Scientists in Australia have discovered 3.48-billion-year-old rock fragments that may be the first evidence of a meteorite hitting Earth.
Pieces known as spheres may have formed when the meteorite crashed to the ground and spewed molten rock into the air. This molten rock then cooled and solidified into pinhead-sized particles that became embedded over time.
The scientists presented the non-peer-reviewed discovery at the 54th Lunar and Planetary Science Conference in Texas last week. In a summary of their findings, the scientists concluded that the nodules they excavated from a group of igneous and sedimentary rocks called the Dresser Formation in the Pilbara Craton in Western Australia are “the earliest evidence of a possible eruption meteorite impact on Earth’s geological record. .” (A meteorite is a large meteorite that explodes in the atmosphere when it hits the ground.)
To date, the earliest evidence of meteorite impacts are 3.47 billion year old pellets also found in the Pilbara Craton and 3.45 billion year old fragments found in the Kapval Craton in South Africa.
Scientists discovered globules in sedimentary rock cores in 2019 and dated them using isotopes of the same chemical element that have versions with different masses due to the number of neutrons in their cores.
“This is a solid and reliable dating strategy. Based on isotopic dating, we have a good idea of their age,” said geologist Chris Yakimchuk of the University of Waterloo in Canada, who was not involved in the study. the mineral zircon.”
The team concluded that the globules were almost certainly from another country because of their chemical composition. They discovered higher amounts of platinum group elements such as iridium, as well as minerals called spinel, in higher quantities than are normally found in terrestrial rocks. The isotopes of nickel, chromium, and osmium are in the typical range for most meteorites.
They also noted that the pieces have the characteristic shapes of a dumbbell and teardrop from impact pellets, and contain bubbles that likely form when molten layers solidify after a meteorite impact.
Evidence of meteorites hitting Earth is hard to find and often controversial. Plate tectonics and erosion erode the planet’s crust and can erase traces of ancient impacts such as impact craters.
A 2012 study that allegedly revealed the world’s oldest meteorite crater sparked a heated debate among scientists. But when geological forces sweep away a crater, sometimes all that’s left are the canyons.
“There are two groups of stones associated with the impact. The first group is where an impact crater is still preserved, the oldest being the 2.23 billion year old Yarrapopa structure in Western Australia. The second group is where rock fragments and minerals are formed.”
The team is now examining the rocks surrounding the balls and examining the different layers of sediment they excavated to better understand the meteorite’s impacts.
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