A new study led by Curtin researchers shows that the five large meteorite impacts from the famous 4,500 km-long North America and Europe crater-chain, postulated to have happened within seconds, actually occurred randomly over a period of tens of millions of years.
The research also concludes that the craters are not related to each other, and neither caused any species extinction.
A well-accepted hypothesis in Earth Sciences suggested that Earth saw a cataclysmic multiple impact event roughly 214 million years ago in Late Triassic time. According to a 1998 Nature study, this event was probably similar to the synchronous impacts of several fragments of comet Shoemaker-Levy 9 on the surface of Jupiter in 1994.
Five large asteroid impacts were thought to have produced impact craters across North America and Europe within seconds.
The former study concluded that the alignment was considered extremely unlikely to be the result of a series of random strikes, given agreeing geologic ages for the impacts available years ago.
The latest study, led by Curtin geologist Dr Martin Schmieder and carried out alongside Associate Professor Dr Fred Jourdan from Curtin University and Dr Eric Tohver of The University of Western Australia in Perth, was recently published in the journal Earth and Planetary Science Letters.
Dr Schmieder said the study explores the age of the 40 km-wide Lake Saint Martin impact structure in Canada, one of the candidate craters thought to have been formed during the giant multi-impact strike.
“Lake Saint Martin is one of the best-preserved large impact craters on our planet, but it is for some reason not well known in the public, probably because the crater itself is buried underneath younger sediments and water, and is therefore not visible as a real crater in a rather flat landscape,” Dr Schmieder said.
“However, our colleague Dr Ed Cloutis from the University of Winnipeg managed to sample fresh crater rocks that we could use for a new dating attempt.”
The new age data was obtained using an argon mass spectrometer at the Western Australian Argon Isotope Facility at Curtin University.
Laboratory director Dr Fred Jourdan said “We used different impact-melted rocks and minerals from different localities within the crater to arrive at a fairly precise and meaningful argon-argon age of about 228 million years.”
Previous age dating of the aligned impact craters had produced overlapping ages with relatively large error bars, allowing for the hypothetical crater chain scenario.
“Until recently, an uncertainty of 64 million years was associated with the age of the Lake Saint Martin impact, but the new age from our lab has only two million years of error. Modern argon-argon dating can literally nail down the ages for large meteorite impacts, not only on Earth but also on other planets and even on asteroids,” Dr Jourdan said.
Dr Schmieder and his colleagues combined these new data with previous recent dating results from other craters in the chain, including some earlier dating carried out by Dr Schmieder, and concluded that none of the craters are even remotely connected.
“The differing refined crater ages are strong evidence that the Late Triassic multiple impact event never happened. Several million years lie between each of these asteroid impacts,” Dr Jourdan said.
Further information and reading
Martin Schmieder, Fred Jourdan, Eric Tohver & Edward A. Cloutis (2014): 40Ar/39Ar age of the Lake Saint Martin impact structure (Canada) – Unchaining the Late Triassic terrestrial impact craters – Earth and Planetary Science Letters 406, 37–48.