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

() – A huge meteorite, the estimated size of four Mount Everests, crashed into Earth more than 3 billion years ago, and the impact could have been unexpectedly beneficial to early life on our planet, according to new research.

Typically, when a large space rock hits Earth, the impacts are associated with catastrophic devastation, as in the case of the demise of the dinosaurs 66 million years ago, when an asteroid about 10 kilometers wide crashed in front of the Earth. the coast of the Yucatan Peninsula, in what is now Mexico.

But the Earth was young and a very different place when the S2 meteorite, whose mass is estimated to be between 50 and 200 times greater than that of the Chicxulub asteroid, which triggered the extinction of the dinosaurs, collided with the planet 3.26 billion years ago, according to Nadja Drabon, associate professor of Earth and Planetary Sciences at Harvard University. She is also the main author of a new study describing the impact of S2 and what followed after it, published Monday in the academic journal Proceedings of the National Academy of Sciences.

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

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

Early in Earth’s history, space rocks frequently collided with the young planet. According to the study’s authors, the “giant impactors,” more than 10 km in diameter, are estimated to have hit the planet at least every 15 million years, meaning that at least 16 giant meteorites collided with Earth during the Eon. archaic, which lasted from 4,000 to 2,500 million years.

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

Drabon is an early Earth geologist intrigued by understanding what the planet was like before the first continents formed and how violent meteorite impacts affected the evolution of life.

“These impacts must have significantly affected the origin and evolution of life on Earth. But how exactly remains a mystery,” Drabon said. “In my research, I wanted to examine actual ‘shock’ evidence of how giant impactors affected early life.”

Drabon and his colleagues conducted field work to search for clues in the rocks of South Africa’s Barberton Makhonjwa Mountains. There, geological evidence of eight impacts, occurring between 3.6 and 3.2 billion years ago, can be found in the rocks, traced through tiny meteorite impact particles called spherules.

These small round particles, which can be glassy or crystalline, are produced when large meteorites impact the Earth, and form sedimentary layers in rocks known as spherule beds.

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 our sampling sites,” Drabon said. “Sometimes we are lucky to have dirt roads that bring us closer. “At the site, we studied the rock structures along the impact event layer in great detail and used sledgehammers to extract samples for further analysis in the laboratory.”

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

The S2 meteorite was between 37 and 58 kilometers in diameter when it hit the planet. The effects were quick and ferocious, Drabon said.

“Imagine standing off the coast of Cape Cod, on a shelf of shallow water,” Drabon said. “It is a low energy environment, without strong currents. “Then suddenly you have a giant tsunami, sweeping and tearing up the seabed.”

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

Dust injected into the atmosphere by the impact darkened the skies within hours, even on the opposite side of the planet. The atmosphere warmed and the thick dust cloud prevented microbes from converting sunlight into energy. Any life form on land or in shallow water would have felt the adverse effects immediately, and those effects would have persisted from a few years to decades.

Over time, the rain would have returned the upper layers of the ocean and the dust would have settled.

But the deep ocean environment was another story. The tsunami stirred up elements like iron and brought them to the surface. Meanwhile, erosion helped wash coastal debris into the sea and released phosphorus from the meteorite. Laboratory analyzes 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 prospered, Drabon said.

“Before the impact, there was some life in the oceans, but not much, due to the lack of nutrients and electron donors, such as iron, in the shallow waters,” he explained. “The impact released essential nutrients, such as phosphorus, on a global scale. One student aptly called this impact ‘fertilizer bomb’. “Overall, this is very good news for the evolution of early life on Earth, as impacts would have been much more frequent during the early stages of life evolution than today.”

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

The Chicxulub asteroid hit a carbonate shelf on Earth, releasing sulfur into the atmosphere. The emissions formed aerosols that caused a sharp and extreme drop in surface temperatures.

And although both impacts caused significant die-offs, the resilient, sunlight-dependent microorganisms in shallow waters would have recovered quickly after the S2 impact once the oceans refilled and the dust settled, Drabon said. “Life at the time of the S2 impact was much simpler,” he said. “Think about brushing your teeth in the morning: you may eliminate 99.9% of the bacteria, but by evening they are back.”

Ben Weiss, Robert R. Shrock Professor of Earth and Planetary Sciences at the Massachusetts Institute of Technology, was intrigued by the geological observations of the spherule beds in the paper, which he believes are allowing researchers to explore Earth’s ancient record of impacts in the same way that astronomers can study the surfaces of planets like Mars. Weiss was not involved in the study.

“There are no preserved impact craters on Earth today that come close in size to those that have been inferred to have produced the rocks studied here,” Weiss said. “Of course, what is special about our record is that, however fragmentary and incomplete, it is the only record that we can currently study in detail and that can tell us about the effects of impacts on the early evolution of life. “It is also impressive 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 gigantic impacts.”

The rocks from the Barberton Makhonjwa Mountains are opening up a whole new line of research for Drabon and his colleagues into the history of space rock impacts on Earth.

“We aim to determine how common these environmental changes and biological responses were after other impacts in Earth’s early history,” he said. “As the effect of each impact depends on several factors, we want to evaluate the frequency with which these positive and negative effects on life occurred.”