The final, dramatic moments in the lives of some microbes can tell us more about how severe space rock impacts on Earth were in the ancient past.
The charred bodies of microorganisms killed by even a moderate asteroid impact may reveal the extent of the damage caused by a cosmic crash, a new study suggests.
A research team studied four craters in Estonia, Poland and Canada that formed thousands of years apart. Despite their geographical distance and the length of time between these different impacts, the team found millimeter to centimeter-sized chunks of charcoal that mixed with the material formed at each of them, the authors said.
The charcoal “was formed from organisms killed, grilled and buried by the asteroid,” lead author Anna Losiak, who works at the Institute of Geological Sciences of the Polish Academy of Sciences, told Space.com. This discovery of ancient asteroid-haunted organisms differed from charcoal associated with ordinary wildfires, which was the team’s leading hypothesis for a time.
Related: Why is science fiction so obsessed with asteroid impacts (and how to stop them)?
Charcoal formed by impact rather than wildfire, she added, is “much more homogeneous and indicates a lower temperature of formation.”
She said the impact charcoal found in the craters is similar, but not identical, to charcoal formed when wood is mixed with pyroclastic flows. (Pyroclastic flows form from erupting volcanoes.)
The smaller impact craters Losiak is studying — those that are only up to 200 meters in diameter — form about every 200 years, so provide ample opportunities to study formation conditions, she said.
But their focus is clear: “Most people are interested in gigantic collisions because they are capable of causing planet-scale damage – the depletion of the dinosaurs is the best and so far only example of this type of event,” said you. refers to the asteroid event that led to the extinction of non-avian dinosaurs 66 million years ago.
On photos: Asteroids in space
Losiak first encountered the mysterious charcoal near a small impact crater in Estonia. She began her work during a summer school as a freshly graduated Ph.D. and then returned a year later to lead a project to uncover and study the “paleosoil”. Paleosoil, she said, is ancient soil covered by the material removed from the crater during its formation.
As it turned out, the team never found the paleo bottom. But after three days of hand digging, a time-consuming environmental necessity, her team found charcoal.
“At first we thought this charcoal was from wildfires that happened just before the impact, and the charcoal just got tangled up in this extraterrestrial situation,” she said. “But later I found similar charcoal in other impact craters and began to think something was wrong with that hypothesis.”
What struck the team as odd, she said, was why there would be so many large wildfires just before the formation of four different impact craters that were geographically distant and formed over thousands of years.
“It didn’t make sense, so we decided to do further research and analyze the properties of pieces of charcoal found mixed with material ejected from craters and compare them to charcoal from wildfires,” she said. At this point, the team determined that there were no wildfires at all.
Related: Watch as California’s biggest wildfire of the year creates a massive “fire cloud” visible from space
NASA and other agencies are constantly on the lookout for extraterrestrial bodies such as comets or asteroids that could create a crater on the Earth’s surface. So far, scientists have not identified any imminent dangers to worry about. But Losiak said proper disaster preparedness will benefit from studies like hers.
“This study improves our understanding of the environmental impact of small impact crater formation,” she said. For incoming impactors, she added, “We will be able to more accurately determine the size and type of evacuation zone required.”
Relatively large impact events appear 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.
Recently, in 2014, a small body exploded over the Russian city of Chelyabinsk. Thousands of people were injured by glass and other debris, but otherwise damage was minimal.
Losiak and her team plan to go to another group of small impact craters in Argentina in a region called Campo del Cielo in late September to continue the research.
“We will collect more data and samples and hopefully find more organisms that were killed by the asteroids,” Losiak said. “Campo del Cielo is particularly interesting because there are not only real impact craters – places where an asteroid literally exploded when it hit the ground – but also impact craters.”
A penetration funnel forms when an asteroid slows down in the atmosphere as it enters Earth. This formation occurs when it hits the ground at a speed similar to a sniper rifle bullet, the researchers say.
“In this case, most of the asteroid survives and the temperatures and pressures that the ground experiences are much less extreme,” Losiak said. The goal is to do “a perfect natural experiment” by comparing the craters and funnels in the same area, she added.
A study based on the research was published Aug. 31 in the journal Geology (opens in new tab).
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