It turns out that these giant meteorites actually had a positive effect on life compared to the later extinction-causing meteorites
Billions of years ago, long before life as we know it existed, meteorites hit the Earth with high frequency. One of those celestial bodies collided with Earth about 3.26 billion years ago, and to this day it reveals secrets about our planet's past.
Nadia Drabon, a geologist who studies the ancient Earth and an associate professor in the Department of Earth and Planetary Sciences at Harvard University, studies with great interest the era of meteorite bombs in ancient periods of the Earth, only bacteria and archaea allowed life. It focuses on questions such as when did the first oceans appear? How were the continents formed? And how did the violent injuries affect the development of life?
New research published in the journal Proceedings of the National Academy of Sciences Provides answers to some of these questions, particularly regarding the impact of the meteorite known as S2 which occurred more than 3 billion years ago, and whose impact is still preserved today in the rocks of the Greenstone Belt in Barberton, South Africa. Through the painstaking work of collecting and analyzing rock samples in centimeter intervals and examining the sedimentology, geochemistry and isotopic composition of the remaining carbon, Drabon's team paints a fascinating picture of what happened the day a meteorite the size of four Mount Everest hit Earth.
"Try to imagine yourself standing off the coast of Cape Cod, in an area of shallow water with no strong currents. Then suddenly, a huge tsunami comes and shakes the sea floor," said Drabon.
The S2 meteorite, estimated to be up to 200 times the size of the meteorite that wiped out the dinosaurs, caused a tsunami that stirred the ocean and transported fragments from the land to the coastal areas. The heat from the impact caused the upper layer of the ocean to boil, and the atmosphere warmed. A thick cloud of dust covered everything and stopped all photosynthetic activity.
However, bacteria are resilient, and according to the team's analysis, bacterial life recovered quickly after the impact. At the same time, there was a sharp increase in the populations of single-celled organisms that feed on phosphorus and iron. The iron, apparently, was brought up from the depths of the ocean to the shallow waters by the tsunami, and the phosphorus was supplied by the meteorite itself and by increased weathering and drifting processes on land.
Drabon's analysis shows that the bacteria that feed on iron thrived on the impact. This shift to iron-preferring bacteria, even if it was short-lived, is a key piece of the puzzle that describes early life on Earth. According to Drabon's research, meteorite impact events - which are known to be fatal - also carried benefits for life.
"We think of traumatic events as life-catastrophic," Drabon said. "But this study shows that these vulnerabilities had benefits for life, especially in the early stages ... These vulnerabilities may have actually allowed life to thrive."
These results stem from the painstaking fieldwork of geologists like Drabon and her students, who travel through mountain passes that contain the sedimentary evidence of ancient impacts. Chemical signatures hidden in thin layers of rock help Drabon and her team piece together the evidence for tsunamis and other catastrophic events.
The greenstone belt in Barberton, South Africa, where Drabon is focusing much of her current work, contains evidence of at least eight impact events, including S2. She and her team plan to continue to delve deeper into Earth's meteoric history.
