Australia has uncovered 3,48 billion-year-old shards of rock that may be the oldest indication of a meteorite impacting Earth.

The shards, known as spherules, may have formed when the meteor struck the earth, blasting molten rock into the atmosphere. This molten rock then cooled and solidified into beads the size of pinheads, which got buried over ages.

Evidence of a meteor impacting Earth may have been discovered by scientists

This week, researchers reported this non-peer-reviewed discovery at the 54th Lunar and Planetary Science Conference(opens in new tab) in Texas. The scientists determined in a summary of their findings(opens in a new tab) that the spherules, which they extracted from the Dresser Formation of the Pilbara Craton in Western Australia, are “the earliest evidence of a probable bolide impact in the geologic record of Earth.” (A bolide is a big meteor that bursts while descending through the Earth’s atmosphere.)

Before date, the earliest evidence of meteor impacts were spherules from the Pilbara Craton that were 3.47 billion years old and pieces from the Kaapvaal Craton in South Africa that were 3.45 billion years old.

Chris Yakymchuk, a geologist at the University of Waterloo in Canada who was not involved in the study, told Live Science via email, “This new research reveals ejecta in somewhat older rocks, which have an age of 3.48 billion years (approximately 10 million years older than previously discovered).” According to him, access to the whole dataset is required to confirm the importance of the results.

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Scientists discovered spherules in sedimentary rock cores in 2019 and dated them using isotopes, which are variants of the same chemical element with differing weights according to the amount of neutrons in their nuclei. “This is a solid and trustworthy dating method,” Yakymchuk stated. Based on isotopic dating of the mineral zircon, we have a decent notion of their age.

According to their chemical makeup, the scientists determined that the spherules were virtually probably of extraterrestrial origin. They observed far larger concentrations of platinum group metals like iridium than are typically seen in terrestrial rocks, as well as nickel-chromium spinels and osmium isotopes typical of meteorites. In addition, they observed that the shards exhibited the distinctive dumbbell and teardrop forms of impact spherules and included bubbles, which tend to occur when molten rock splashes harden after a meteor impact.

Evidence of meteor impacts with Earth is difficult to locate and frequently contentious. Plate tectonics and erosion can erode the planet’s crust and obliterate evidence of ancient impacts, such as impact craters. A 2012 paper claiming to have discovered the oldest meteor crater in the world sparked a heated discussion among experts. But, when geological processes obliterate a crater, spherules are occasionally all that remains.

Yakychuk stated, “There are two groups of impact-related rocks.” “The oldest known impact crater is the 2.23 billion-year-old Yarrabubba formation in Western Australia, which is included in the first category. The second group consists of shards of rock and minerals that were formed by an impact but were afterwards expelled from the impact crater and are now present in rocks.”

The team is currently examining the rocks that enclosed the spherules and investigating the many layers of silt they bore up to further their understanding of the meteor impact. Ancient bombardments like this one altered early Earth’s circumstances and provide uncommon insights into our planet’s past.

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