Sky & Telescope - January 2022 - 6

LIP COMMISSION MAP, UPDATED FROM R. E. ERNST AND N. YOUBI /
PALAEOGEOGRAPHY, PALAEOCLIMATOLOGY, PALAEOECOLOGY 2017
FROM OUR READERS
180°
120°W
60°W
0°
60°E
120°E
180°
60°N
30°N
0°
30°S
60°S
Mass Extinction Events
I'm an amateur astronomer and an amateur volcanologist. Over the years, I've
come to the conclusion that the discussion over the trigger of mass extinctions
like the one in Shannon Hall's article " The Case of the Dead Dinosaurs " (S&T:
Oct. 2021, p. 18) is not about what individual process caused them. Rather,
the question is what combination of insults to the biosphere caused a mass
extinction. We have to be careful about pointing fingers as the number of
known mass extinctions is relatively small, only showing up with multicellular
life and fossils present in, say, the last half billion years.
There is an outfit that calls itself the Large Igneous Provinces Commission
(largeigneousprovinces.org). It maintains a database of massive volcanic
eruptions, known as large igneous provinces (LIPs), stretching back nearly
3.5 billion years.
One logical conclusion would be that life on this planet evolved in the
presence of LIP formations and is reasonably tolerant of them. The creation of
every LIP formation does not coincide with a mass extinction, but every mass
extinction seems to have a major volcanic eruption somewhere near in time.
What if a combination of massive environmental " insults " is what pushes
the biosphere into a mass extinction event? For example, we know that the
most recent mass extinction, roughly 65 million years ago, took place close to
two events: a huge asteroid impact on the coast of what is now the Yucatán
Peninsula, closely preceded by the enormous Deccan Traps eruptions in what is
now central India.
Another approach would be to look at two known major insults that happened
around the same time and try to figure out why a mass extinction event
did not happen. A good example would be the end of the Eocene Epoch, when
there was only a minor extinction event. At the time, three LIPs were in play:
one in the Afar region of Ethiopia, and two poorly dated events in western and
central Europe and in northern and central Africa. There were also multiple
impact events around the same time - Popigai, Chesapeake Bay, and Toms
Canyon. While there was a minor extinction event, it was not a major one,
even though the planet cooled overall.
Perspective is everything. We may very well find that these events are not
an either-or game. The investigation into them will be fascinating.
Alex Gimarc * Anchorage, Alaska
pThe results of dozens of ample magma flows, known as large igneous provinces, cover the
Earth. This map contains those from the past billion years, some of which scientists have linked
to mass extinction events.
6
JANUARY 2022 * SKY & TELESCOPE
A Prehistoric Cold Case
Shannon Hall's article was much
appreciated. If you pick up a globe of
Earth, the Chicxulub impact site and the
Deccan Traps are not quite antipodal
but seemingly would have been more so
65 million years ago before the Indian
continent drifted so far north. This has
always seemed like an unlikely coincidence
to me. The extreme violence of
the impact would have been seismically
concentrated at the antipode. So Paul
Renne and Courtney Sprain's conjecture
about the impact having " kicked the
ongoing volcanism into high gear " seems
to be the more likely scenario. Given the
difficulty of dating past events accurately,
perhaps the impact was even more
causal in producing the Deccan Traps'
enormous basalt flows.
Marcus Honnecke
North Park, Colorado
Shannon Hall presented a zesty debate
on the mass extinction of the dinosaurs.
Was it caused by an impact or a
volcano? Both, I think. Representations
of the shock wave propagating from the
impact site often show an expanding
ring of destruction that diminishes in
strength as it widens. Halfway around
the world, the ring begins to contract
and intensifies in energy as it races to
a focus point on the opposite side of
Earth from the Chicxulub impact. However,
it isn't a sharp focus because shock
waves pass through each of the many
geographic formations on Earth differently
due to their varying densities.
The Deccan Traps had been pouring
out lava for hundreds of thousands of
years before the asteroid hit, but the
propagated impact energy would have
blown the volcanic vent wide open.
This accounts for the fossil evidence,
which shows earlier extinction events of
varying severity around the globe and
a massive spike in extinctions near the
time of the impact.
David L. Koren
Sarver, Pennsylvania
Sabrina Garvin replies: You both
make good points. The theory that
the massive lava flows at the Deccan Traps
"
http://www.largeigneousprovinces.org

Sky & Telescope - January 2022

Table of Contents for the Digital Edition of Sky & Telescope - January 2022

Contents
Sky & Telescope - January 2022 - Cover1
Sky & Telescope - January 2022 - Cover2
Sky & Telescope - January 2022 - 1
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Sky & Telescope - January 2022 - Cover3
Sky & Telescope - January 2022 - Cover4
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