Evrim Yazgin
Cosmos science journalist
New geological evidence from Scotland rewrites history books and suggests that meteorite impacts could have helped some ancient life to colonise land.
A massive meteorite hit what is today northwestern Scotland 990 million years ago (mya) – about 200 million years later than previously thought – according to research published in the journal Geology.
The billion-year-old impact created a layer of rock known as the Stac Fada Member. It had previously been estimated that the layer was 1.2 billion years old.
New analysis of tiny zircon crystals has seen this age revised.
“These microscopic crystals recorded the exact moment of impact, with some even transforming into an incredibly rare mineral called reidite, which only forms under extreme pressures,” says lead author Chris Kirkland from Western Australia’s Curtin University. “This provided undeniable proof that a meteorite strike caused the Stac Fada deposit.”
“When a meteorite hits, it partially resets the atomic clocks inside the zircon crystals and these ‘broken timepieces’ are often unable to be dated but we developed a model to reconstruct when the disturbance occurred, confirming the impact at 990 million years ago,” Kirkland explains.
“While the impact crater itself has yet to be found, this study has collected further clues that could finally reveal its location,” Kirkland adds.
Not only was the date of the impact revised. The study also adds new insights into how the first land-based organisms evolved.
The first vertebrates to walk on land – ancestors of humans – lived nearly 400 mya. They were beaten to land by arthropods – ancestors of modern insects and spiders – which first walked on land about 425 mya. And plants began to colonise land about 470 million years ago.
But single-celled organisms made the transition out of Earth’s ancient seas much, much earlier.
Kirkland’s team found evidence of freshwater eukaryotes – single-celled ancestors of plants, animals and fungi – which moved out of marine environments about the same time as the billion-year-old meteorite impact.
“The revised dating suggests these life forms in Scotland appeared at a similar time to a meteorite impact,” Kirkland says. “This raises fascinating questions about whether large impacts may have influenced environmental conditions in ways that affected early ecosystems.
“Understanding when meteorite impacts occurred helps us explore their potential influence on Earth’s environment and the expansion of life beyond the oceans.”
