What happened when the giant S2 meteor hit Earth 3 billion years ago? –Harvard Gazette

Billions of years ago, long before anything resembling life as we know it existed, meteorites frequently struck the planet. One such space rock crashed about 3.26 billion years ago and continues to reveal secrets about Earth’s past today.

Nadja Drabon, an early Earth geologist and assistant professor in the Department of Earth and Planetary Sciences, has questions about what our planet looked like in ancient eons marked by meteor bombardment, when only single-celled bacteria and archaea ruled—and when everything began to change. When did the first oceans appear? Continents? Plate tectonics? How did all these violent influences affect the development of life?

Their new study in Proceedings of the National Academy of Sciences attempts to answer some of these questions related to the inauspiciously named “S2” meteorite impact more than 3 billion years ago, for which geological evidence has been found in the Barberton-Greenstone Belt in South Africa. Through the painstaking work of collecting and studying rock samples at centimeters apart and analyzing the sedimentology, geochemistry and carbon isotope compositions they leave behind, Drabon’s team paints the most compelling picture yet of what happened that day as a meteorite the size of four Mount Everest’s impact Pay a visit to the earth.

“Imagine you are standing off the coast of Cape Cod, in a shallow body of water. It is a low energy environment without strong currents. Then suddenly a huge tsunami sweeps past and tears up the ocean floor,” Drabon said.

The S2 meteorite, estimated to be up to 200 times larger than the one that killed the dinosaurs, triggered a tsunami that churned the ocean and washed debris from land into coastal areas. The heat from the impact vaporized the top layer of the ocean while warming the atmosphere. A thick cloud of dust covered everything, stopping all photosynthetic activity.

But bacteria are resilient, and after the impact, bacterial life recovered quickly, according to the team’s analysis. This was accompanied by a sharp increase in the populations of single-celled organisms that feed on the elements phosphorus and iron. Iron was likely swept up from the deep sea into shallow waters by the aforementioned tsunami, and phosphorus was brought to Earth by the meteorite itself and by increasing weathering and erosion on land.

Drabon’s analysis shows that iron-metabolizing bacteria flourished immediately after the impact. This shift toward iron-promoting bacteria, however short-lived, is an important piece of the puzzle describing early life on Earth. According to Drabon’s study, meteor impacts—even though they supposedly killed everything in their path (including the dinosaurs 66 million years ago)—had a lifelong silver lining.

“But what this study highlights is that these effects would have had benefits for life, particularly in the early stages, and that these effects would have actually allowed life to thrive.”

Nadia Drabon

“We think impact events are catastrophic for life,” Drabon said. “But what this study highlights is that these impacts would have had benefits for life, particularly in the early stages, and that these impacts would actually have allowed life to thrive.”

These findings come from the pioneering work of geologists like Drabon and her students, who hiked into mountain passes that contained sedimentary evidence of early rocks that became embedded in the ground and preserved in the Earth’s crust over time. Chemical signatures hidden in thin layers of rock help Drabon and her students piece together evidence of tsunamis and other catastrophic events.

The Barberton Greenstone Belt in South Africa, where Drabon focuses most of her current work, contains evidence of at least eight impact events, including S2. She and her team plan to continue studying the area to delve even deeper into the Earth and its meteorite-caused history.