Sky & Telescope - October 2021 - 24

Planetary Calamity, Part II
500 microns
500 microns
FORAMINIFERA Before the K-Pg extinction event, deep-sea foram fossil specimens are large and diverse (left). But after the extinction, large
forams disappear (right, note same scale). Abrupt environmental changes favor smaller organisms, which have more rapid life cycles and need fewer
resources than larger organisms.
they've made their reputation on this - and
nobody can possibly admit that they might be
wrong, " Keller says. " It's totally non-scientific. "
And yet others would say the same about
Keller. " She's made a career of being a contrarian, "
Norris says. " I think that her science is
just driven by this idea that the impact was not
the cause, and she sort of hunts around for
evidence for that. "
But Grasby, a leading expert on mercury
who was not a coauthor on Keller's recent
paper, was quite impressed by her latest work,
arguing that the analysis is solid. In addition,
it matches findings from the other major mass
extinctions, which is promising - especially if
you abide by Occam's razor, the philosophical
idea that the simplest explanation is often the
correct one.
Grasby is also grateful for the contrarian
view. " I just appreciate that Gerta [Keller] is
33
BILLION TONS
CO2 emitted by
energy-related human
activities in 2019
400
BILLION TONS
Estimated O2 released
instantaneously by
Chicxulub impact
3,000-22,000
BILLION TONS
Estimated total
CO2 released by
Deccan Traps, over
several hundred
thousand years
working hard to keep the debate going, and I
think it's good for science to see some healthy
active debate on these things, " he says. " So
it's good for her to be so doggedly pressing the
cause. "
Indeed, many agree that the debate fuels
progress, pushing experts to dig deeper -
both literally and figuratively. And that is
crucial if scientists want to avoid another
global catastrophe.
The Chicxulub impact, for example, is
sometimes upheld as the reason why we
need to scour the skies in search of other
life-threatening meteoroids. Although Keller
argues that justification is overblown, there is
no question that Chicxulub certainly wreaked
havoc on the local ecosystem. " It is a preventable
natural disaster, if you go look, " says Amy
Mainzer (University of Arizona). And NASA
is looking. The Center for Near Earth Object
MASS EXTINCTION EVENTS
Five major extinction events appear
in Earth's fossil record. Some, like
the Permian extinction (also known
as " The Great Dying " ), are clearly
tied to volcanic eruptions; others'
causes are still debated. There are
dozens more smaller extinction
events in the geologic record.
FRACTION
OF SPECIES
ELIMINATED
FRACTION
OF SPECIES
ELIMINATED
TRILOBITES
85%
GRAPTOLITES
Time Frame
(million years
ago, approx.)
Suspected
Causes
24 OCTOBER 2021 * SKY & TELESCOPE
500
444
End-Ordovician
Global cooling
and glaciation
400
372 359
Late Devonian
(multiple events)
Low oxygen levels in
oceans, causes unclear
70-80%
300
FORAMS: SCRIPPS INSTITUTION OF OCEANOGRAPHY / UNIV. OF
CALIFORNIA, SAN DIEGO (2); TIMELINE: TERRI DUBÉ / S&T; GRAPTOLITES:
LILIYA BUTENKO / SHUTTERSTOCK; TRILOBITES: MORPHART CREATION /
SHUTTERSTOCK

Sky & Telescope - October 2021

Table of Contents for the Digital Edition of Sky & Telescope - October 2021

Contents
Sky & Telescope - October 2021 - Cover1
Sky & Telescope - October 2021 - Cover2
Sky & Telescope - October 2021 - 1
Sky & Telescope - October 2021 - Contents
Sky & Telescope - October 2021 - 3
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