Bigger than the dinosaur-killer, asteroid S2 smashed life on Earth into a higher gear

Research published in the Proceedings of the National Academy of Sciences revealed that a colossal asteroid impact over 3.26 billion years ago may have provided a crucial boost to Earth's early biosphere. The study suggests that the impact, from a meteorite known as "S2," acted like a "giant fertilizer bomb," enriching the environment with essential nutrients and allowing primitive life forms to flourish.

Dr. Nadja Drabon, an assistant professor of Earth and Planetary Sciences at Harvard University, led the team investigating the consequences of the S2 meteorite impact. "We think of impacts as having catastrophic consequences for life," Drabon said. "But this study shows that these impacts also had advantages for life, especially in the early times. These impacts could have actually made life flourish."

BBC, Newsweek, O Globo, and Der Spiegel were among the news sites that reported on the discovery.

The S2 meteorite, estimated to be between 37 and 58 kilometers in diameter—200 times larger than the asteroid that contributed to the extinction of the dinosaurs—collided with Earth during the Paleoarchean Era. At that time, the planet was predominantly a water world with limited land masses, and life was in its earliest stages, composed mainly of unicellular microorganisms like bacteria and archaea.

The impact was immensely powerful, creating a crater approximately 500 kilometers wide and ejecting at least 10,000 cubic kilometers of vaporized rock into the atmosphere. "The tsunami swept across the Earth, and the heat from the impact was so intense that it boiled the upper layer of the ocean," Drabon noted. The immediate effects included a dense cloud of dust enveloping the planet, blocking sunlight, and halting photosynthetic activity. Despite these catastrophic conditions, life not only recovered but thrived in the aftermath.

Researchers found that the violent disturbances stirred up nutrients such as phosphorus and iron, enriching the environment for early life forms. These nutrients likely reached the ocean through the churning of the sea floor by massive tsunamis and from the erosion of land caused by seismic activities following the impact. "It's like when you brush your teeth in the morning. You kill 99.9% of the bacteria, but by night, they're all back," Drabon explained, highlighting the resilience and rapid reproduction of simple microorganisms.

Fieldwork was conducted in South Africa's Barberton Greenstone Belt, one of the oldest geological formations on Earth, containing rocks up to 3.6 billion years old and evidence of at least eight ancient impacts. Drabon and her team collected and analyzed rock samples, examining their geochemistry, sedimentology, and carbon isotope compositions. They searched for spherules—tiny particles formed from vaporized rock—to trace the layers corresponding to the time of the impact.

The analyses revealed significant changes in the rock formations above the impact layer, including increased amounts of nutrients and iron. These conditions created an environment conducive to a bloom of microbial life. "Life during the time of the S2 impact was much simpler," Drabon said. "It seems that life after the impact found really favorable conditions that allowed it to flourish."

The study suggests that the influx of nutrients acted as a catalyst for the rapid recovery and expansion of unicellular organisms. Populations that metabolized iron and phosphorus experienced strong increases, indicating an evolutionary opportunity spurred by the impact. This resilience contrasts with later events like the Chicxulub impact, which contributed to the mass extinction of the dinosaurs and many other life forms due to the more complex ecosystems and organisms present at that time.

The implications of these findings extend beyond understanding Earth's ancient past. They offer insights into the potential resilience and adaptability of microbial life in extreme conditions, which could inform the search for life elsewhere in the universe. Drabon and her colleagues aim to further investigate how common such environmental changes and biological responses were after other impacts in Earth's early history. "Since the effect of each impact depends on various factors, we want to assess how frequently such positive and negative effects on life occurred," she said.

This research provides a nuanced perspective on the role of asteroid impacts in the evolution of life on Earth. Rather than solely agents of destruction, these colossal events may have also created opportunities for life to emerge and thrive. As Drabon concluded, "Our work suggests that, on a global scale, early life may have benefited from an influx of nutrients and electron donors, as well as new environments, as a result of major impact events."

This article was written in collaboration with generative AI company Alchemiq