Crime scene technique identifies asteroid sites

Analysis of charred remains of plants can confirm locations of asteroid strikes in the distant past, new research suggests.

Based on estimates of crater-producing asteroid impacts over the past 11,650 years (known as the Holocene), only about 30% of impact sites have been located.

Until now, there was no way to distinguish between normal Earth structures and very small asteroid craters, unless pieces of iron meteorites were found nearby.

In the new study, an international team of researchers found that charcoal around craters is different from charcoal from wildfires. Thus, the analysis of samples allows scientists to determine the origin of small craters.

“The properties of organisms transformed into charcoal reflect the conditions in which they were killed,” said lead author Dr Ania Losiak, from the Institute of Geological Sciences, Polish Academy of Sciences and the University of Exeter.

“These conditions, such as the heat the wood has been exposed to or the duration of heating, leave telltale signs in the structure of the material.

“For example, charcoal from low-energy surface fires, such as burning bushes and leaves, has different properties than charcoal from high-intensity wildfires.

“Impact charcoals are very strange. They all seem to have formed at much lower temperatures than wildfire charcoals, and they are all very similar to each other, whereas in a wildfire forest, it is common to find heavily charred wood right next to barely affected branches.”

Dr Losiak worked on the research under a Marie Sklodowska-Curie Individual Fellowship at the University of Exeter’s wildFIRE laboratory, led by Professor Claire Belcher.

The research team dug trenches in the rims of four craters (Kaali Main and Kaali 2/8 in Estonia, Morasko in Poland and Whitecourt in Canada).

“The differences between wildfire charcoal and impact charcoal have been found to be dramatic and surprising,” said Professor Belcher, who is from the Global Systems Institute in Exeter.

“While wildfire charcoal varies widely in its reflectivity, depending on local conditions during the fire, impact charcoals showed uniform characteristics despite coming from completely different places and being formed thousands of years apart.

“This presents an opportunity for geologists searching for unrecognized impact craters.”

Professor Chris Herd, from the University of Alberta, said: “This study improves our understanding of the environmental effects of the formation of small impact craters so that in the future, when we discover an asteroid of a few meters in diameter or more coming our way, only a few weeks before impact, we will be able to more accurately determine the size and type of evacuation zone needed.”

Dr Losiak added: “Since 1900, two impacts – at Tunguska and Chelyabinsk – have caused large-scale damage.

“In order to prepare for any future threat, we need to understand how often such collisions occur.

“And to do that, we have to look to our planet’s recent past.”

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Materials provided by University of Exeter. Note: Content may be edited for style and length.