Tug of sun, moon could be driving plate motions on ‘imbalanced’ Earth

A study led by Anne M. Hofmeister at Washington University proposes that the Earth-moon-sun system drives the circulation of the mantle.

There is an alternative to the hypothesis that the movement of plates is related to the currents in the Earth's mantle. Hofmeister and her colleagues argue that convective rise of heated fluids does not apply to solid rocks. They argue that force moves large objects. The new research was published in a special paper by the Geological Society of America and is part of a collection in honor of Warren B. Hamilton.

Dissipating heat generated by internal radioactivity and leftover energy created when our planet formed are models for Earth's internal workings. The amount of internal heat-energy is not enough to drive large-scale tectonics. There are other problems with using convection to explain plate motions.

Earth's plates might be shifting because the sun exerts a strong pull on the moon that has caused it to become more elliptical.

The barycenter, the center of mass between the Earth and the moon, has moved closer to Earth's surface and is now 600 km away. As the Earth continues to spin, this sets up internal stresses.

The barycenter lies 4600 km from the center and Earth's pull and orbital acceleration are not balanced there. The planet's warm, thick and strong interior layers are not impervious to the stresses of the environment.

The Earth is flattened from a perfect spherical shape by daily spin. The authors suggest that the stresses created a mosaic of plates in the outer shell. The plate motions come from the changes in size and direction of the imbalanced forces with time.

How to test this alternative? One test would be a detailed examination of the tectonics of Pluto, which is too small and cold to convect, but has a giant moon and a surprisingly young surface.

The study shows that the presence and longevity of volcanism depends on a number of factors, including moon size, moon orientation, and rates of body spin and cooling.

Hofmeister noted that Earth is the only rocky planet with all the factors needed for plate tectonics.

She said that the moon and distance from the sun are essential.

The story was told

Washington University provides materials in St. Louis. The original was written by the author. Content can be edited for style and length.

Journal reference

Anne M. Hofmeister, Robert E. A new mechanism for plate tectonics links planetary energetics to moon size. The GSA Special Papers were published in 2022.