Earth's Earliest Evolution: Fire From Above, Fire From Below
When
Where
Dr. Simone Marchi
Senior Research Scientist
Southwest Research Institute
In the aftermath of the giant collision resulting in the formation of the Moon, about 4.5 billion years ago, the Earth experienced a protracted time of bombardment by leftover planetesimals. In this talk I will present a new bombardment model of the Hadean Earth that has been calibrated using existing lunar and terrestrial geochemical data. We find that the surface of the Hadean Earth was widely reprocessed by impacts through mixing and burial by impact-generated melt. This model may explain the absence of early terrestrial rocks. In addition, by tracking the magnitude and timing of large collisions, we find that existing oceans would have repeatedly boiled away into steam atmospheres as late as about 4 billion years ago. These findings have important implications for the formation and stability of early habitable environments and the onset of life. Finally, I will discuss recent developments in understanding the effects of collisions on the tectonic evolution of the early Earth, as well as the formation of impact-induced geochemical heterogeneities that could still persist in terrestrial mantle rocks.