Scientists may have found the oldest evidence ever of a meteorite hitting Earth: Australian scientists have discovered rock fragments 3.48 billion years old that could be the oldest evidence of a meteorite hitting Earth.
These fragments are called spherules and may have been formed by the meteor striking the ground, releasing melted rock into the atmosphere. The melted rock was then cooled and became pinhead-sized beads that were buried for many years.
This discovery was presented by researchers at the 54th Lunar and Planetary Science Conference (opens in new tab), in Texas. It has not been peer-reviewed. The scientists summarized their findings(opens a new tab) and concluded that the spherules they found in a group of volcanic and sedimentary rocks, the Dresser Formation in Western Australia, was “the oldest evidence of an Earth bolide impact” in the geologic records. A bolide is a large meteor that explodes in the atmosphere and falls to Earth.
The oldest evidence of meteor impacts was 3.47 billion-year-old spherules also from Pilbara Craton and 3.45 billion-year-old fragments in Kaapvaal Craton in South Africa.
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Chris Yakymchuk, a Canadian geologist, said in an email that “this new research documents the ejecta found in slightly older rocks” (opens in new tab), adding that he was not involved with the research. He said that the results are robust but that it would take access to all data to confirm their importance.
Scientists discovered the spherules in 2019 in cores from sedimentary rock. They were then dated using isotopes. These are versions of a chemical element with different masses. This is due to the number of neutrons within their nuclei. Yakymchuk stated that this is a reliable and robust dating method. Based on the isotope dating for the mineral zircon, we have a good idea about their age.
Due to their chemical composition, the team concluded that the spherules could be alien in origin. The team found platinum group elements such as iridium in higher quantities than is usual in terrestrial rocks. They also detected minerals called nickel-chromium spunels and isotopes of osmium within the typical range for meteorites. The fragments also had the typical dumbbell and teardrop shape of impact spherules. They also contained bubbles that form after meteorites hit.
It is often difficult to find evidence of meteor collisions with Earth. Erosion and plate tectonics wear down the crust of the planet and can erase evidence from ancient strikes such as impact craters. Scientists were heatedly arguing about a 2012 study that claimed to have found the oldest known meteor crater in the world. Sometimes, however, when geological forces destroy a crater spherules can be all that remain.