A 70-kilometer-wide crater in Western Australia has officially earned the title of Earth’s oldest known recorded impact. Yarrabubba crater is a spry 2.2 billion years old, plus or minus 5 million years, researchers report January 21 in Nature Communications.
Moving tectonic plates along with erosion have wiped away much of the evidence for many craters older than 2 billion years, leaving a gap in our understanding of how long-ago meteorite impacts may have affected the planet’s life and atmosphere (SN: 12/18/18). Scientists have uncovered ancient impact material older than 2.4 billion years from sites elsewhere in Western Australia and South Africa, but no corresponding craters.
Yarrabubba, located on one of Earth’s oldest patches of crust called Yilgarn craton, adds more than 200 million years to the impact record. The previous record-holder was Vredefort crater in South Africa.
Scientists had estimated Yarrabubba to be between 2.6 billion and 1.2 billion years old, based on previous research dating rocks around the impact site. In the new study, researchers pinpointed the crater’s age by dating microstructures in crystallized rock that formed when the impact occurred.
Dating Earth’s oldest crater was not the only exciting finding, says study coauthor Timmons Erickson, a geologist at NASA’s Astromaterials Research & Exploration Science Division in Houston. The crater’s age puts the impact at the end of an ancient glacial period. A computer simulation suggests that a Yarrabubba-sized impact would have released up to 200 trillion kilograms of water vapor into the atmosphere, which the researchers say could have warmed the planet and melted ice sheets.
Yarrabubba crater sits on one of the most ancient pieces of Earth’s crust, called Yilgarn craton in Western Australia. Stars indicate locations where rock samples were taken; the dotted line marks a magnetic signature that researchers used to identify the deeply buried center of the crater.