233-1 Cosmic bombardments on early Earth

Session: Impact Cratering and the Evolution of Life

Presenting Author:

Author:

Abstract:

The earliest geochemical evidence for life approaches 4 billion years ago—just a few hundred million years after our planet’s formation—at a time when the Earth was rapidly evolving. As prebiotic chemical processes that ultimately led to life were emerging, the early Earth was subject to a tremendous cosmic bombardment that fundamentally altered its near-surface environments.

Advances have recently been made in understanding the nature and rate of collisions between the early Earth and planetesimals leftover of planetary accretion. A combination of geophysical observations, geochemical data, and dynamical models have been used to constrain the oldest (>3.8-3.9 Ga) terrestrial collisional history (e.g., Marchi et al. 2014; Morbidelli et al. 2018; Nesvorny et al. 2022). These models primarily rely on observational constraints such as lunar cratering rates inferred from crater counts and sample radiometric ages, as well as concentrations of highly siderophile elements in lunar and terrestrial rocks. The subsequent ~3.5-2.5 Ga impact flux has been constrained thanks to preserved records of terrestrial collisions, such as impact-generated spherule layers (Glass & Simonson 2013; Marchi et al. 2021). 

These impact models show that the early Earth was pummeled by hundreds of impactors larger than 100 km in diameter, and countless smaller ones. It is hard to overstate the effects of these impacts on the environment. Processes such as widespread crustal melting and hydrothermal circulations would have affected prebiotic evolution pathways and early life, just to give some examples. In this talk, I will review the present knowledge of the early Earth impact flux, and discuss some of the key environmental consequences.

Glass B. & Simonson B. 10.1007/978-3-540-88262-6, 2013.

Marchi S., et al. Nature 511, 578, 2014.

Marchi S., et al. Nature Geoscience 14, 827, 2021.

Morbidelli A., et al. Icarus 305, 262, 2018.

Nesvorsny et al. ApJL 941, 2022.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8167

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