Scientists in Australia have unearthed 3.48 billion-year-old rock fragments that may be the earliest evidence of a meteorite crashing into Earth. The fragments, known as spherules, may have formed when the meteoroid slammed into the ground, spraying melted rock into the air. This melted rock then cooled and hardened into pinhead-size beads that became buried over the aeons. The scientists concluded that the spherules, which they drilled up from a group of volcanic and sedimentary rocks called the Dresser Formation of the Pilbara Craton in Western Australia, are “the oldest evidence of a potential bolide impact in the geologic record of Earth.” A bolide is a large meteoroid that explodes in the atmosphere while falling to Earth.
Until now, the oldest evidence of meteoroid impacts were 3.47 billion-year-old spherules, also from Pilbara Craton, and 3.45 billion-year-old fragments found in Kaapvaal Craton, in South Africa. “This new research documents ejecta in slightly older rocks, which have an age of 3.48 billion years old (about 10 million years older than previously found),” Chris Yakymchuk, a geologist at the University of Waterloo in Canada who was not involved in the research, said.