Death from Space
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.
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
Contact: 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.
Contact: 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
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