The Sun, the Moon and the movement of the continents

The Sun, the Moon and the movement of the continents


A new hypothesis challenges the belief that it is the convection of the Earth’s mantle that is responsible for plate tectonics, which move due to gravitational interaction with the Moon and the Sun.

Inside the Land, everything moves. From the outer core, which spins rapidly around the inner core, made of molten iron and nickel, to the mantle, the thick, viscous layer of rock over 3,000 kilometers thick whose convection movements set in motion plate tectonics and the movement of the continents… or at least that is what was thought until now.

Now, a team of geologists from Washington University in St. Louis, led by Anne M Hofmeister, has just proposed a totally new hypothesis about the internal dynamics of the Earth. One according to which it would be the gravitational interaction with the Moon and the Sun, and not the internal heat of the planet, which moves the Earth’s mantle.

In a special article in the Geological Society of America, the new analysis provides an alternative to the hypothesis that tectonic plate motion depends on convection currents in the mantle. Convection involves the increased buoyancy of hot fluids, but Hofmeister and his colleagues argue that doesn’t apply to solid rocks. According to the researchers it is force, not heat, that moves larger objects. And that force arises from gravity.

a new theory

The most accepted theory about the functioning of the Earth dictates that its internal movements depend on the dissipation of heat generated by radioactivity and by the energy left over from ancient collisions from the times when our planet was formed. But even the staunchest proponents of mantle convection acknowledge that that amount of internal thermal energy is insufficient to drive large-scale tectonics.

However, Hofmeister and his colleagues argue that Earth’s plates could be shifting because the Sun exerts such a strong gravitational pull on the moon that it has caused its orbit around Earth to lengthen.

Over time, the position of the barycenter, the center of mass between Earth and the Moon, has moved closer to the Earth’s surface and now oscillates about 600 kilometers per month relative to the geocenter, Hofmeister said. Which generates internal tensions, since the Earth continues to rotate.

“Because the oscillating barycenter is about 4,600 kilometers from the geocenter, the Earth’s orbital tangential acceleration and the solar pull are out of balance, except at the barycenter Hofmeister explains. The planet’s warm, thick, strong interior layers can withstand these stresses, but its thin, cold, brittle lithosphere responds by fracturing.”.

The daily rotation of the Earth is also flattening the planet, which is not a perfect sphere. and that also contributes to the brittleness of the crust. Together, these two independent stresses have created the patchwork of plates seen in the outer shell of our planet. According to the authors of the research, the variety of movements of the plates comes from the changes in size and direction of unbalanced gravitational forces over time.

The sun and the moon

But how to test this hypothesis? Hofmeister suggests that “one test would be a detailed examination of the tectonics of Pluto, which is too small and cold for convection but has a giant moon (like us) and a surprisingly young surface.”

The study includes a comparison of Earth with the various rocky planets of the Solar systemfrom which it follows that the presence and longevity of volcanism and tectonism depend on a particular combination of factors: the size of their moons, their orbital orientation, proximity to the Sun, and the rates of rotation and cooling of each planet.

According to Hofmeister, Earth is the only rocky planet with all the factors necessary for plate tectonics. “Our exceptionally large moon and the particular distance from the Sun says the researcher are essential».

Font: Jose Manuel Nieves / ABC

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Written by Editor TLN

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