The last, dramatic moments of some microbes' lives may tell us more about
how serious space rock impacts on Earth were in the ancient past.
The charred bodies of microorganisms killed by even a moderate asteroid
impact can show the amount of damage produced by a cosmic crash, a new study
suggests.
A research team examined four craters in Estonia, Poland and Canada that
were created thousands of years apart. Despite their geographical distance
and the amount of time between these various impacts, the team found
millimeter-to-centimeter sized pieces of charcoal mixed in with the material
that was formed during each of them, the authors said.
The charcoal "was formed from organisms killed, grilled and buried by the
asteroid," lead author Anna Losiak, who is with the Institute of Geological
Sciences at the Polish Academy of Sciences, told Space.com. That discovery
of ancient asteroid-battered organisms differed from charcoal associated
with normal wildfires, which was the team's leading hypothesis for a while.
Charcoal formed by impact instead of wildfire, she added, is "much more
homogeneous and points to a lower temperature of formation."
She said the impact charcoal found in the craters was similar, but not
identical, to charcoal that is formed when wood is intermixed with
pyroclastic flows. (Pyroclastic flows form from erupting volcanoes.)
The smaller impact craters Losiak studies — those that are only up to 656
feet (200 meters) in diameter — form every 200 years or so and thus present
numerous opportunities to study formation conditions, she said.
But her focus is distinct: "Most people are interested in gigantic
collisions because those are capable of causing planet-scale damage — the
diminishment of dinosaurs is the best, and so far the only, example of this
kind of event," she said, referring to the asteroid event that led to the
extinction of the non-avian dinosaurs 66 million years ago.
Losiak first came across the mysterious charcoal near a small impact crater
in Estonia. She began work during a summer school opportunity as a newly
minted Ph.D. and then returned a year later to lead a project to uncover and
study the "paleosoil." Paleosoil, she said, is an ancient soil covered by
the material removed from the crater during its formation.
As it turned out, the team never found the paleosoil. But after three days
of digging by hand, a time-consuming necessity due to environmental
protection, her team found charcoal.
"At first, we thought this charcoal was formed by wildfires that occurred
shortly before the impact, and charcoal just got tangled in this
extraterrestrial situation," she said. "But later, I found similar charcoal
in other impact craters, and started to think that something was not right
with this hypothesis."
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 far away from each other, and across a
timespan of thousands of years.
'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 charcoal," she said. That's when the
team uncovered that wildfires were not involved at all.
NASA and other entities are continually on the hunt for extraterrestrial
bodies, like comets or asteroids, that may cause a crater on Earth's
surface. So far, scientists have found no impending hazards to worry about.
But Losiak said proper disaster preparedness will benefit from studies such
as hers.
"This study improves our understanding of environmental effects of small
impact crater formation," she said. For incoming impactors, she added, "we
will be able to more precisely determine the size and type of evacuation
zone necessary."
Relatively large impact events do crop up recently in recorded history. One
of the most famous examples is the Tunguska event, which flattened roughly
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 due to glass and other debris,
but otherwise, the damage was minimal.
Losiak and her team plan to go to another set of small impact craters in
Argentina, in a region called Campo del Cielo, in late September to follow
up on the research.
"We will collect more data, and samples, and hopefully we will be able to
find more organisms killed by the asteroids," Losiak said. "Campo del Cielo
is particularly interesting because there are not only true impact craters —
sites where an asteroid literally exploded when it touched the ground — but
also penetration funnels."
A penetration funnel occurs when an asteroid slows down in the atmosphere
during its entry to Earth. This formation happens when it is hitting the
ground with velocity 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 the funnels in the same area, she added.
A study based on the research was published Aug. 31 in the journal Geology
Reference:
A. Losiak, C.M. Belcher, J. Plado, A. Jõeleht, C.D.K. Herd, R.S. Kofman, M.
Szokaluk, W. Szczuciński, A. Muszyński, E.M. Wild, S.J. Baker; Small impact
cratering processes produce distinctive charcoal assemblages. Geology 2022;
DOI: 10.1130/G50056.1
Tags:
Space & Astrophysics