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.