A Giant Meteorite Ripped Up the Seafloor and Boiled Earth’s Oceans 3.26 Billion Years Ago. Then, Life Blossomed in Its Wake

Roughly 3.26 billion years ago, Earth had a “what doesn’t kill you makes you stronger” moment. A monster meteor dubbed “S2”—roughly the size of four Mount Everests and up to 200 times larger than the rock that decimated the dinosaurs—crashed into our planet. Now, however, a team of geologists suggests the cataclysm provided a surprising boost for early forms of life. Their findings were published in the journal Proceedings of the National Academy of Sciences on Monday.

“We think of impact events as being disastrous for life,” study co-author Nadja Drabon, a geologist at Harvard University, says in a statement. “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.”

Before the arrival of S2, Earth appeared very different from how it is today. Our planet was mostly covered in water, with a few volcanoes and islands rising above the vast ocean’s surface, Andrew Knoll, another co-author of the study and a geobiologist at Harvard University, tells Scientific American’s Douglas Fox. The oceans had very low levels of nutrients at the time, and both the oceans and the atmosphere contained almost no free oxygen.

This meant Earth likely sustained at least 98 percent less life than it does today, all of which would have been single-celled organisms called archaea. Then, S2 arrived.

“The effects of the impact would have been quick and ferocious,” Drabon tells Reuters’ Will Dunham. “The impactor hit with so much energy that it and whatever sediment or rock it hit vaporized. This rock vapor cloud and dust ejected from the crater would have circled the globe and turned the sky black within hours.”

S2 landed in the ocean, triggering a huge tsunami that tore up the seafloor and flooded the few existing coastlines. The heat from the impact caused the upper ocean to boil. However, these hellish events may have also delivered surprising benefits.

The geologists estimate that S2 delivered 363 billion metric tons of phosphorus, a biological nutrient essential to life, into the oceans. The tsunamis would have dragged in even more phosphorus from the land, as well as churned up iron, an important energy source for some microorganisms, from deep-sea layers.

“The impact released essential nutrients, such as phosphorus, on a global scale,” Drabon tells CNN’s Ashley Strickland. “A student aptly called this impact a ‘fertilizer bomb.’”

Researchers reconstructed this story of the ancient impact by studying rocks from a region of South Africa called the Barberton Greenstone Belt. They extracted samples of sediments deposited long ago on the coastal seafloor, both below and above the impact layer of S2—sites that chronologically correspond to before and after the event.

The oldest layers contained prehistoric organic carbon that represents the remains of microbes that once thrived on the seafloor. Above these sheets were thick layers of spherules—solidified droplets of molten rock that form after meteorite impacts—which rained down in the wake of several impact events at the time. The spherules were mixed with sand and pebbles kicked up by the resulting tsunamis. And on top of that were layers of petrified mud that slowly settled after the S2 impact, along with salt crystals left behind by the evaporating oceans.

But the samples from farther above the impact layer present some of the most interesting clues: Geologists found sheets of ancient microbes again—perhaps even more than before—mixed in with an iron mineral called siderite. Rocks in these younger layers also had high levels of phosphorus. This suggests that life not only recovered after the meteorite impact—it blossomed, thanks to the delivery of essential nutrients.

By studying carbon isotopes in both the older and younger layers of microbes, the geologists also noted a shift toward iron-dependent microorganisms in the oceans, per Scientific American. Though the shift was short-lived, it helps scientists understand what life may have looked like on Earth during this period, per the statement.

It is “impressive that despite the very local nature of these observations … we can start to understand something about the global nature of these giant impact events,” Benjamin P. Weiss, an Earth and planetary scientist at the Massachusetts Institute of Technology who wasn’t involved in the study, tells CNN.

Now, by studying other early meteorite strikes, Drabon and her team plan to deepen their study of how life on Earth was impacted—and perhaps even fueled—by meteors.

Margherita Bassi | READ MORE

Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.