4.5 billion years ago, a planet collided with ours and gave us the Moon. And maybe something else

A new explanation for the existence of plate tectonics and seismic movements based on this influence

The history of our planet as we know it may have begun with the collision of two early planets in our solar system, Gaia and Theia. It’s because of this influence that we have the Moon, and we might also have this influence because of another fundamental characteristic of our Earth: plate tectonics.

Shock and movement. Using geodynamic models, a team of researchers from the California Institute of Technology (CalTech) concluded that the collision between Gaia and Theia, which gave rise to the modern Earth and Moon, was crucial for our planet to have some dynamic tectonic plates in its day.

“Flooded Continents”The study is based on the so-called Large Low Velocity Provinces (LLVP). These are two large masses of rock located at the bottom of the Earth’s mantle, discovered in the 1980s.

These masses have geochemical characteristics that distinguish them from the rest of the Earth’s mantle. It is to this fact that they owe their name, since seismic waves when passing through them slow down compared to the rest of the mantle.

A study published a few months ago suggested that these large masses were possible remnants of Gaia, a planet that collided with the “proto-Earth” (Theia or Theia). Some of the matter released after the impact would eventually coalesce gravitationally to form the Moon. The remnants of Gaia, in turn, would eventually be “absorbed” within the Earth.

Geodynamics. The new study builds on this hypothesis. The team started with this event when formulating their geodynamic models and simulating what happened. The team used the information we have about the composition of LLVPs to also understand how they influence thermal circulation in the Earth’s mantle.

They concluded that by cracking the planet’s surface, the impact could lead to a sequence of subduction movements between different plates that “float” in the Earth’s mantle.

Zirconium crystal. The team notes that this hypothesis could explain the oldest mineral on Earth—zirconium crystals. As they explain, these formations could have been formed as a result of subduction movements more than 4 billion years ago.

Details of the study were recently published in a journal article. Letters on Geophysical Research.

Science has not yet been created. The fact that this work was formulated on the basis of a hypothesis that has yet to be proven limits our ability to reach a conclusion on this issue.

Getting into the first hundreds of millions of years of our planet’s existence is extremely difficult. Geological data in these cases are very limited. If you exclude meteorites—rocks that did not form on our planet—the oldest samples we have are about 4 billion years old.

This is one of the reasons why samples recovered from beyond Earth, such as those from Bennu or the lunar regolith we bring back from our satellite, are so important. Even if we want to understand our planet.

In Hatak | The moon is 40 million years older than we thought. We know this thanks to some old samples

Image | Modeling the consequences of exposure. NASA Ames Research Center