The last, dramatic moments in the life of some microbes could tell us more about how severe the impacts of space rocks on Earth were in the ancient past.
A new study suggests that the charred bodies of microorganisms killed by even a moderate asteroid impact may show the amount of damage a cosmic crash can produce.
A research team examined four craters in Estonia, Poland and Canada that were created thousands of years apart. Despite their geographic distance and the amount of time between these various impacts, the team found millimeter-sized pieces of coal mixed with the material that formed during each, the authors said.
The coal “was formed from organisms that were killed, grilled and buried by the asteroid,” lead author Anna Losiak, who works with the Institute of Geological Sciences of the Polish Academy of Sciences, told Space.com. That discovery of ancient asteroid-battered organisms differed from the coal associated with normal fires, which was the team’s main hypothesis for a while.
Related: Why is science fiction so obsessed with asteroid impact disasters (and how to stop them)?
Coal formed by impact rather than fires, he added, is “much more homogeneous and indicates a lower formation temperature.”
He said the impact coal found in the craters was similar, but not identical, to the coal that forms when wood is mixed with pyroclastic flows. (Pyroclastic flows form from erupting volcanoes.)
The smaller impact craters Losiak studied – those that are only up to 200 meters in diameter – form every 200 years or so and therefore present numerous opportunities to study formation conditions, he said.
But its goal is distinct: “Most people are interested in gigantic collisions because they are capable of causing damage on a planetary scale: the decrease in dinosaurs is the best, and so far the only, example of this type of event.” he said, referring to the asteroid event that led to the extinction of non-avian dinosaurs 66 million years ago.
In the pictures: Asteroids in deep space
Losiak first encountered mysterious coal near a small impact crater in Estonia. He started working during a summer school opportunity as a newly coined PhD. and then he returned a year later to lead a project to discover and study “paleosoil”. Paleosoil, he said, is ancient terrain covered with material removed from the crater during its formation.
As it turned out, the team never found paleosoil. But after three days of manual excavation, a time-consuming necessity due to environmental protection, his team found coal.
“At first, we thought this coal was formed from fires that happened just before the impact, and the coal just got tangled up in this extraterrestrial situation,” he said. “But later, I found similar coal in other impact craters and started thinking that something was wrong with this hypothesis.”
What seemed odd to the team, he said, was why there would be so many large fires just before the formation of four different impact craters created geographically distant from each other and over a span of thousands of years.
“It didn’t make sense, so we decided to investigate further and analyze the properties of the coal pieces found mixed within the material ejected from the craters and compare it to the fire coal,” he said. It was then that the team discovered that the fires were not 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 dangers to worry about. But Losiak said that adequate disaster preparedness will benefit from studies like his.
“This study improves our understanding of the environmental effects of the formation of small impact craters,” he 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 emerge recently in recorded history. One of the most famous examples is the Tunguska event, which leveled some 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 by 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 a region called Campo del Cielo, in late September to follow up on the search.
“We will collect more data and samples and hopefully be able to 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 when it hit 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 speed similar to that of a sniper rifle bullet, the researchers say.
“In this case, most of the asteroid survives and the temperatures and pressures experienced by the ground are much less extreme,” Losiak said. The goal is to perform “a perfect natural experiment” by comparing the craters and funnels in the same area, she added.
A research-based study was published Aug.31 in the journal Geology (opens in a new tab).
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