Earth’s early years were unimaginably violent compared to what we have today.
The evolution after the complete formation of our planet was plagued by complex geophysical processes that, in addition, were greatly affected by interplanetary collisions over hundreds of millions of years. Now, new research suggests that the number of collisions the early Earth suffered may have been 10 times greater than previously thought. And each impact would have been significantly larger than the asteroid that killed the dinosaurs 65 million years ago, believed to be seven miles wide. Some of these individual impacts could have been the size of a city or even the size of a small province.
The asteroids that struck our planet between 2.5 and 3.5 billion years ago would have occurred with an impact frequency of “only” 15 million years and this would have had a significant effect on the chemistry near the Earth’s surface and on the ability to sustain life.
While the craters formed by these ancient collisions have worn away or destroyed over time, their traces can still be identified in forms of glassy particles called spherules. These spherules were formed as a result of impacts that spewed molten particles and vapors into the atmosphere, where they cooled and fell back to Earth. Their distribution can also reveal information about the size of the asteroid: the larger the colliding body, the further away the spherules are deposited.
“We have developed a new impact flow model and compared it with a statistical analysis of data from layers of old spherules. Using this approach, we found that current models of Earth’s early bombardment severely underestimate the number of known impacts, as recorded by the spherule layers. The true impact flux could have been up to a factor 10 times greater than previously thought in the period 3.5 to 2.5 billion years ago. This means that in that early period, we were probably being hit by an impact the size of Chicxulub on average every 15 million years. Quite a sight! “Explains Simone Marchi of the Southwest Research Institute (Boulder, CO, USA).
It seems that as we progress in our understanding of the old Earth we discover that what seemed to make sense then has turned out to be a far more impetuous and violent scenario.
“They are often neglected because we lack detailed knowledge of their number and magnitude, but it is likely that these energetic events have fundamentally altered the evolution of the Earth’s surface and atmosphere. For example, one result we are seeing is trying to understand whether these impacts may have affected the evolution of atmospheric oxygen. We found that oxygen levels would have fluctuated dramatically in the period of intense impacts. Given the importance of oxygen for the development of the Earth, and indeed for the development of life, its possible connection to collisions is intriguing and warrants further investigation. This is the next stage of our work ”, clarifies Marchi.
The full results of the study were presented at the 2021 Goldschmidt Conference, which took place July 4-9 and is organized by the European Association of Geochemistry and the Geochemical Society.
Referencia: Simone Marchi. Earth’s wild years. Goldschmidt 2021, paper # 8158
