Recovery of Earth after the Moon-forming giant impact

The last event in the main stage of Earth’s accretion is thought to be the Moon-forming giant impact. Another planet-sized body collided with the proto-Earth injecting material into orbit out of which the Moon formed. The Moon-forming impact is likely the most energetic event the Earth ever experienced, and Earth was left rapidly rotating and with a mantle that was substantially melted and vaporized. The post-impact body was many times larger than the present-day Earth, substantially oblate, and more like a silicate gas-giant than the terrestrial planets we see in our solar system today. How Earth transitioned from this hot, rapidly rotating state to a temperate, slowly rotating planet is poorly understood. In this talk, I will describe how the internal pressures and energy budget of Earth evolved as the planet cooled and its rotation rate was slowed by the tidal recession of the Moon. I will show that the internal pressures in the aftermath of the impact could be as low as half that in the present-day Earth and increased over time with significant implications for how the mantle froze and the interpretation of geochemical tracers of core formation. I will also discuss how the changing shape of Earth during lunar tidal recession could have driven tectonics on early Earth, providing a previously unrecognized driver for production of felsic rocks in the first few tens of millions of years of Earth’s history.