduction zones have an influence on geological activity, such as the frequency of earthquakes, but it was thought until now that its influence on the movement of the continent was weak. Indeed, it was believed that the speed of subduction depended on the strength of the subduction plate when it bent and slid into the viscous mantle, the layer of semi-molten rock beneath the earth's crust. The continental movement is driven by a plate sinking under another, so that, in this scenario, the strength of the part of the plate drawn into the Earth's mantle (and the energy needed to bend it) would constitute the main control of the speed of the plate. movement, sediments having little effect.
However, previous research involving scientists from the UTIG had shown that subduction plates could be weaker and more sensitive to other influences than previously thought. This led the researchers to look for other mechanisms that could affect the speed of the plate. They felt how different types of rocks could affect the interface between the plates – the boundary between the subducting plates. Subsequent modeling has shown that sediment rock can create a lubricating effect between plates, accelerating subduction and increasing plaque velocity.
This mechanism could trigger a complex feedback loop. As the speed of the plate increases, there will be less time for the sediments to accumulate, so that the amount of sediment in subduction will be reduced. This leads to a slower subduction, which may allow the mountains to develop at the edges of the plates because the strength of the two plates that meet causes an uplift. In turn, the erosion of these mountains by wind, water and other forces can produce more sediment that reintroduces into the subduction zone and restart the cycle by increasing the speed of subduction.
"The feedback mechanisms are used to regulate subduction velocities so that they do not" pack up "with extremely fast speeds," Behr said.
The new model of Behr and Becker also offers a compelling explanation for variations in plate rotation speed, such as the dramatic acceleration of northern India some 70 million years ago. The authors suggest that, when India crossed vibrant equatorial seas, an abundance of sedimentary rocks formed by organic matter settling on the seabed created a lubricating effect in the subduction plate. The north walk of India has gone from 5 centimeters a year (about 2 inches) to 16 centimeters a year. As the continent accelerated, the amount of sediment being subducted decreased and India slowed down before finally colliding with Asia.
Behr and Becker suggest that these feedback mechanisms would have been very different at the beginning of the Earth before the formation of the continents and the emergence of life. Although their model does not examine the origins of these feedback mechanisms, it raises compelling questions about the interaction between the continental movement and life on Earth.
"What is becoming obvious is that the geological history of the incoming plate is important," said Becker, who is also the Shell Chair in Geophysical Science at the University of Ottawa. UT. "We will have to study in more detail how these possible feedback processes might work."
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