Cataclysm no more: New views on the timing and delivery of lunar impactors

TL;DR

This paper reviews lunar impact records and presents new interpretations, suggesting a prolonged bombardment period from 4.2 to 3.4 billion years ago rather than a sudden cataclysm at 3.9 billion years ago, affecting early Earth conditions.

Contribution

It offers a comprehensive review and new insights indicating a prolonged lunar impact period, challenging the traditional lunar cataclysm hypothesis.

Findings

Most evidence supports a prolonged bombardment from 4.2 to 3.4 Ga.

The lunar impact record does not show a spike at 3.9 Ga.

Implications for early life conditions are discussed.

Abstract

If properly interpreted, the impact record of the Moon, Earth's nearest neighbour, can be used to gain insights into how the Earth has been influenced by impacting events since its formation ~4.5 billion years (Ga) ago. However, the nature and timing of the lunar impactors - and indeed the lunar impact record itself - are not well understood. Of particular interest are the ages of lunar impact basins and what they tell us about the proposed "lunar cataclysm" and/or the late heavy bombardment (LHB), and how this impact episode may have affected early life on Earth or other planets. Investigations of the lunar impactor population over time have been undertaken and include analyses of orbital data and images; lunar, terrestrial, and other planetary sample data; and dynamical modelling. Here, the existing information regarding the nature of the lunar impact record is reviewed and new interpretations are presented. Importantly, it is demonstrated that most evidence supports a prolonged lunar (and thus, terrestrial) bombardment from ~4.2 to 3.4 Ga and not a cataclysmic spike at ~3.9 Ga. Implications for the conditions required for the origin of life are addressed.