A meteorite impact larger than four Everests gave rise to life more than 3 billion years ago | Science

There was a time when the Earth was an easy target. Meteorites periodically fell on it, greatly changing its surface. 3.26 billion years ago, a giant space rock larger than four Mount Everests and 200 times larger than the one that wiped out the dinosaurs crashed into our planet and left a mark so monumental that scientists can trace it back to Earth. . Today. But he failed to put an end to life, which was beginning to awaken in the form of single-celled creatures. On the contrary, it strengthened it, according to a new study.

A study published this Monday in a scientific journal PNAS, describes some of the consequences that this meteorite, 30 to 60 kilometers in diameter and named S2, had on planetary dynamics. The lead author of the study is Nadia Drabon, an early Earth geologist at Harvard University in the US, who tracked the meteorite to the Barberton greenstone belt in South Africa. Drabon explains that “there are only a few places in the world that have such old stones. This is due to the fact that plate tectonics constantly destroys the earth’s crust. Barberton is one of those few places left and the rocks are remarkably well preserved.”

The first traces of exposure were found in the form of balls the size of a grain of sand. When such spectacular impacts occur, meteorites and parts of the Earth are vaporized. This cloud of rock vapor spreads throughout the world and spherical particles are formed. Researchers have found a similar layer associated with the impact that destroyed the dinosaurs, but it is less than a centimeter thick, while S2 is more than 15 centimeters thick.

The impact of this giant meteorite caused a tsunami that roiled the ocean and carried debris from the seabed to coastal areas. The heat from the collision led to the evaporation of the upper layer of the sea and, as a result, to a warming of the atmosphere. A thick cloud of dust covered everything, obscuring the planet and stopping any photosynthetic activity taking place.

In principle, the idea of ​​such a powerful meteorite impact could indicate that the entire Earth was devastated and life turned to ash. But it was actually an impulse, as Drabon points out: “Until recently, it was thought that the consequences would be catastrophic for evolution. However, this way of thinking is changing and it is now believed that life was not only resilient, but may even have benefited from such violent events.”

Fertilizer pump

The researchers’ analysis shows that bacterial life is quickly restored, leading to a sharp increase in populations of single-celled organisms. Even bacteria need to eat, and the meteorite provided the perfect recipe for them. It is likely, the article elaborates, that the tsunami caused by the impact dragged iron trapped in the deep ocean into shallow waters, and that both the space rock itself and increased soil erosion added phosphorus to the Earth’s surface.

Scientists have no doubt that the meteorite likely had an initial negative impact on any life forms that lived on land or in shallow waters. But after that first blow, life quickly recovered. Drabon details this: “Before impact, Earth’s early oceans were likely biological deserts due to a lack of nutrients and electron donors such as iron. “The accident resulted in the release of essential nutrients on a global scale.”

In fact, one of the students participating in the field research described the meteorite as a “fertilizer bomb.” According to the lead author of the study, it is emphasized that this violence would have had benefits for the life that was at the very beginning. “It allowed him to flourish,” Drabon says.

Juli Pereto, professor of biochemistry and molecular biology at the University of Valencia, notes that before the meteorite hit, ecosystems suffered from a shortage of these elements, which limited the spread of life. “After the impact, there was a kind of global fertilization that made the limiting chemical elements more available and gave rise to the diversification and spread of microorganisms,” says this researcher, who is not involved in the study.

Like the god Janus of Roman mythology, S2 had two faces. On the one hand, this could have catastrophic consequences for part of the nascent biosphere: those organisms that could not withstand temporary warming of the sea or darkening of the atmosphere, which could last for decades, perished. But it also represented an exceptional evolutionary opportunity for microorganisms whose distribution had previously been limited. “We can see this as further evidence of life’s extraordinary ability to adapt,” Pereto concludes.

This process, according to Jesús Martínez Frías, an expert on meteorites, planetary geology and astrobiology at CSIC and president of the Spanish Network of Planetology and Astrobiology, is similar to what happens during large volcanic eruptions. “They play a destructive role, affecting the environment and species, but also a constructive one, in that they restore the marine and continental context affected by the disaster,” he notes.

The just-published study opens a new line of research aimed at unraveling the mysteries of the early Earth. “We are studying how other microbes, such as those that metabolize sulfur, responded to the exposure,” Drabon said. His team is also analyzing environmental changes after other major events in our planet’s early history and how early living creatures took advantage of them.