A giant meteorite caused the oceans to boil 3.2 billion years ago. Scientists say it was a ‘fertilizer bomb’ for life

(CNN) – A huge meteorite, roughly the size of four Mount Everests, crashed into Earth more than 3 billion years ago, and its impact may have been unexpectedly beneficial for early life on our planet, according to a new study.

Typically, when a large space rock hits Earth, the impacts are associated with catastrophic destruction, as was the case with the extinction of the dinosaurs 66 million years ago, when an asteroid about 10 kilometers wide crashed in front of Earth’s coast. Yucatan Peninsula, territory of modern Mexico.

But Earth was young and a very different place when the S2 meteorite, estimated to have a mass 50 to 200 times that of the Chicxulub asteroid that caused the extinction of the dinosaurs, collided with the planet 3.26 billion years ago. According to Nadia Drabon, assistant professor of earth and planetary sciences at Harvard University. She is also the lead author of a new study describing the impact of S2 and what followed, published Monday in the academic journal Proceedings of the National Academy of Sciences.

“Complex life had not yet formed, and only single-celled life existed in the form of bacteria and archaea,” Drabon wrote in an email. “It is likely that life once existed in the oceans, but not as much as today, partly due to lack of nutrients. Some even describe archaic oceans as “biological deserts.” The Archaic Eon was a water world in which several islands stood out. “It would have been an interesting sight since the oceans were likely green due to deep waters rich in iron.”

When the S2 meteorite struck, global chaos ensued, but the impact also removed ingredients that could have enriched bacterial life, Drabon said. The new findings could change scientists’ understanding of how Earth and its nascent life responded to the bombardment of space rocks shortly after the planet’s formation.

Early in Earth’s history, space rocks often collided with the young planet. The study’s authors estimate that “giant meteorites” larger than 10 km in diameter hit the planet at least every 15 million years, meaning that at least 16 giant meteorites collided with Earth during the Archaic Era. , lasting from 4000 to 2500 million years.

But the consequences of these impacts are not well known. And given the Earth’s ever-changing geology, with large craters covered in volcanic activity and the movement of tectonic plates, it is difficult to find evidence of what happened millions of years ago.

Drabon is one of the first Earth geologists to be intrigued by understanding what the planet was like before the first continents formed and how violent meteorite impacts influenced the evolution of life.

“These impacts must have significantly influenced the emergence and evolution of life on Earth. But exactly how remains a mystery,” Drabon said. “In my research, I wanted to look at real ‘shocking’ evidence of how giant impactors impacted early life.”

Drabon and his colleagues conducted field work looking for clues in the rocks of the Barberton Mahonjwa Mountains in South Africa. There, geological evidence of eight impacts that occurred between 3.6 and 3.2 billion years ago can be found in the rocks, traced through tiny particles of meteorite impacts called spherules.

These small round particles, which can be glassy or crystalline, are formed when large meteorites fall to Earth and form sedimentary layers in rocks known as spherical strata.

The team collected various samples in South Africa and analyzed the composition and geochemistry of the rocks.

“Our days usually start with a long hike through the mountains to get to the sampling sites,” Drabon said. “Sometimes we are lucky that dirt roads bring us closer. “On site, we examined the rock structures along the impact layer in great detail and used sledgehammers to extract samples for further analysis in the laboratory.”

The closely interlayered rock layers preserved a mineral chronology that allowed researchers to reconstruct what happened when the S2 meteorite struck.

At the time of its fall on the planet, the S2 meteorite had a diameter of 37 to 58 kilometers. The consequences were swift and brutal, Drabon said.

“Imagine you’re standing off the coast of Cape Cod, on a shallow shelf,” Drabon said. “It’s a low-energy environment with no strong currents. “And suddenly a gigantic tsunami appears, sweeping away and tearing up the seabed.”

The tsunami engulfed the entire planet, and the heat from the impact was so intense that the top layer of the ocean boiled. When oceans boil and evaporate, they form salts like those seen in rocks immediately after an impact, Drabon said.

The dust released into the atmosphere by the impact darkened the sky within hours, even on the opposite side of the planet. The atmosphere warmed, and a thick cloud of dust prevented microbes from converting sunlight into energy. Any form of life on land or in shallow waters would feel the adverse effects immediately, and these effects would last for years to decades.

Over time, rain would return to the upper layers of the ocean and the dust would settle.

But the deep ocean environment is a different story. The tsunami agitated elements such as iron and brought them to the surface. Meanwhile, erosion helped wash coastal debris out to sea and release phosphorus from the meteorite. Laboratory tests showed an increase in the presence of single-celled organisms that feed on iron and phosphorus immediately after the impact.

Life quickly recovered and then flourished, Drabon said.

“Before the impact, there was some life in the oceans, but little due to the lack of nutrients and electron donors, such as iron, in shallow waters,” he explained. “The impact released important nutrients such as phosphorus on a global scale. One student aptly called this effect a “fertilizer bomb.” “Overall, this is very good news for the evolution of early life on Earth, since in the early stages of life’s evolution impacts would have been much more frequent than they are today.”

The S2 and Chicxulub asteroid impacts had different impacts due to the respective sizes of the space rocks and the phase the planet was in when each struck, Drabon said.

The Chicxulub asteroid crashed into a carbonate shelf on Earth, releasing sulfur into the atmosphere. The emissions produced aerosols that caused a sharp and severe drop in surface temperature.

And while both impacts caused significant loss of life, resilient, sunlight-dependent microorganisms in shallow waters would quickly recover from the S2 impact once the oceans filled with water and the dust settled, Drabon said. “Life was much simpler during the S2 impact,” he said. “Think about brushing your teeth in the morning: you may kill 99.9% of the bacteria, but by the evening it will come back.”

Ben Weiss, the Robert R. Schrock Professor of Earth and Planetary Sciences at MIT, was intrigued by the paper’s geological observations of spherule layers, which he believes allow researchers to study ancient records of Earth’s collisions with the same objects. a way in which astronomers can study the surfaces of planets such as Mars. Weiss was not involved in the study.

“There are no surviving impact craters on Earth today that are close in size to those believed to have formed the rocks studied here,” Weiss said. “Of course, the thing about our data is that, fragmentary and incomplete as it may be, these are the only records that we can currently study in detail that can tell us about the impact of impacts on the early evolution of life. “What’s also exciting is that despite the very local nature of these observations (outcrops in a small region of South Africa), we can begin to understand something about the global nature of these giant impacts.”

Rocks from the Barberton-Makhonjwa Mountains open up a whole new direction for Drabon and his colleagues to study the history of collisions of space rocks with Earth.

“We are seeking to determine how widespread these environmental changes and biological responses were following other impacts in Earth’s early history,” he said. “Because the effect of each exposure depends on several factors, we want to assess the frequency with which these positive and negative life effects occurred.”