Earth experienced a firestorm of multiple meteor impacts 790,000 years ago, a new study finds. Researchers gathered their data from analysis of tektites, pieces of natural glass formed as material from the Earth is lifted high into the atmosphere by asteroid impacts and heats on reentry.
Heidelberg University researchers examined the gravel-sized impact remnants using a new dating technique. Material was gathered from several sites around the world, including from sites in Australia, Canada, Central America and Asia. The investigators were surprised to find that, despite the fact that these samples possessed radically different chemical compositions, they all appeared to be roughly the same age. This strongly suggests that a series of impacts occurred all over the Earth at around the same time.
Researchers measured levels of various isotopes in the rocks, in an effort to determine the age of the impacts. A new method of measuring levels of isotopes of argon allowed investigators to measure the ages of these tektites with unparalleled accuracy. Analysis revealed an age for these artifacts of 793,000 years, give or take 8,000 years.
"That's how we know when, where and how often projectiles struck the earth, and how big they were," said Mario Trieloff of Heidelberg University.
The Darwin Crater in Tasmania, around 0.75 miles in diameter, was likely formed by one of these associated impacts. The meteor responsible for this basin was at least 0.6 miles across, resulting in a blast equal to one million megatons of TNT. This is 20,000 times as powerful as the largest hydrogen bomb ever developed. Investigators believe this event resulted in the formation of earthquakes and fires in areas hundreds of miles away from the impact site. This blast also lifted vast quantities of dust into the air, blocking sunlight from reaching the surface of the planet, causing plant life to die back.
Chemistry of the tektites recovered from Australia, Canada and the Antarctic was similar to one another, suggesting a single "flight path" for the extraterrestrial impactors. The specimens from Central America were chemically unique, suggesting a different source.
Previous research has provided evidence that a series of impacts occurred around the globe approximately one million years before our own time. Some of these ancient events created tektites that exist to the modern day.