Ancient Mega-Asteroid May Have Helped Life on Earth Flourish

Traditionally, giant space rocks colliding with Earth are seen as a bad thing for life. That’s certainly true now, but the primordial Earth of 3 billion years ago was a different place. A team from Harvard University studying an ancient impact known as S2 has discovered evidence the event may have given life a leg up. After the firestorms ended and clouds of dust settled, life on Earth may have been in a better place.

While a large asteroid could encounter Earth at any time, impacts were much more common in the so-called Archean Eon. Between 4 billion and 2.5 billion years ago, the only life on Earth consisted of simple single-celled organisms growing in shallow water. Harvard geologist Nadja Drabon studies this early phase of our planet and recently published a study analyzing the effects of S2, which was around four times the size of Mount Everest and 200 times larger than the Chixulub object that all but wiped out the dinosaurs.

Erosion and tectonic movement erased many details of S2’s impact about 3.26 billion years ago. It was a painstaking process of exploring the terrain centimeter by centimeter in the Barberton Greenstone belt of South Africa. Still, the team led by Dragbon was able to reconstruct the sequence of events during the S2 impact.

The immediate aftermath of the impact would have included all the bad you’d expect from a huge asteroid impact. After striking the ocean, the impactor produced an enormous tsunami. The heat from the impact vaporized the top layer of ocean water, leading to torrential storms. And then there was the dust, which would have halted photosynthesis on a global scale for months or years.

Interestingly, Drabon’s analysis reveals that the impact most likely churned up the ocean in a way that would have benefitted some early forms of life. Organisms that relied on light were out of luck, but the team’s analysis showed a substantial uptick in the prevalence of organisms that feed on phosphorus and iron. The study concludes that iron-rich water from the deep oceans was mixed into the shallows where life was beginning to take hold, helped by the tsunami to get much farther inland than it otherwise would have.

“We think of impact events as being disastrous for life,” Drabon said. “But what this study is highlighting is that these impacts would have had benefits to life, especially early on, and these impacts might have actually allowed life to flourish.”

Naturally, iron-eating bacteria did not remain the dominant form of life on Earth, but its short-lived prevalence could be a key part of Earth’s early history. Today, iron is still an essential element for life, and it’s possible its early redistribution by events like the S2 impact made Earth more hospitable. Drabon isn’t done with this line of inquiry—Barberton Greenstone contains evidence of at least eight Archaeozoic impacts that could support the conclusions in this study. Drabon hopes to continue the work soon.