A 3,300-foot- (1 km) wide asteroid struck our planet 1.2 billion years ago, according to new research published in the Journal of the Geological Society.
An artist’s depiction of an asteroid impact. Image credit: Don Davis / NASA.
In 2008, a team of researchers from the Universities of Oxford and Aberdeen found evidence for the ancient meteorite strike near Ullapool, Scotland.
The thickness and extent of the debris deposit the scientists found suggested the impact crater was close to the coast, but its precise location remained a mystery.
Now University of Oxford’s Dr. Ken Amor and colleagues have identified the crater location 9.3-12.3 miles (15-20 km) west of a remote part of the Scottish coastline.
“The material excavated during a giant meteorite impact is rarely preserved on Earth, because it is rapidly eroded, so this is a really exciting discovery,” Dr. Amor said.
“It was purely by chance this one landed in an ancient rift valley where fresh sediment quickly covered the debris to preserve it.”
Using a combination of field observations, the distribution of broken rock fragments known as basement clasts and the alignment of magnetic particles, the team was able to gauge the direction the meteorite material took at several locations, and plotted the likely source of the crater.
“About 1.2 billion years ago most of life on Earth was still in the oceans and there were no plants on the land,” the scientists said.
“At that time Scotland would have been quite close to the equator and in a semi-arid environment. The landscape would have looked a bit like Mars when it had water at the surface.”
“Earth and other planets may have suffered a higher rate of meteorite impacts in the distant past, as they collided with debris left over from the formation of the early Solar System.”
However, there is a possibility that a similar event will happen in the future given the number of asteroid and comet fragments floating around in the Solar System.
Much smaller impacts, where the meteorite is only a few meters across are thought to be relatively common perhaps occurring about once every 25 years on average.
It is thought that collisions with an object about 3,300 feet across occur between once every 100,000 years to once every one million years.
“It would have been quite a spectacle when this large meteorite struck a barren landscape, spreading dust and rock debris over a wide area,” Dr. Amor said.
A related study by researchers from the National Museums Northern Ireland and the University of Würzburg reached the same conclusions. The results were published in the same issue of Journal of the Geological Society.
_____
Kenneth Amor et al. The Mesoproterozoic Stac Fada proximal ejecta blanket, NW Scotland: constraints on crater location from field observations, anisotropy of magnetic susceptibility, petrography and geochemistry. Journal of the Geological Society, published online June 10, 2019; doi: 10.1144/jgs2018-093
Michael J. Simms & Kord Ernstson. A reassessment of the proposed ‘Lairg Impact Structure’ and its potential implications for the deep structure of northern Scotland. Journal of the Geological Society, published online June 9, 2019; doi: 10.1144/jgs2017-161
