© SwRIArtistโs depiction of asteroids impacting the early Earth.
A team led by Southwest Research Institute has updated its asteroid bombardment model of the Earth with the latest geologic evidence of ancient, large collisions. These models have been used to understand how impacts may have affected oxygen levels in the Earth's atmosphere in the Archean eon, 2.5 to 4 billion years ago.
When large asteroids or comets struck early Earth, the energy released melted and vaporized rocky materials in the Earth's crust. The small droplets of molten rock in the impact plume would condense, solidify and fall back to Earth, creating round, globally distributed sand-size particles. Known as impact spherules, these glassy particles populated multiple thin, discrete layers in the Earth's crust, ranging in age from about 2.4 to 3.5 billion years old. These Archean spherule layers are markers of ancient collisions. "In recent years, a number of new spherule layers have been identified in drill cores and outcrops,
increasing the total number of known impact events during the early Earth," said Dr. Nadja Drabon, a professor at Harvard University and a co-author of the paper.
"Current bombardment models underestimate the number of late Archean spherule layers, suggesting that the
impactor flux at that time was up to 10 times higher than previously thought," said SwRI's Dr. Simone Marchi, lead author of a paper about this research in
Nature Geoscience. "What's more, we find that the cumulative impactor mass delivered to the early Earth was an important 'sink' of oxygen, suggesting that early bombardment could have delayed oxidation of Earth's atmosphere."
The abundance of oxygen in Earth's atmosphere is due to a balance of production and removal processes. These new findings correspond to the geological record, which shows that oxygen levels in the atmosphere varied but stayed relatively low in the early Archean eon. Impacts by bodies larger than six miles (10 km) in diameter may have contributed to its scarcity, as limited oxygen present in the atmosphere of early Earth would have been chemically consumed by impact vapors, further reducing its abundance in the atmosphere.
Comment: It's a shame to see the research trend of 15-20 years ago veer off course away from comets as the likely cause of sudden catastrophic climate change. However, it's good to see that at least some climate science acknowledges that the only climate change worth really worrying about is the sudden, NATURALLY-CAUSED kind.
We get it though. Comets are just too much for people. It's scary to contemplate, and disturbs too many beliefs.