A team of researchers from Australian National University (ANU) has discovered evidence of a massive asteroid that collided with the Earth in its early life in the form of tiny glass beads called spherules. These spherules were discovered in northwestern Australia and created through the vaporization of material from the impact, which was larger than anything humans have ever experienced.
"The impact would have triggered earthquakes orders of magnitude greater than terrestrial earthquakes, it would have caused huge tsunamis and would have made cliffs crumble," said Andrew Glikson from the ANU Planetary Institute and lead author of the study. "Material from the impact would have spread worldwide. These spherules were found in sea floor sediments that date from 3.46 billion years ago."
In addition to being one of the largest asteroids to hit the Earth - an estimated 20 to 30 kilometers across that likely led to a hundred-kilometer-wide crater - it is also the second oldest known.
Around 3.8 to 3.9 billion years ago, prior to the collision of the asteroid collision examined in the current ANU study, the moon was hit by numerous asteroids that created craters called mare that can still be seen from the Earth.
"Exactly where this asteroid struck the earth remains a mystery," Glikson said. "Any craters from this time on Earth's surface have been obliterated by volcanic activity and tectonic movements."
Glikson, along with Arthur Hickman from the Geological Survey of Western Australia, discovered glass beads in a drill core from Marble Bar, located in northwestern Australia. The sediment layer, which originates from the ocean floor, provided them with some of the oldest sediments known on the Earth and allowed for extremely precise origin dates.
The team tested the sediments and discovered levels of elements such as platinum and nickel that aligned with those in asteroids, suggesting an impact. Furthermore, Glikson believes that there might have been other similar impacts that we have yet to discover.
"This is just the tip of the iceberg," he said. "We've only found evidence for 17 impacts older than 2.5 billion years, but there could have been hundreds. Asteroid strikes this big result in major tectonic shifts and extensive magma flows. They could have significantly affected the way the Earth evolved."
The findings were published online April 9 in the journal Precambrian Research.
