Giant meteorite impacts likely greatly impacted the early Earth’s ability to support life. During the Archean Eon, scientists have found evidence of at least 16 significant impacts from large objects over 10 kilometers wide. These impacts probably caused serious but short-term changes to the surface environment. However, we don’t fully understand how these events affected early life on Earth.
One such space rock 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, with her team, analyzed the sedimentology, petrography, and carbon isotope geochemistry of sedimentary rocks across the S2 impact event (37 to 58 km carbonaceous chondrite) forming part of the 3.26 Ga Fig Tree Group, South Africa, to evaluate its environmental effects and biological consequences.
By carefully collecting and studying rock samples just centimeters apart and analyzing the sediment, chemistry, and carbon isotopes, Drabon’s team has created the clearest picture yet of what happened when a meteorite the size of four Mount Everests struck Earth.
Drabon said, “Picture yourself standing off the coast of Cape Cod, in a shelf of shallow water. It’s a low-energy environment without strong currents. Then, all of a sudden, you have a giant tsunami sweeping by and ripping up the sea floor.”
The S2 meteorite, much larger than the one that killed the dinosaurs, caused a massive tsunami that mixed the ocean and swept debris into coastal areas. The impact generated intense heat, boiling the top layer of the ocean and warming the atmosphere, while a thick dust cloud blocked sunlight and halted photosynthesis.
Despite these harsh conditions, bacteria proved resilient. Following the impact, their populations quickly rebounded particularly unicellular organisms that thrived on phosphorus and iron. The tsunami likely stirred up iron from the deep ocean, while phosphorus came from the meteorite and increased weathering on land.
Drabon’s analysis reveals that iron-metabolizing bacteria thrived in the immediate aftermath of the impact. This temporary rise in iron-loving bacteria provides essential insights into early life on Earth.
According to Drabon’s study, while meteorite impacts are often thought to wipe out life—like the event that killed the dinosaurs 66 million years ago—they also had a surprising benefit for some life forms.
Drabon said, “We think of impact events as disastrous for life. But this study highlights that these impacts would have had benefits to life, especially early on, and these impacts might have allowed life to flourish.”
These findings come from the hard work of geologists like Drabon and her students, who hike into mountain passes to study sedimentary layers that preserve ancient rock debris. Examining chemical signatures in these thin layers can uncover evidence of tsunamis and other significant events in Earth’s history.
Drabon focuses much of her research on the Barberton Greenstone Belt in South Africa, which shows signs of at least eight impact events, including the S2 meteorite. She and her team plan to continue their studies to explore more about Earth’s history and the role of meteorite impacts.
Journal Reference:
- Nadja Drabon, Andrew Knoll, Donald Lowe, et al. Effect of a giant meteorite impact on Paleoarchean surface environments and life. PNAS. DOI: 10.1073/pnas.2408721121
