An international team of scientists from South Korea and Australia has found evidence of a major asteroid impact that occurred approximately 3.5 billion years ago (Archean era).
Tiny impact spherule from Duffer Formation, Australia. Image credit: Andrew Glikson et al.
Australian National University researcher Dr. Andrew Glikson and co-authors found small glass beads called spherules in a drill core from the volcanic Duffer Formation in Pilbara region of Western Australia, in some of the oldest known sediments on Earth.
The sediment layer, which was originally on the ocean floor, was preserved between two volcanic layers, which enabled very precise dating of its origin.
The scientists immediately suspected the spherules originated from an asteroid strike, and subsequent testing found the levels of elements such as platinum, nickel and chromium matched those in asteroids.
“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,” said Dr Glikson, lead author on a study published in the July 2016 issue of the journal Precambrian Research.
“Material from the impact would have spread worldwide. These spherules were found in sea floor sediments that date from 3.46 billion years ago.”
The asteroid is the second oldest known to have hit the Earth and one of the largest.
“The asteroid would have been 15 miles (25 km) across and would have created a crater hundreds of miles wide,” Dr. Glikson said.
“Exactly where this asteroid struck the Earth remains a mystery.”
“Any craters from this time on Earth’s surface have been obliterated by volcanic activity and tectonic movements.”
“There may have been many more similar impacts, for which the evidence has not been found,” Dr. Glikson said.
“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.”
“Asteroid strikes this big result in major tectonic shifts and extensive magma flows. They could have significantly affected the way the Earth evolved.”
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Andrew Glikson et al. 2016. A new ∼3.46 Ga asteroid impact ejecta unit at Marble Bar, Pilbara Craton, Western Australia: A petrological, microprobe and laser ablation ICPMS study. Precambrian Research, vol. 279, pp. 103-122; doi: 10.1016/j.precamres.2016.04.003
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