The gravitational interaction between Earth, Moon and Sun would be responsible for the dynamics of tectonic plates on our planet, as suggested by a study led by Washington University. Until then, convection currents in the planet’s hot core were the likely explanation for the movement of the Earth’s crust.
The movement of tectonic plates is what shapes the entire surface of the Earth. Until now, these large blocks of the lithosphere were thought to be exclusively pushed by convection currents from the mantle in deeper layers, but the new study suggests one more factor in this dynamic.
Convection alone would not produce enough force to shift tectonic plates, according to the authors of the new study. Instead, the gravitational force between the Earth, Moon and Sun would be the main driver for their displacement.
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The explanation would be the barycenter of the Earth-Moon system — the point at which the two orbit — which is not exactly at the Earth’s center of mass, the geocenter. Due to the gravitational attraction of the Sun, the centroid changes by up to 600 km throughout the month.
Geophysicist Anne Hofmeister, lead author of the study, explained that since the oscillating barycenter is 4,600 km from the geocenter, Earth’s orbital acceleration and solar attraction are unbalanced, except at the barycenter. The lithosphere, then, would not withstand all this tension and would break, forming the plates.
In addition, the rotation of the Earth would contribute to the increase of these tensions in its interior. When combined, all these divergent forces produce the shifting and fragmentation of tectonic plates.
In other words, the solid lithosphere and upper mantle are being rotated at different speeds due to gravitational stresses, but solely thanks to the unique configuration of the Earth-Moon-Sun system.
According to Hofmeister, our exceptionally large Moon and the distance to the Sun are critical. Without this natural satellite, there would be no variation between the barycenter and the geocenter; therefore, there would be no tectonic movements.
Still, the authors highlighted that the hot interior of the Earth is fundamental for the functioning of all this dynamics. “The Earth’s interior heat is essential to create the thermal and physical boundary layer known as the lithosphere,” the team pointed out.
The same was applied to other rocky bodies in the Solar System, but none show confirmed tectonic activity. A strong candidate for further study would be Pluto, which, despite being small and cold, has a huge moon and a young surface, Hofmeister pointed out.
The study was presented in the journal GSA Special Papers.
