Delayed and variable late Archaean atmospheric oxidation due to high collision rates on Earth
S. Marchi, N. Drabon, T. Schulz, L. Schaefer, D. Nesvorny, W. F. Bottke, C. Koeberl & T. Lyons
Nature Geoscience
Published: 21 October 2021
“Frequent violent collisions of impactors from space punctuated the geological and atmospheric evolution of early Earth. It is generally accepted that the most massive collisions altered the chemistry of Earth’s earliest atmosphere, but the consequences of Archaean collisions for atmospheric oxidation are little understood. Early Archaean (4.0–3.5 billion years ago (Ga)) impact flux models are tightly constrained by lunar cratering and radiometric data. Further, a record of the late Archaean (3.5–2.5 Ga) impact flux is provided by terrestrial impact spherule layers—formed by collisions with bodies ≥10–20 km in diameter—although this record is probably incomplete and significant uncertainties remain. Here we show, on the basis of an assessment of impactor-related spherule records and modelling of the atmospheric effects of these impacts, that current bombardment models underestimate the number of late Archaean spherule layers. These findings suggest that the late Archaean impactor flux was up to a factor of ten higher than previously thought. We find that the delivered impactor mass was an important sink of oxygen, suggesting that early bombardment could have delayed Earth’s atmosphere oxidation. In addition, late Archaean large impacts (≥10 km) probably caused drastic oscillations of atmospheric oxygen, with an average time between consecutive collisions of about 15 Myr. This pattern is consistent with a known episode of atmospheric oxygen oscillation at ~2.5 Ga that is bracketed by large impacts recorded by Bee Gorge (~2.54 Ga) and Dales Gorge (~2.49 Ga) spherule layers.”
