WASHINGTON (Reuters) – Scientists have identified the oldest impact crater on Earth, and in doing so, they may have solved a mystery about how our planet emerged from one of its most terrible periods.
ARCHIVE PHOTO: An illustration shows glaciers covering the planet in ice in the so-called "snowball on Earth" period billions of years ago. NASA / Disclosure via REUTERS
Researchers determined that the 70-kilometer-wide Yarrabubba crater in Australia formed when an asteroid hit Earth just over 2.2 billion years ago. The collision occurred at a time when the planet was believed to be enveloped in ice and the impact may have caused climate warming that led to a global thaw.
"Looking at our planet from space, it would have looked very different," said Chris Kirkland, professor of isotopic geology at Curtin University in Australia, one of the researchers for the study published in the journal Nature Communications. "… You would see a white ball, not our familiar blue marble."
The researchers suspect that the region was covered by a layer of ice up to 5 km thick at the time. They calculated that the violent asteroid attack may have turned immense amounts of ice into water vapor – sending perhaps 200 billion tons of it into the atmosphere. It would be a greenhouse gas that retained heat in the atmosphere.
Researchers are wondering if this thaw helped herding the Earth to a more favorable climate for the simple microbes that inhabited the planet at the time to thrive and evolve, possibly making it a crucial event in the history of life on Earth.
The planet descended in one of its two primordial periods of the "snowball on Earth" 2.4 billion years ago, amid an increase in oxygen in an atmosphere previously dominated by methane and carbon dioxide. The asteroid, estimated to be 4-1 / 2 miles (7 km) wide, landed in Yarrabubba, Western Australia, coinciding with the end of the deep freeze.
"During the time of Yarrabubba's impact, life was simpler, but it contained organisms like stromatolites, mounds of algae that still exist today," said lead author of the study, Timmons Erickson, NASA scientist at Johnson's Astromaterials Research and Exploration Space Center. Science division.
"It is curious to think of an asteroid impact changing the Earth's atmosphere to something more lifelong than a" snowball "scenario," added Erickson.
The researchers determined the age of the crater by examining small crystals of the monazite and zircon minerals formed on the impact of the asteroid.
Earth has been hit by space rocks many times since it was formed 4.5 billion years ago. For example, an asteroid wiped out dinosaurs 66 million years ago. But the relentless movement of Earth's tectonic plates and surface erosion have erased most of the older craters. Until now, the oldest known impact crater was one in South Africa with a diameter of more than 200 kilometers that formed just over 2 billion years ago.
The other “snowball on Earth” period lasted from 700 to 600 million years ago.
Reporting by Will Dunham; Editing by Sandra Maler
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