Giant meteorite impact 3.26 billion years ago may have contributed to the start of life

Billions of years ago, long before anything resembling life as we know it existed, meteorites frequently struck the planet. One of these space rocks crashed about 3.26 billion years ago, and even today it reveals secrets about Earth’s past.

Nadja Drabon, an early Earth geologist and assistant professor in the Department of Earth and Planetary Sciences, is insatiably curious about what our planet looked like during ancient eons of meteor bombardment, when only single-celled bacteria and the archaea ruled – and when she did everything began to change. When did the first oceans appear? And the continents? Plate tectonics? How have all these violent impacts affected the evolution of life?

A study in Proceedings of the National Academy of Sciences sheds light on some of these questions, in relation to the accidentally named “S2” meteor impact that occurred more than 3 billion years ago, and for which geological evidence is found today in the Greenstone Belt of Barberton in South Africa.

Through painstaking work collecting and examining rock samples spaced just centimeters apart and analyzing the sedimentology, geochemistry, and carbon isotopic compositions they leave behind, Drabon’s team maps the most compelling picture yet of what happened the day a meteorite the size of four Mount Everests paid off. Land a visit.

“Imagine yourself off the coast of Cape Cod, in a shallow body of water. It’s a low-energy environment, with no strong currents. Then all of a sudden you have a giant tsunami, sweeping up and tearing up the bottom marine.” » said Drabon.

The S2 meteorite, estimated to be up to 200 times larger than the one that killed the dinosaurs, triggered a tsunami that mixed the ocean and carried debris from land to coastal areas. The heat released by the impact caused the upper layer of the ocean to boil, while warming the atmosphere. A thick cloud of dust covered everything, interrupting all photosynthetic activity.

But bacteria are hardy, and after the impact, according to the team’s analysis, bacterial life quickly rebounded. This was accompanied by a sharp increase in populations of single-celled organisms that feed on the elements phosphorus and iron.

The iron was likely transported from the depths of the ocean to shallow waters by the aforementioned tsunami, and the phosphorus was brought to Earth by the meteorite itself and by increased weathering and land erosion .

Drabon’s analysis shows that iron-metabolizing bacteria would therefore have thrived immediately after the impact. This evolution towards iron-friendly bacteria, even if short-lived, is a key piece of the puzzle illustrating the beginnings of life on Earth. According to Drabon’s study, meteorite impacts, although known to kill anything in their wake (including, 66 million years ago, dinosaurs), had a positive side for life.

“We think impact events are disastrous for life,” Drabon said. “But what this study highlights is that these impacts would have had beneficial effects on life, especially early on…these impacts could actually have allowed life to flourish.”

These results came from the backbreaking work of geologists like Drabon and his students, who traveled over mountain passes that contain sedimentary evidence of the first sheaves of rocks that sank into the ground and were preserved over time in the earth’s crust. Chemical signatures hidden in thin layers of rock help Drabon and his students piece together evidence of tsunamis and other cataclysmic events.

The Barberton greenstone belt in South Africa, where Drabon focuses most of his current work, contains evidence of at least eight impact events, including S2. She and her team plan to study the region further to probe even deeper into Earth and its meteorite-related history.