IMPACT STUDIES
Crime-scene technique identifies asteroid sites
Analysing the charred remains of plants can confirm the locations of asteroid strikes in the distant past, new research shows.
Based on estimates of crater-producing asteroid strikes in the last 11,650 years (known as the Holocene), only about 30% of impact sites have been located.
Until now, there has been no way to distinguish between normal land 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 wildfire charcoal – so analysing samples allows scientists to work out the origin of small craters.
"The properties of organisms turned 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.
"Those conditions, such as the heat the wood was exposed to or the duration of the heating, leave tell-tale signs in the material’s structure.
"For example, charcoal from low-energy surface fires, like burning bushes and leaves, has different properties than charcoal from high-intensity wildfires.
"Impact charcoals are very strange. They all look as if they were formed in much lower temperatures than wildfire charcoals, and they are all very similar to each other, while in a wildfire it is common to find strongly charred wood just next to barely affected branches."
Dr Losiak worked on the research as part of a Marie Sklodowska-Curie Individual Fellowship at the University of Exeter wildFIRE lab, led by Professor Claire Belcher.
The research team dug trenches in 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 proved to be dramatic and surprising," said Professor Belcher, part of Exeter's Global Systems Institute.
"While wildfire charcoal is considerably varied in its reflectivity, depending on the local conditions during the fire, impact charcoals showed uniform characteristics despite coming from completely different locations and being formed thousands of years apart.
"This presents an opportunity for geologists looking for unrecognised impact craters."
Professor Chris Herd, from the University of Alberta, said: "This study improves our understanding of environmental effects of small impact crater formation so that in the future, when we discover an asteroid a few metres across or more coming our way only a couple of weeks before the impact, we will be able to more precisely determine the size and type of evacuation zone necessary."
Dr Losiak added: "Since 1900, two impacts – in Tunguska and Chelyabinsk – caused damage on a massive scale.
"In order to prepare for any future threats, we need to understand how often collisions like that occur.
"And to do that, we need to look to our planet’s recent past."
The paper, published in the journal Geology, is entitled: "Small impact cratering processes produce distinctive charcoal assemblages."
JOURNAL
Geology
DOI
CAPTION
Looking for charcoal (by Juri Plado).
CREDIT
Juri Plado
CAPTION
Finding charcoal within Kaali 2-8 crater ejecta (by Juri Plado).
CREDIT
Juri Plado
Death from space
New Geology Science published online ahead of print
Peer-Reviewed PublicationIMAGE: DIGITAL ELEVATION MODEL OF KAALI CRATERS (BY ARGO JÕELEHT). view more
CREDIT: ARGO JÕELEHT
Boulder, Colo., USA: Tens of tons of extraterrestrial solid material collide with Earth daily. Most of this material is small enough that it burns up in the atmosphere, but some fragments are large enough to cause quite a predicament. In 2013, a 20-meter-diameter body exploded over Chelyabinsk, seriously injuring more than 1,500 people. The most recent impact crater on Earth was formed in 2007, when an asteroid crashed into a small village in Peru. A 1947 asteroid impact in far-eastern Russia resulted in the formation of the youngest crater-strewn field on our planet: Sikhote-Alin. The most impressive, relatively recent, extra-terrestrial event happened in 1908, when a body exploded over Siberia, flattening 2000 km2 of forest. We can prepare for this natural hazard only if we understand how often these kinds of small impacts happened in the past and how they influenced the environment.
A new article in the Geological Society of America’s journal Geology shows that analyzing bodies of organisms killed by an impact of asteroids can teach us exactly how much damage occurs at the spot of such a cosmic collision. The research team dug out trenches in rims of four craters (Kaali Main and Kaali 2/8 in Estonia, Morasko, in Poland, and Whitecourt in Alberta, Canada), located on two different continents that formed thousands of years apart.
Dr. Jüri Plado and Dr. Argo Jõeleht noticed, “Surprisingly, in all those places we found the same thing: millimeter- to centimeter-sized pieces of charcoal intermixed within material ejected during its formation and located at the same place in respect to the crater.
Dr. Ania Losiak, the lead author of this study, from the Institute of Geological Sciences, Polish Academy of Sciences, and the University of Exeter, said, “At first we thought those charcoals were formed by wildfires that occurred shortly before the impact, and charcoals just got tangled in this extraterrestrial situation. But something was not right with this hypothesis—there were too many coincidences; why would there be large wildfires shortly before formation of four different small impact craters divided by thousands of kilometers and years? Why would it be found only in a very specific location within the proximal ejecta blanket? It made no sense, so we decided to investigate further and analyze properties of charcoal pieces found intermixed within material ejected from craters and compare it with wildfire charcoals.”
Like bodies studied in a criminal investigation, the properties of organic remnants turned into charcoal reflect the conditions in which they were killed. Based on their properties, we can clearly recognize charcoals formed as a result of a wildfire and those found within proximal ejecta of impact craters. Professor Claire Belcher from the University of Exeter explained, “Impact charcoals are really weird: They were all formed in much lower temperatures than wildfire charcoals, they lack sections that were formed while directly touching the flame, and they are all very similar to each other, while in a fire it is common to find strongly charred wood just next to barely affected branches.”
“This is definitely not what we expected when we started this study: We think that impact charcoals were formed when fragments of trees shattered by the impact were intermixed with local material ejected from the crater,” added Losiak.
“This study improves our understanding of environmental effects of small impact crater formation so that in the future, when we discover an asteroid a few meters across or more coming our way only a couple of weeks before the impact, we will be able to more precisely determine the size and type of evacuation zone necessary,” said Professor Chris Herd from the University of Alberta.
“Our research may also help to find new impact craters on Earth; we expect that we are missing from our records more than ten craters formed within the last ten thousand years. We need to find them, before their relatives visit us unexpectedly,” explained professor Witek Szczuciński from Adam Mickiewicz University in Poznan.
Charcoal with wood structure preserved on which it is possible to recognize the type of a tree killed by an asteroid. Image under Scanning Electron Microscope (by Ania Losiak).
CREDIT
Ania Losiak
Fragment of organism killed and baked alive by an asteroid (picture under optical microscope by Ania Losiak).
CREDIT
Ania Losiak
FEATURED ARTICLE
Small impact cratering processes produce distinctive charcoal assemblages
Anna Losiak; Claire Belcher; Christopher Herd; Witold Szczucinski; Sarah Baker; Randolf Kofman; Juri Plado; Argo Joeleht; Monika Szokaluk; Andrzej Muszynski; Ewa Wild
Dr Ania Losiak, Institute of Geological Sciences ,Polish Academy of Sciences, Wroclaw, Poland, and University of Exeter, UK, anna.losiak@twarda.pan.pl, +48 660535657.
Prof. Christopher Herd, Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Canada, herd@ualberta.ca, +1 7807078217
URL: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G50056.1/616545/Small-impact-cratering-processes-produce
GEOLOGY articles are online at https://geology.geoscienceworld.org/content/early/recent . Representatives of the media may obtain complimentary articles by contacting Kea Giles at the e-mail address above. Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GEOLOGY in articles published. Non-media requests for articles may be directed to GSA Sales and Service, gsaservice@geosociety.org.
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JOURNAL
Geology
ARTICLE TITLE
Small impact cratering processes produce distinctive charcoal assemblages
ARTICLE PUBLICATION DATE
31-Aug-2022
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