My
friend Margo has been saying that she thinks the methane is coming,
not just from melting permafrost but from magma.
There
seemed to be no known scientific basis for such a contention –
until I read this.
Underground
magma triggered Earth’s worst mass extinction with greenhouse gases
There
are parallels between today’s and past greenhouse gas-driven
climate changes
Howard
Lee
1
August, 2017
Coincidence
doesn’t prove causality, as they say, but when the same two things
happen together over and over again through the vast span of
geological time, there must be a causal link. Of some 18 major and
minor mass extinctions since the dawn of complex life, most
happened at the same time as
a rare, epic volcanic phenomenon called a Large Igneous Province
(LIP). Many
of those extinctions were
also accompanied by abrupt climate warming, expansion of ocean dead
zones and acidification, like today.
Earth’s
most severe mass extinction, the “Great Dying,” began 251.94
million years ago at the end of the Permian period, with the loss
of more
than 90% of
marine species. Precise rock dates published in 2014 and 2015 proved
that the extinction coincided with the Siberian Traps LIP, an epic
outpouring of lava and intrusions of underground magma covering an
area of northern Asia the size of Europe.
But
those rock dates presented science with a new puzzle: why was the
mass extinction event much shorter than the eruptions? And why did
the extinction happen some 300,000 years after the lava began to
flow?
It’s
clearly not the entirety of the LIP that’s guilty. There’s a
subinterval that’s doing the work, and I set out to figure out
which subinterval that was, and what makes it special.
Burgess
noticed that the beginning of the mass extinction, as well as a jolt
to the carbon cycle and abrupt climate warming, coincided exactly
with a switch in the style of volcanic activity in the Siberian
Traps. During the initial 300,000 years of the eruptions, basalt lava
poured over a vast area of Siberia building to several kilometers
thick. In this time there was some stress to life in the Northern
Hemisphere, but no mass extinction. Life only began to disappear
across the globe at exactly the same time that lava stopped erupting
above ground, and instead began to inject as sheets of magma
underground.
In
Siberia you have got the Tunguska Basin which is a thick package of
sediments that contain carbon-bearing rocks like limestone and coal.
When you start intruding magma, [it] cooks those sediments and
liberates the volatiles. So the deadly interval of magma in the
entire Large Igneous Province is the first material to intrude and
pond into the shallow crust
In
other words, it wasn’t the lava, it was the underground magma that
started the killing, by releasing greenhouse gases.
Norwegian
scientist Henrik Svensen had earlier identified hundreds
of unusual volcanic vents called
“diatreme pipes” all over Siberia that connected underground
intrusions of magma (“sills”) to the atmosphere, showing signs of
violent gas explosions. This new work emphasizes the importance of
Svensen’s 2009 conclusions:
The
diatremes that have been mapped are the geologic representation of
that gas escape on a catastrophic level. Our hypothesis is that the
first sills to be intruded are the ones that really do the killing
[by] large scale gas escape likely via these diatremes.
Svensen,
who was not involved in Burgess’ study, commented:
The
Burgess et al paper is a crucial step towards a new understanding of
the role of volcanism in driving extinctions. It’s not the
spectacular volcanic eruptions that we should pay attention too -
it’s their quiet relative, the sub-volcanic network of intrusions,
that did the job. The new study shows convincingly that we are on the
right track.
Greenhouse
gas as a killer
While
other scientists have proposed that an array of killers may have been
involved in the end-Permian mass extinction, from mercury poisoning
to ultraviolet rays and ozone collapse to acid rain, Burgess argues
that it was principally greenhouse gas emissions triggered by magma
intrusions that caused the extinction through abrupt global warming
and ocean acidification. I asked him to outline the evidence for
that.
There
are 3 primary lines of evidence that support that link. The first is:
right before the onset of the mass extinction we have evidence for a
massive input of isotopically light carbon into the marine system.
He
went on to explain various lines of evidence that point to the source
of that carbon being methane and carbon dioxide resulting from magma
intruding and cooking organic-rich sediments. He continued:
Just
prior to extinction and persisting after the mass extinction the sea
surface temperature is thought to have gone up about 10°C. You get
that increase by pumping greenhouse gas into the atmosphere. So
that’s the second.
And
then the third line of evidence is a physiologic selectivity to the
marine mass extinction. Organisms that make their shells out of
calcium carbonate suffer much higher mortality than organisms that
make their shells out of silica, for example, which suggests that the
ocean was acidified, and you get that by pumping gases like CO2 into
the atmosphere.
That’s
not to say that other factors had no role in ruining the environment:
There
is a cacophony of kill mechanisms, and I think that this first pulse
of sills is the trigger for quite a few of those, sitting at the top,
and beneath it are a cascade of negative effects from ocean
acidification to climate warming and on down the line.
A
series of associated events
Coincidentally,
Joshua Davies of the University of Geneva and colleagues have just
narrowed down the trigger for the end-Triassic mass extinction,
another of Earth’s biggest mass extinctions, to
the underground phase of its associated Large Igneous Province.
The Central Atlantic Magmatic Province (CAMP) is another enormous
igneous province which stretches from Maine to South America, and
includes the Palisade Sill visible from Manhattan.
They
too used high precision rock dates on a vast sill that intruded
organic rich sediments in the Amazon Basin, and found that this
underground magma intrusion also coincided with the extinction. Like
Burgess, Davies also argues that greenhouse gas baked from sediments
drove climate change, which drove the mass extinction in a smaller
repeat of the end-Permian events, this time 201.5 million years ago.
“I
think CAMP is very similar to the Siberian Traps and that’s the
reason why there’s an extinction at that time. I’m not surprised
that they got similar results,” said Burgess.
Diatreme
pipes from
magma intrusions have also been identified as a likely cause for a
more recent global warming and very minor extinction event – the
Paleocene–Eocene Thermal Maximum (PETM) 56 million years ago.
Again, prodigious quantities of greenhouse gases erupted
from oil-rich deposits,
although in that case it’s been hard to locate and date the
“smoking gun” intrusions due to the fact that they are under the
Atlantic Ocean.
A
predictive model
Burgess’
insight makes a testable prediction:
Only
Large Igneous Provinces characterized by sills intruded into a
volatile-fertile basin are going to be lethal on a global scale.
This
may explain why some Large Igneous Provinces are tied to mass
extinctions, and some are not. Burgess thinks that the Deccan LIP,
which happened at the time when the dinosaurs disappeared at the end
of the Cretaceous, would not have triggered a major mass extinction
on its own:
The
Deccan Traps doesn’t satisfy those 2 criteria. It’s predominantly
flood basalt lavas erupted onto old granitic rock. Acting alone there
would likely have been negative effects on the biosphere because of
the gases and the particulate matter released by those lavas, which
are not insignificant, but I would argue that acting alone it would
have been minor relative to the observed mass extinction. But with
the Chicxulub impactor sharing the causal burden together they caused
the mass extinction at the end of the Cretaceous.
Parallels
today?
The
more science learns of these past greenhouse gas-driven events, the
more uncomfortable the parallels to today become. I asked Burgess if
it was ridiculous to make the comparison.
No,
I don’t think the comparison is ridiculous at all, and I think that
the timescales over which the environment changes associated with
mass extinctions are frighteningly similar to the timescales over
which our current climate is changing. The cause might be different
but the hallmarks are similar.
Geologically
fast build-up of greenhouse gas linked to warming, rising sea-levels,
widespread oxygen-starved ocean dead zones and ocean acidification
are fairly
consistent across
the mass extinction events, and those same symptoms are happening
today as a result of human-driven climate change.
The
Anthropocene will more likely resemble the end-Permian and
end-Cretaceous disasters, rather than the PETM.
When
the promises made for the 2016 Paris Agreement on climate change are
added up, they aim to limit peak warming this century to
about 3.3ºCcompared
to about 4.2ºC for the business-as-usual scenario, and the 2ºC
limit the world is aiming to stay under. It’s sobering to compare
those numbers to the majority of mass extinctions in the geological
record which were characterized by abrupt warmings typically
around 6-7ºC.
Howard
Lee is a geologist and science writer who focuses on past climate
changes.
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