Earliest Proof of Meteorite Impact on Earth Found by Scientists

Australian scientists have discovered rock fragments 3.48 billion years old that could be the first evidence of a meteorite hitting Earth.

The fragments, known as balls, may have formed when the meteorite hit the ground, spewing molten rock into the air. This molten rock then cooled and solidified into pinhead-sized grains that were buried over the centuries.

Scientists made this discovery, which was not peer-reviewed, in Fifty-fourth Congress of Lunar and Planetary Sciences in Texas last week. Summarizing their findings, the scientists concluded that the pellets they recovered from a group of igneous and sedimentary rocks called the Dresser Formation in Western Australia’s Pilbara Craton are “the oldest evidence of a possible meteorite impact by an explosion in the Earth’s geological record.” (A meteoroid is a large meteorite that explodes in the atmosphere as it hits the ground.)

To date, the oldest evidence of meteorite impacts are 3.47 billion year old balls also found in the Pilbara craton and 3.45 billion year old fragments found in the Kawal craton in South Africa.

Scientists discovered the globules in 2019 in the core of sedimentary rocks and dated them using isotopes, which are versions of the same chemical element that have different masses due to the number of neutrons in their nuclei.

“It’s a robust and reliable dating method,” said Chris Yakimchuk, a geologist at the University of Waterloo in Canada who was not involved in the study. “We have a pretty good idea of ​​their age based on isotopic dating of the mineral zircon.”

The team concluded that the globules were almost alien in origin due to their chemical composition. They found elements of the platinum group, such as iridium, in much greater amounts than are commonly found in terrestrial rocks, as well as minerals called spinel. Nickel, chromium, and osmium isotopes are within the typical range for most meteorites.

They also note that the fragments are characteristically shaped like a dumbbell and impact pellet blobs, and contain bubbles that tend to form when molten spots solidify after a meteorite impact.

Evidence for meteorite impacts on Earth is hard to come by and is often controversial. Plate tectonics and erosion are eroding the planet’s crust and can obliterate ancient impacts such as impact craters.

A 2012 study claiming to have discovered the world’s oldest meteorite crater sparked a heated debate among scientists. But when geological forces erase the crater, sometimes only balls remain from this event.

“There are two groups of rocks associated with impact,” Yakimchuk explained. where there are fragments of rocks and minerals that were formed as a result of the impact. But it was ejected from the impact crater and is now in the rocks.”

The team is currently studying the rocks that encased the balls and analyzing the different layers of sediment they dug up to better understand meteorite impacts.

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