(CN) — Billions of years ago, colossal space rocks — some even bigger than the one that wiped out the dinosaurs 66 million years ago — may have collided with Earth every 15 million years, according to new research.
The findings, to be presented at the Goldschmidt geochemistry conference this week, indicate that “current models of Earth's early bombardment severely underestimate the number of known impacts,” researcher Simone Marchi, of the Southwest Research Institute in Boulder, Colorado, said in a statement.
The true number of impacts, taking place between 3.5 and 2.5 billion years ago, could be up to 10 times higher than previously thought, Marchi said, and point to an emerging possibility that each large-scale collision had a significant effect on the Earth's ability to support life.
Scientists say it indicates the formation of early life must have taken place under the influence, and perhaps as a result of, effects caused by the collisions.
Echoes of those impacts are found in ancient rocks containing “spherules,” small spherical glassy particles formed after the huge impacts threw up molten particles and vapors which then turned into glass as they cooled and fell to Earth to be embedded in rock.
The greater the impact, the more these particles would have spread from the impact site, scientists note, so global distribution of a thick spherule layer shows a huge impact.
“This means that in that early period, we were probably being hit by a Chicxulub-sized impact on average every 15 million years,” Marchi said.
Chicxulub is the name of the 6-mile-wide asteroid that struck Earth 66 million years ago in what is now called the Yucatan Peninsula, creating a crater roughly twice the size of Paris.
In addition to earthquakes, volcano eruptions and tsunamis, that cataclysmic impact caused smoke, ash and debris to engulf the atmosphere, radically changing the climate and eventually destroying most plants and wiping out 75% of species on Earth.
But the early Earth was very different from the Earth at the time of the Chicxulub impact, scientists say, and so were the effects of its collisions.
“The early Earth could have collided with objects up to thousands of kilometers across,” Marchi said. “Each one of those events would have obliterated in a blink of an eye large portions of the Earth's surface, covered the whole surface with a thick pile of hot debris, and possibly have caused complete vaporization of the oceans. Quite a spectacle!”
Researchers are trying to understand if these cosmic collisions may have affected the evolution of atmospheric oxygen.
“We find that oxygen levels would have drastically fluctuated in the period of intense impacts,” Marchi said, as large collisions have the potential to remove oxygen from the atmosphere.
“This process would have been much more pronounced on the early Earth because of the lower concentration of atmospheric oxygen (so it is easier to remove it), and larger size of the impactors,” he said. “We are now starting to study how these atmospheric oxygen oscillations could have affected the evolution of early life — there is lots more to do!”
Researcher Rosalie Tostevin of the University of Cape Town, who was not involved in Marchi’s work, noted that Marchi’s findings are significant because scientists tend to focus on Earth’s levels of oxygen being controlled by the evolution of life.
“But bombardment with rocks from space provides an intriguing alternative,” Tostevin said in a statement.
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