The dramatic last moments in the life of certain microbes can tell us more about the severity of the impacts of space rocks on Earth in the ancient past.
The charred bodies of microorganisms killed by even a moderate asteroid impact can show the extent of damage from a cosmic crash, a new study has found.
A research team has examined four craters in Estonia, Poland and Canada that were created thousands of years apart. Despite their geographic distance and the time elapsed between these different impacts, the team found millimeter to centimeter-sized lumps of charcoal mixed with the material that formed during each of them, the authors said.
The charcoal “was formed from organisms killed, roasted and buried by the asteroid,” lead author Anna Losiak, from the Institute of Geological Sciences at the Polish Academy of Sciences, told Space.com. science. This finding of ancient organisms battered by asteroids differed from the charcoal associated with normal wildfires, which was the team’s primary hypothesis for some time.
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Charcoal formed by impact instead of wildfire, she added, is “much more homogeneous and indicates a lower formation temperature.”
She said the impact charcoal found in craters was similar, but not identical, to the charcoal that forms when wood is mixed with pyroclastic flows. (Pyroclastic flows form from erupting volcanoes.)
The smallest impact craters studied by Losiak – those as small as 200 meters in diameter – form about every 200 years and thus provide many opportunities to study the conditions of formation, she said.
But his focus is distinct: “Most people are interested in gigantic collisions because they are capable of causing planet-wide damage – dinosaur shrinkage is the best, and so far the only one. example of this type of event,” she said. referring to the asteroid event that led to the extinction of non-avian dinosaurs 66 million years ago.
In picture : Asteroids in deep space
Losiak first discovered the mysterious charcoal near a small impact crater in Estonia. She started working on a summer school opportunity as a newly created doctoral student. then returned a year later to lead a project to discover and study the “paleosol”. Paleosol, she said, is ancient soil covered by the material removed from the crater when it was formed.
It turned out that the team never found the paleosol. But after three days of digging by hand, a time-consuming necessity due to environmental protection, his team found charcoal.
“At first, we thought this charcoal was formed by forest fires that happened shortly before impact, and the charcoal just got tangled up in this extraterrestrial situation,” he said. she declared. “But later I found similar charcoal in other impact craters and started to think something was wrong with that assumption.”
What seemed strange to the team, she said, was why there would be so many large wildfires shortly before the formation of four different impact craters created geographically distant from each other. and over a period of several thousand years.
“It made no sense, so we decided to investigate further and analyze the properties of the pieces of charcoal found mixed in materials ejected from the craters, and compare them with firewood charcoal from forest,” she said. That’s when the team discovered that wildfires weren’t involved at all.
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NASA and other entities are continually searching for extraterrestrial bodies, such as comets or asteroids, that could cause a crater on the Earth’s surface. So far, scientists have found no imminent danger to fear. But Losiak said good disaster preparedness would benefit from studies like his.
“This study improves our understanding of the environmental effects of the formation of small impact craters,” she said. For incoming impactors, she added, “we will be able to more accurately determine the size and type of evacuation zone needed.”
Relatively large impact events are cropping up recently in recorded history. One of the most famous examples is the Tunguska event, which razed about 770 square miles (2,000 square kilometers) of Siberian forest in 1908.
More recently, in 2014, a small body exploded over the Russian city of Chelyabinsk. Thousands of people were injured from the glass and other debris, but otherwise the damage was minimal.
Losiak and his team plan to travel to another set of small impact craters in Argentina, in an area called Campo del Cielo, in late September to continue the search.
“We will collect more data and samples, and hopefully we can find more organisms killed by asteroids,” Losiak said. “Campo del Cielo is particularly interesting because there are not only real impact craters – sites where an asteroid literally exploded upon hitting the ground – but also penetration funnels.”
A penetration funnel occurs when an asteroid slows down in the atmosphere as it enters Earth. This formation occurs when it hits the ground with a velocity similar to that of a sniper rifle bullet, researchers said.
“In this case, most of the asteroid survives, and the temperatures and pressures experienced by the ground are much less extreme,” Losiak said. The aim is to achieve “a perfect natural experiment” by comparing craters and funnels in the same area, she added.
A study based on the research was published on August 31 in the journal Geology (opens in a new tab).