Around 3.26 billion years ago, an enormous meteorite slammed into Earth and surprisingly created conditions for some early lifeforms to flourish.
Evidence of these lucky lifeforms was discovered and described by early-Earth geologists publishing in the prestigious Proceedings of the National Academy of Sciences.
The meteorite, inconspicuously named “S2”, was up to 200 times larger than the meteorite that killed off most dinosaurs 66 million years ago.
S2 struck our planet early on, in the middle of the Archean Eon, which is the second eon of four in Earth’s geological history.
Meteorite strikes were common during the Archean. The geologists’ study site at the Barberton Greenstone Belt in South Africa records at least eight impact events, including S2.
Meanwhile, life on Earth had just begun but it only consisted of single-celled bacteria and archaea (evolutionarily distinct microorganisms about the size of bacteria).
The geology team, led by Nadja Drabon, an assistant professor at Harvard University, asked, ‘How did all those violent impacts affect the evolution of life?’
They reconstructed what happened the day S2 arrived and immediately afterwards, through comparisons of rock samples from the impact site and by characterising the sediments, chemicals and carbon isotopes of rocks sprayed by the collision.
“Picture yourself standing off the coast of Cape Cod, in a shelf of shallow water. It’s a low-energy environment, without strong currents. Then all of a sudden, you have a giant tsunami, sweeping by and ripping up the sea floor,” says Drabon.
Like the dinosaur-ending meteorite, a thick cloud of dust would have shut down photosynthesis and organisms which relied on it for energy.
But the team found that life rebounded quickly and that S2 had a silver lining – through the higher levels of iron and phosphorus.
Iron-metabolising bacteria flourished after the impact, likely because the tsunamis carried iron from the deep ocean to shallower waters. Similarly, phosphorus-metabolising bacteria increased because the meteorite contained this element.
“We think of impact events as being disastrous for life,” says Drabon. “But what this study is highlighting is that these impacts would have had benefits to life, especially early on… these impacts might have actually allowed life to flourish.”
