March 2018^ DISCOVER^11MICROSTOCKER2/123RF
THE TRANSANTARCTIC MOUNTAINS SPLIT
our planet’s southernmost continent
into east and west, at times rising more
than 14,000 feet high. Today, it’s a
barren landscape of inhospitable rock
and ice. But for the scientists who hike
and camp this rocky spine, it’s also a
portal to another Earth.
Park University paleobotanist
Patty Ryberg and her colleagues are
uncovering the fossilized remains of a
lush forest that thrived in the Antarctic
Circle some 260 million years ago
during the Permian period. One type
of tree, called glossopterids, dominated
much of a supercontinent. Then they
vanished in a geological instant.
The glossopterids didn’t die alone.
About 90 percent of life on Earth was
snuffed out in our planet’s biggest
known extinction, called the Great
Dying. What killed everything?
Scientists have long debated the
causes of this event and Earth’s four
other major extinctions, usually
pointing to various volcanoes or
asteroids. But it’s tough to precisely date
rocks that old, so connecting a mass
extinction with one particular impact or
eruption is often controversial.
Now, a global campaign to map
Earth’s ancient mega-eruptions,
paired with advances in rock dating,
is pushing us closer than ever to
explaining why some volcanoes
and asteroids kill and others don’t.
Those results show that the size of an
eruption or asteroid isn’t as important
as the type of rocks incinerated.
One suspect behind several mass
extinctions is a kind of enormous
volcanic zone called a large igneous
province, or LIP. Picture a flattish,
layer cake-like volcano big enoughto cover a country — or a continent.
Amid the seemingly endless oozing
lava, its internal plumbing system rips
open miles-deep cracks like something
from a bombastic action flick.
Every major extinction coincides
with one of these eruptions. An LIP
called the Siberian Traps formed
just as the ancient forests Ryberg
studies disappeared in Antarctica.
Some 50 million years later, an LIP
called the Central Atlantic
Magmatic Province coincided
with another mass extinction
— one that eventually led
to the rise of the dinosaurs.
But while those eruptions
lasted for perhaps a million
years, the extinctions
happened in much shorter
time periods. Why?
Carleton University
geoscientist Richard Ernst,
who has studied LIPs for
two decades, launched a
large-scale effort in 2010
to find answers. Although
ancient LIPs are now
eroded and often hard to spot, Ernst
found he could map the behemoths
by examining their ancient magma
plumbing systems.
His results were surprising: 20
previously undiscovered LIPs, all over
the world. Incredibly, many formed
billions of years ago and left no signs
of a mass extinction. By using high-
tech dating techniques to examine
crystals in the rock, Ernst’s team has
also narrowed down the timelines of
these eruptions.
“Once we were able to start dating
them — and to date them very
precisely — then it was just stunning,”A Killer Connection?
BIG IDEANew research ties mass extinctions to the rocks beneath our feet.
Ernst says. His team and others can
now pinpoint LIPs to within 100,
years of their eruptions.
These new discoveries also help
explain what was happening at
LIPs during mass extinctions. For
example, as the Siberian Traps
formed, huge ponds of lava pooled
deep underground. This magma
cooked surrounding sedimentary
rocks as well as enormous seams of
coal. As they burned, those organic
matter-rich rocks released gases like
sulfur and carbon dioxide. Once the
pressure below was too much, miles-
deep cracks ripped open on Earth’s
surface, freeing the greenhouse gases.
Our planetary thermostat likely rose
dozens of degrees Fahrenheit. These
same organics were burned and
released in eruptions that wiped out
Triassic life and gave rise
to the dinosaurs, according
to a Nature study last May.
“It’s a very short period
of time for this to build
up and have such a kill
mechanism for a lot of
life on the planet,” Ernst
says. “These things have a
wicked climatic effect.”
The type of rocks
burned isn’t just important
for mega-eruptions. A
recent drilling expedition
to Mexico’s dino-killing
Chicxulub crater — the
only mass extinction
conclusively linked to an impact —
found the asteroid hit sedimentary
rock rich in sulfurs. And a November
Nature study showed such rocks
cover just 13 percent of Earth’s
surface. The dinosaurs might’ve
survived if the space rock hit
elsewhere.
So, really, mass extinctions often
just boil down to bad luck.
“My lesson from this is that the
Earth can go through dramatic
changes,” Ernst says. “The planet
doesn’t particularly care about the
biology on it, including humans.”
ERIC BETZAbout 90
percent of life
on Earth was
snuffed out
in our planet’s
biggest
known
extinction,
called the
Great Dying.