It is one of the largest asteroids to have slammed into Earth.
Scientists have found evidence for one of the largest asteroids to have struck Earth early in its life. In fact, it is the second oldest known to have hit the planet.
Tiny glass beads, called spherules, were found in northwestern Australia, and according to Andrew Glikson from the Australian National University (ANU) and Planetary Institute, they were formed from vaporized material from the asteroid impact.
Glikson, who is the lead author of the study, said in an ANU news release, "The impact would have triggered earthquakes orders of magnitude greater than terrestrial earthquakes, it would have caused huge tsunamis and would have made cliffs crumble."
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"Material from the impact would have spread worldwide. These spherules were found in seafloor sediments that date from 3.46 billion years ago," Glikson continued.
Photograph of rock slab displaying the densely packed spherules. Photo credit: Andrew Glikson
Scientists can determine the size of an asteroid and its impact crater using a mass balance approach for the element Osmium (Os) — a rare element in Earth’s crust, but common in asteroids.
If they know how much Osmium was in the ocean before and after the impact, scientists can calculate how much was added by the vaporization of the asteroid. Since most asteroids have a similar chemical composition, researchers can estimate how big the rest of the asteroid had to have been to add that amount of Osmium to the ocean.
This newly discovered asteroid, which was likely 12 to 19 miles (20 to 30 kilometers) across, would have created an impact crater hundreds of miles wide. However, exactly where the asteroid struck Earth “remains a mystery,” said Glikson. "Any craters from this time on Earth's surface have been obliterated by volcanic activity and tectonic movements."
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Glikson, along with Arthur Hickman from the Geological Survey of Western Australia, found the spherules in a drill core from Marble Bar, located in northwestern Australia, where some of the oldest known sediments on Earth are found. The sediment layer, which was originally on the ocean floor, was preserved between two volcanic layers. This preservation was helpful in precisely dating and determining the origin of the glass beads.
Glikson has been searching for evidence of ancient impacts for more than 20 years, and immediately suspected that the glass beads originated from an asteroid strike. Luckily, through further testing, the levels of elements, such as platinum, nickel, and chromium, matched those found in asteroids.
"This is just the tip of the iceberg. We've only found evidence for 17 impacts older than 2.5 billion years, but there could have been hundreds," explained Glikson.
Asteroid impacts likely played an important role in major tectonic shifts and magma flows, both of which significantly affected the way Earth evolved.
The research is published in the journal Precambrian Research.
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