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this program possible.

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Support your local PBS station.

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All right.
There's a really
good site right here.

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We can take a look
at this boundary layer.

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All right. So we're just
a little bit outside

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of downtown
Salt Lake City,

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{\an8}and we're
on this trail.

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{\an8}Why are we here?

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{\an8}What are we
looking at?

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{\an8}Well, this layer here

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{\an8}represents the worst
mass extinction

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{\an8}that ever happened
on Earth.

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These rocks were deposited

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during the Great Dying
252 million years ago.

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Gabriel-Philip Santos: It might
not look like much,

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but this geologic boundary marks
the single greatest catastrophe

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that life on Earth ever faced.

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On one side of the boundary
are rock layers

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from the late Permian Period,

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the final chapter
of the Paleozoic,

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the era of ancient life,

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and on the other side
of the boundary

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are rock layers from
the Early Triassic Period,

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the first chapter
of the Mesozoic,

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the fossil record's
middle era.

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Kallie Moore: An apocalypse
occurred at this boundary

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between the Permian and Triassic
that wiped out

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more than 80% of all species,
altering the course

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of evolution in ways
that we're still feeling

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the effects of today
252 million years later.

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{\an8}So even though the transition
from the Late Permian

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{\an8}to the Early Triassic
represents only

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{\an8}a brief moment in geologic time,

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crossing the boundary
feels like traveling

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to an entirely different,
much bleaker world.

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Michelle Barboza-Ramirez:
The Late Permian's
flourishing ecosystems

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teeming with diverse species
suddenly vanish

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{\an8}almost entirely
from the fossil record,

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{\an8}and in the desolation
of the Early Triassic

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{\an8}that follows,
all that remains are just

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{\an8}a few surviving branches
of a tree of life

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{\an8}that has otherwise
withered away.

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Blake de Pastino: The fossil
record of this time tells

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the story of a cataclysm
that paleontologists

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call "The Great Dying,"
the closest

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that complex life
on Earth ever came

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to total annihilation
and an event that

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our ancient relatives
barely survived.

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{\an8}It was a complex event involving

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{\an8}a geologic, climatic,
and ecological cascade

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{\an8}that is still being pieced
together by scientists

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reading the rocks
at places like this,

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at the literal end of an era.

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Benjamin Burger: These rocks
are 252 million years old,

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so they're like
a little time capsule.

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But what we can say is
that the Great Dying was

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set in motion by a force
deep within the planet itself

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under the northern reaches
of Pangea

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thousands of kilometers
away from here

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in what's now Siberia.

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{\an8}If things had gone
just a little differently

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{\an8}at that thin boundary
for our direct ancestors,

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if they had been just
a little less scrappy

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and a little less lucky,

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they could have easily joined
the majority

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of animal life on Earth
and succumbed

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to the worst ever
mass extinction.

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The biodiversity
of planet Earth is balanced

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by two opposing forces--

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the origin of species,
speciation;

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and the loss
of species, extinction--

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both of which happen constantly
in the ecological background.

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The concept that species
come and go might seem

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pretty obvious,
seeing as many of us grew up

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learning about
the long-gone days of mammoths,

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dinosaurs, and dodos

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or the numerous species
facing extinction today,

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but in reality, the idea
that species can vanish

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entirely from the face
of the Earth is actually

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a relatively recent one.

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The concept
of extinction only became

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established in Western science
at the turn of the 19th century,

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most notably by a French
naturalist named Georges Cuvier,

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sometimes known as
the Father of Paleontology.

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Before Cuvier,
the prevailing European view

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of the natural world was
a much more static one,

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rooted in Christian theology--

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life on Earth was
perfect and unchanging.

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The species of today
had existed since the start

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and would always exist.

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They had been made deliberately
by a Creator,

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and He wouldn't
allow them to be unmade.

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The idea of a species
dying out completely--

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removed like a chess piece
from the board of creation--

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was so outlandish
that it wasn't even

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seriously entertained by most
pre-19th century thinkers,

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and even when the remains
of strange ancient creatures

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were found, it was assumed
that living members

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of these species

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still existed
somewhere in the world,

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including by Thomas Jefferson,

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who had a personal fascination
with fossils

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and believed that
species like mammoths

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and giant sloths would
likely be found living

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somewhere in the American West,

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{\an8}but Cuvier argued
that the fossil record

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{\an8}contained the bones
of species clearly distinct

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{\an8}from living ones
and that, in many cases,

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{\an8}they were just too big
to have stayed hidden.

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{\an8}These were animals that
were not alive anymore

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from a time when
planet Earth must have been

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a wildly different place
than it is now.

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Cuvier's concept
of extinction was

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a revolution
in the way that we saw

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the natural world.

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It was no longer stable
and unchanging.

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This was a world in flux,

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and it had a dramatic
and mysterious history.

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Over the more than
200 years of studying

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the fossil record
since Cuvier's time,

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our understanding
of that history--

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and just how profoundly it has
been shaped by extinction--

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has only become more radical

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because now we know
that not only can species

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go extinct but that,

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on at least 5 separate occasions
in the history

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of complex life,
most species suddenly did.

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The most famous
of the Big 5 by far is also

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the most recent of them,
the End-Cretaceous Extinction

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at the close of the Mesozoic Era
some 66 million years ago.

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You probably know it
as the time that

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a gigantic asteroid impact

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ended the reign
of the dinosaurs,

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but despite it being
the most well-known

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mass extinction event,
as well as the most sudden

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and dramatic,

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it wasn't actually
the worst one.

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That honor goes to
the Great Dying at the end

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of the Permian Period,

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when our planet suffered
a level of death

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that it had never seen before

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and thankfully
has never seen since.

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In our journey through
the Permian so far,

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we've watched ecosystems
get increasingly

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impressive, dynamic,
and layered,

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but just like a house of cards,
the more complex

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and multi-dimensional
an ecosystem gets,

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the more dramatic
its collapse will be,

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and unlike the End-Cretaceous
asteroid impact,

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the Great Dying wasn't caused
by an external threat

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descending from above

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but by an internal threat
rising from below.

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Some of my colleagues
on "Eons" described

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the Great Dying

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as the "Murder
on the Orient Express"

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of mass extinctions.

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Like, everyone did it.

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Mm-hmm. Mm-hmm.

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Every ecological factor
on that train tried

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to kill life on Earth.

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Mm-hmm.

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There were a lot
of variables there.

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{\an8}So can you walk me
through everything

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{\an8}that was going on
that triggered

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{\an8}the Great Dying?

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{\an8}Yeah, there were,
of course,

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many culprits
in this extinction event,

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but there was
a main trigger,

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and that was
the eruption

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of a large amount
of lava in what is

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now Russia called
the Siberian Traps.

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Around
252 million years ago,

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deep within the Earth,
a superheated plume

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of molten rock formed inside
the planet's mantle layer.

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As convection currents
carried it higher and higher,

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this plume pushed against
and melted

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the planet's crust
until eventually

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it broke through entirely
in northern Pangea

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in what would
one day be Siberia,

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triggering some of the largest
volcanic eruptions in history.

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Pia Viglietti: So we're talking
about an area the size

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of Western Europe
over 2,000 feet tall.

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This happened over the course
of a million years.

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This put tons and tons
of carbon dioxide

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into the atmosphere
and other greenhouse gases.

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The consequences
of these eruptions

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were felt on every inch
of the supercontinent of Pangea

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and even the depths
of the oceans

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that surrounded it

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because these eruptions
did much more

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than just spew out
an obscene amount of lava.

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They also set off
a chain reaction that turned

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this regional disaster
into a global crisis

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00:09:02,809 --> 00:09:04,710
of unprecedented proportions.

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See, what made the eruptions
so especially devastating

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was their location.

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That eruption was
situated

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underneath a huge basin
of carboniferous coal.

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Permian Siberia
contained vast

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00:09:18,425 --> 00:09:20,459
fossil fuel deposits
that had formed

201
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in the extensive tropical swamps
of the Carboniferous Period

202
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right before the Permian began.

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As its name suggests,
the Carboniferous is

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famous for being the enormous
amount of carbon dioxide that

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was pulled from the atmosphere
by its plants.

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As these plants died
and fell into the murky depths

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of the swamps,
they didn't decompose

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but became buried
and compressed underground,

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locking away all that
carbon in a solid form,

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00:09:45,252 --> 00:09:47,520
over a trillion tons of coal.

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Millions of years
later at the end

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of the Permian,
when these ancient coal deposits

213
00:09:51,725 --> 00:09:54,460
came into contact
with red hot molten rock

214
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from the End-Permian eruptions,
they ignited,

215
00:09:57,464 --> 00:09:59,999
and once they were on fire,
no force on Earth

216
00:10:00,000 --> 00:10:01,500
could put them out.

217
00:10:01,501 --> 00:10:03,402
Now, one of the most
painful lessons

218
00:10:03,403 --> 00:10:06,205
that our species has learned
over the last century is that

219
00:10:06,206 --> 00:10:09,041
when you burn a lot
of coal really fast,

220
00:10:09,042 --> 00:10:11,877
the planetary effects
are pretty dire.

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Suddenly, releasing all
that stored carbon back

222
00:10:14,481 --> 00:10:16,415
into the atmosphere
triggers rapid

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00:10:16,416 --> 00:10:18,250
and intense global warming,

224
00:10:18,251 --> 00:10:22,321
and 252 million years ago,
this same process set in.

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{\an8}The combination
of emissions released

226
00:10:24,291 --> 00:10:25,758
{\an8}directly from the eruptions,

227
00:10:25,759 --> 00:10:27,493
{\an8}as well as from the unchecked
coal combustion,

228
00:10:27,494 --> 00:10:30,563
{\an8}raised atmospheric carbon
dioxide levels 6-fold

229
00:10:30,564 --> 00:10:32,298
{\an8}according to some estimates.

230
00:10:32,299 --> 00:10:34,100
{\an8}Now, if that was
a little bit higher,

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00:10:34,101 --> 00:10:39,772
it would be lethal
to all air-breathing
terrestrial animals.

232
00:10:39,773 --> 00:10:41,874
{\an8}The runaway
greenhouse effect that followed

233
00:10:41,875 --> 00:10:43,442
{\an8}was intense, increasing

234
00:10:43,443 --> 00:10:45,011
{\an8}ambient temperatures to around

235
00:10:45,012 --> 00:10:46,879
{\an8}35-40 degrees Celsius--

236
00:10:46,880 --> 00:10:48,347
{\an8}beyond the ability of most

237
00:10:48,348 --> 00:10:50,316
{\an8}ecosystems to tolerate for long.

238
00:10:50,317 --> 00:10:51,751
{\an8}We also see evidence

239
00:10:51,752 --> 00:10:53,219
{\an8}of dead zones where

240
00:10:53,220 --> 00:10:55,221
rising temperatures
just made parts

241
00:10:55,222 --> 00:10:56,756
of the globe
inhospitable

242
00:10:56,757 --> 00:10:59,358
for all life,
particularly
at the equators.

243
00:10:59,359 --> 00:11:00,960
Plus,
the massive volcanism

244
00:11:00,961 --> 00:11:03,796
and coal combustion also spewed
out other pollutants,

245
00:11:03,797 --> 00:11:06,432
like sulfur dioxide,
triggering planet-wide

246
00:11:06,433 --> 00:11:09,635
acid rain with a pH level
equivalent to vinegar.

247
00:11:09,636 --> 00:11:11,971
The Great Dying literally
burned the world,

248
00:11:11,972 --> 00:11:15,842
and from the seas to the trees,
no ecosystem was safe.

249
00:11:22,282 --> 00:11:24,683
So globally,
what we saw on land,

250
00:11:24,684 --> 00:11:27,553
this triggered a number
of extreme climatic events

251
00:11:27,554 --> 00:11:31,557
like mega storms,
flooding, droughts, wildfires.

252
00:11:31,558 --> 00:11:33,559
In the oceans,
rising temperatures

253
00:11:33,560 --> 00:11:36,529
caused ocean acidification
and anoxia,

254
00:11:36,530 --> 00:11:39,198
which means the oceans
lose their oxygen.

255
00:11:39,199 --> 00:11:41,667
The ocean extinction
was truly devastating.

256
00:11:41,668 --> 00:11:44,236
It's believed that
8 out of every 10

257
00:11:44,237 --> 00:11:46,072
marine species
went extinct.

258
00:11:46,073 --> 00:11:48,674
Some of the oldest features of
the ancient world's marine life

259
00:11:48,675 --> 00:11:51,110
vanished forever,
like trilobites

260
00:11:51,111 --> 00:11:52,812
and horn corals, for example.

261
00:11:52,813 --> 00:11:54,580
These groups had lived
in the oceans

262
00:11:54,581 --> 00:11:56,682
of planet Earth for hundreds
of millions of years,

263
00:11:56,683 --> 00:11:58,717
some of them dating all
the way back

264
00:11:58,718 --> 00:12:00,853
to the Cambrian period when
complex animal life

265
00:12:00,854 --> 00:12:02,188
first became common.

266
00:12:02,189 --> 00:12:03,756
{\an8}Oh, my goodness.

267
00:12:05,525 --> 00:12:07,526
{\an8}Probably my
favorite invert.

268
00:12:07,527 --> 00:12:09,829
{\an8}Trilobites.
Oh, my God.

269
00:12:09,830 --> 00:12:11,530
They're just beautiful.
Look at these.

270
00:12:11,531 --> 00:12:13,165
So the specimens
in this drawer

271
00:12:13,166 --> 00:12:14,867
are trilobites
from the Cambrian Period

272
00:12:14,868 --> 00:12:16,235
of Earth history.
OK.

273
00:12:16,236 --> 00:12:17,670
I think they're around

274
00:12:17,671 --> 00:12:19,338
about 525 million years
old or so,

275
00:12:19,339 --> 00:12:20,706
and that's right around
the time when trilobites

276
00:12:20,707 --> 00:12:22,541
first show up
in the fossil record.

277
00:12:22,542 --> 00:12:24,443
They had lasted almost
the entire Paleozoic,

278
00:12:24,444 --> 00:12:26,378
facing every major
challenge that the world

279
00:12:26,379 --> 00:12:27,880
had thrown at them,

280
00:12:27,881 --> 00:12:30,316
including two of the Big 5
mass extinctions already,

281
00:12:30,317 --> 00:12:31,717
so it's a testament
to the severity

282
00:12:31,718 --> 00:12:33,486
of the Great Dying
that it finally proved

283
00:12:33,487 --> 00:12:36,822
a match for even these hardiest
of marine animals.

284
00:12:36,823 --> 00:12:38,524
What was
the last straw?

285
00:12:38,525 --> 00:12:39,992
Why couldn't
they make it

286
00:12:39,993 --> 00:12:41,494
through the Great Dying
if they'd made it

287
00:12:41,495 --> 00:12:42,761
through a quarter
billion years

288
00:12:42,762 --> 00:12:44,463
of other mass
extinction events?

289
00:12:44,464 --> 00:12:46,699
It's probably ultimately
in a way bad luck.

290
00:12:46,700 --> 00:12:48,501
Late Permian
trilobites are animals

291
00:12:48,502 --> 00:12:50,136
that mostly were living
in sort of

292
00:12:50,137 --> 00:12:51,537
shallow ocean environments,

293
00:12:51,538 --> 00:12:53,739
and those environments were
very strongly affected

294
00:12:53,740 --> 00:12:55,441
by all the bad things
that happen

295
00:12:55,442 --> 00:12:56,775
at the end
of the Permian.

296
00:12:56,776 --> 00:12:58,677
And even for groups
that made it

297
00:12:58,678 --> 00:13:00,713
through the extinction event,
most were whittled down

298
00:13:00,714 --> 00:13:03,048
to just a few lucky survivors.

299
00:13:03,049 --> 00:13:04,683
Take ammonoids, for example,

300
00:13:04,684 --> 00:13:07,386
the ancient shelled relatives
of squid and octopuses.

301
00:13:07,387 --> 00:13:09,021
They had been common
and diverse in the waters

302
00:13:09,022 --> 00:13:11,390
of the Permian
but experienced a bottleneck

303
00:13:11,391 --> 00:13:14,226
so severe that as few
as 3 lineages survived

304
00:13:14,227 --> 00:13:16,495
across the Permian-Triassic
boundary.

305
00:13:16,496 --> 00:13:18,797
Ammonoid history is
really a series

306
00:13:18,798 --> 00:13:20,933
of ups and downs,
waxings and wanings

307
00:13:20,934 --> 00:13:22,401
of their diversity.

308
00:13:22,402 --> 00:13:25,437
So there's several groups
of Paleozoic ammonoids

309
00:13:25,438 --> 00:13:29,074
that all go extinct
at the time of the Great Dying.

310
00:13:29,075 --> 00:13:31,143
However, one group
of ammonites,

311
00:13:31,144 --> 00:13:34,480
the Ceratitida, were doing
something different apparently

312
00:13:34,481 --> 00:13:36,081
and were sort of
on an upswing,

313
00:13:36,082 --> 00:13:38,517
and so they're the main
group of ammonites that

314
00:13:38,518 --> 00:13:40,519
survives into the Triassic,

315
00:13:40,520 --> 00:13:42,655
and it's essentially
animals like this then

316
00:13:42,656 --> 00:13:45,191
that are the progenitors
of all the rest

317
00:13:45,192 --> 00:13:46,525
of the Mesozoic ammonoids.

318
00:13:46,526 --> 00:13:48,260
Many other marine animal
groups passed

319
00:13:48,261 --> 00:13:49,662
through similar diversity
bottlenecks

320
00:13:49,663 --> 00:13:51,330
over the course
of the extinction event,

321
00:13:51,331 --> 00:13:53,332
from invertebrates
like reef-building sponges

322
00:13:53,333 --> 00:13:55,134
and corals to fishes

323
00:13:55,135 --> 00:13:57,570
In fact, for millions of years
after the extinction,

324
00:13:57,571 --> 00:14:00,372
not a single reef has been found
in the fossil record.

325
00:14:00,373 --> 00:14:02,374
It's the biggest so-called
reef gap

326
00:14:02,375 --> 00:14:04,276
in all of history
and a clear sign

327
00:14:04,277 --> 00:14:06,779
of a world
in ecological turmoil.

328
00:14:06,780 --> 00:14:09,415
Above the water line,
things were just as bad.

329
00:14:09,416 --> 00:14:13,152
We see just
a complete extinction

330
00:14:13,153 --> 00:14:16,288
of a lot of plants
that were living
at this time.

331
00:14:20,694 --> 00:14:22,328
Late Permian Pangea
was already

332
00:14:22,329 --> 00:14:25,698
hot and dry in many places
for part of the year at least,

333
00:14:25,699 --> 00:14:27,700
so the sudden
temperature spike was enough

334
00:14:27,701 --> 00:14:29,568
to push much
of the supercontinent

335
00:14:29,569 --> 00:14:31,870
into an almost
unsurvivable hellscape.

336
00:14:31,871 --> 00:14:34,440
Blistering temperatures,
drought, and acid rain

337
00:14:34,441 --> 00:14:36,709
triggered an ecological
collapse on land

338
00:14:36,710 --> 00:14:38,444
that took down the majority

339
00:14:38,445 --> 00:14:40,045
of all terrestrial species
with it,

340
00:14:40,046 --> 00:14:41,981
and it began
with the plants that formed

341
00:14:41,982 --> 00:14:44,316
the base of most
Permian food chains.

342
00:14:44,317 --> 00:14:46,185
Pangea's forests were
hit by periods

343
00:14:46,186 --> 00:14:48,954
of acid rain that
not only damaged their leaves

344
00:14:48,955 --> 00:14:50,856
and other tissues
but also upset

345
00:14:50,857 --> 00:14:52,658
the chemical balance
of the soil.

346
00:14:52,659 --> 00:14:55,461
Meanwhile, the runaway
greenhouse effect spiked

347
00:14:55,462 --> 00:14:57,630
temperatures by 10 degrees
Celsius,

348
00:14:57,631 --> 00:14:59,999
pushing all species outside
of the conditions

349
00:15:00,000 --> 00:15:01,367
they were adapted for.

350
00:15:01,368 --> 00:15:03,636
A lot of the plants
from the Carboniferous Period

351
00:15:03,637 --> 00:15:06,005
of time have a mechanism
of reproduction

352
00:15:06,006 --> 00:15:07,339
that requires water,

353
00:15:07,340 --> 00:15:10,542
things like ferns
and horsetails

354
00:15:10,543 --> 00:15:12,311
and those types of plants,

355
00:15:12,312 --> 00:15:15,180
so the loss of water,
freshwater

356
00:15:15,181 --> 00:15:17,816
that they could live in
really was devastating.

357
00:15:17,817 --> 00:15:19,818
We know from studies
of modern plants

358
00:15:19,819 --> 00:15:22,721
that at temperatures
of around 35-40 degrees Celsius

359
00:15:22,722 --> 00:15:25,291
the heat stress is often enough
for photosynthesis

360
00:15:25,292 --> 00:15:27,793
to slow down or even stop.

361
00:15:27,794 --> 00:15:30,329
In Australia and China,
increased charcoal

362
00:15:30,330 --> 00:15:31,897
in rock layers
dating to the time

363
00:15:31,898 --> 00:15:34,400
of the extinction
suggests that the heat,

364
00:15:34,401 --> 00:15:36,635
drought, and aridity
triggered a spike

365
00:15:36,636 --> 00:15:38,637
in wildfires
during the extinction, too,

366
00:15:38,638 --> 00:15:40,506
and for a while afterwards,

367
00:15:40,507 --> 00:15:42,341
we see the complete opposite.

368
00:15:42,342 --> 00:15:44,043
There's no charcoal at all.

369
00:15:44,044 --> 00:15:46,211
So it's crazy
what's happening.

370
00:15:46,212 --> 00:15:48,213
We have massive
forest fires

371
00:15:48,214 --> 00:15:50,049
that are occurring because
of the climate change.

372
00:15:50,050 --> 00:15:52,184
After that, we had
this period where there is

373
00:15:52,185 --> 00:15:53,752
no forests anymore.

374
00:15:53,753 --> 00:15:55,487
The vegetation
at that time was

375
00:15:55,488 --> 00:15:57,122
no higher than,
like, your knee,

376
00:15:57,123 --> 00:16:00,693
so all the forests,
all the trees were gone.

377
00:16:00,694 --> 00:16:02,861
The wildfires that tore
through forests

378
00:16:02,862 --> 00:16:05,064
during the Great Dying
would have further sped up

379
00:16:05,065 --> 00:16:07,099
the runaway greenhouse effect
by releasing

380
00:16:07,100 --> 00:16:10,002
even more carbon dioxide
into the atmosphere,

381
00:16:10,003 --> 00:16:12,705
and the loss of so much
vegetation meant that

382
00:16:12,706 --> 00:16:14,840
not only was there now
more carbon dioxide

383
00:16:14,841 --> 00:16:17,276
being emitted,
but there was also less capacity

384
00:16:17,277 --> 00:16:20,679
for natural carbon sinks
to draw that CO2 back down.

385
00:16:20,680 --> 00:16:22,514
It was a feedback loop
that only made

386
00:16:22,515 --> 00:16:25,017
the Great Dying even greater.

387
00:16:25,018 --> 00:16:26,785
Beyond scorching
temperatures,

388
00:16:26,786 --> 00:16:29,121
raging wildfires, and acid rain,

389
00:16:29,122 --> 00:16:31,757
there's also evidence that
a much less visible,

390
00:16:31,758 --> 00:16:33,892
but no less devastating,
factor may have led

391
00:16:33,893 --> 00:16:37,262
to the collapse
of Permian forests, radiation.

392
00:16:37,263 --> 00:16:39,965
{\an8}See, volcanic eruptions
also release gases

393
00:16:39,966 --> 00:16:41,667
{\an8}known for their ability
to deplete

394
00:16:41,668 --> 00:16:43,102
{\an8}the planet's ozone layer,

395
00:16:43,103 --> 00:16:44,837
{\an8}the protective shield
against the worst

396
00:16:44,838 --> 00:16:46,872
{\an8}of the sun's
ultraviolet radiation,

397
00:16:46,873 --> 00:16:49,742
{\an8}and the scale of
the Siberian Traps eruptions

398
00:16:49,743 --> 00:16:51,810
would have released
enough of these gases

399
00:16:51,811 --> 00:16:53,912
to severely weaken this shield,

400
00:16:53,913 --> 00:16:56,582
temporarily bathing
the surface of the planet

401
00:16:56,583 --> 00:16:59,451
in a dangerously
high level of UV exposure.

402
00:16:59,452 --> 00:17:01,153
And that
can be seen in some

403
00:17:01,154 --> 00:17:03,155
of these studies that have
looked at pollen

404
00:17:03,156 --> 00:17:05,124
through this zone,
and they noticed that

405
00:17:05,125 --> 00:17:06,859
there's a lot of mutations
in the pollen.

406
00:17:06,860 --> 00:17:08,594
It just doesn't
look healthy,

407
00:17:08,595 --> 00:17:10,462
and that's been
attributed to a lack

408
00:17:10,463 --> 00:17:12,164
of an ozone
during this period.

409
00:17:12,165 --> 00:17:13,899
This was yet
another mechanism that

410
00:17:13,900 --> 00:17:15,801
probably contributed
to the near-total

411
00:17:15,802 --> 00:17:18,504
global deforestation
at the end of the Permian,

412
00:17:18,505 --> 00:17:20,472
not by killing
the trees outright,

413
00:17:20,473 --> 00:17:22,474
but by affecting them
at the cellular

414
00:17:22,475 --> 00:17:24,576
and molecular level,
putting a hold

415
00:17:24,577 --> 00:17:27,045
on their ability to reproduce,

416
00:17:27,046 --> 00:17:29,014
but at least one group
seems to have flourished

417
00:17:29,015 --> 00:17:32,050
as the Permian forests
collapsed--fungi.

418
00:17:32,051 --> 00:17:35,020
A thin layer of extremely
abundant fungal remains

419
00:17:35,021 --> 00:17:37,489
is widespread
in geological formations

420
00:17:37,490 --> 00:17:39,591
that date
to the mass extinction.

421
00:17:39,592 --> 00:17:41,493
They're evidence
of a fungal spike

422
00:17:41,494 --> 00:17:44,196
across Pangea
as decomposers exploded

423
00:17:44,197 --> 00:17:47,332
to feast on the abundance
of dead vegetation.

424
00:17:47,333 --> 00:17:49,802
This fungal spike was
relatively short-lived,

425
00:17:49,803 --> 00:17:51,937
just a few thousand years
or so judging

426
00:17:51,938 --> 00:17:54,039
by the thickness of the layer
in the fossil record.

427
00:17:54,040 --> 00:17:55,741
But the weird thing--
and this is something

428
00:17:55,742 --> 00:17:57,910
that I think
it took me a while

429
00:17:57,911 --> 00:17:59,812
to understand--
what we're starting

430
00:17:59,813 --> 00:18:02,548
to see is that after
a while there's no food left

431
00:18:02,549 --> 00:18:05,184
for the decomposers
to decompose.

432
00:18:05,185 --> 00:18:07,786
Most of the time
during an extinction event,

433
00:18:07,787 --> 00:18:09,688
it's what suddenly disappears

434
00:18:09,689 --> 00:18:11,957
from the fossil record
that's most telling,

435
00:18:11,958 --> 00:18:13,859
but for the forests
of the Permian,

436
00:18:13,860 --> 00:18:16,528
it's what suddenly shows up
in the fossil record

437
00:18:16,529 --> 00:18:19,665
that actually tells the story
of their dramatic decline--

438
00:18:19,666 --> 00:18:22,468
spikes of charcoal,
mutated pollen,

439
00:18:22,469 --> 00:18:25,037
and global fungal blooms.

440
00:18:30,577 --> 00:18:32,110
The collapse
of the forests

441
00:18:32,111 --> 00:18:34,713
and increasing heat, drought,
and aridity pulled

442
00:18:34,714 --> 00:18:36,515
the ecological rug out
from under the feet

443
00:18:36,516 --> 00:18:37,983
of the Late Permian animal life.

444
00:18:37,984 --> 00:18:39,685
The effects
of the Permo-Triassic

445
00:18:39,686 --> 00:18:41,920
mass extinction,
or the Great Dying,

446
00:18:41,921 --> 00:18:43,989
on land were
really profound.

447
00:18:43,990 --> 00:18:46,959
So as a starting point,
you can say about 70%

448
00:18:46,960 --> 00:18:48,994
of terrestrial
vertebrate species

449
00:18:48,995 --> 00:18:50,963
that we know of
at the time went extinct.

450
00:18:50,964 --> 00:18:53,232
So a very large
die-off of animals.

451
00:18:53,233 --> 00:18:55,133
As we've seen
in earlier episodes,

452
00:18:55,134 --> 00:18:57,870
the Permian saw many land
animal lineages rise

453
00:18:57,871 --> 00:18:59,838
from humble beginnings
to some of the largest

454
00:18:59,839 --> 00:19:01,373
and most specialized animals

455
00:19:01,374 --> 00:19:03,408
that the terrestrial world
had ever seen,

456
00:19:03,409 --> 00:19:06,078
but when disaster struck,
these hard-won traits

457
00:19:06,079 --> 00:19:08,180
were actually a liability.

458
00:19:08,181 --> 00:19:10,849
Smaller and more generalist
species tend to do better

459
00:19:10,850 --> 00:19:12,618
than bigger
and more specialized ones

460
00:19:12,619 --> 00:19:13,986
in chaotic times.

461
00:19:13,987 --> 00:19:15,587
If you are
dependent

462
00:19:15,588 --> 00:19:17,456
on a specific
prey species

463
00:19:17,457 --> 00:19:20,392
or plant and that
goes extinct,

464
00:19:20,393 --> 00:19:21,727
you're in trouble.

465
00:19:21,728 --> 00:19:23,128
Populations
of big herbivores

466
00:19:23,129 --> 00:19:25,030
from both the reptile
and synapsid side

467
00:19:25,031 --> 00:19:27,766
of the family tree collapsed
alongside their habitats

468
00:19:27,767 --> 00:19:29,701
as the vegetation they
relied on withered,

469
00:19:29,702 --> 00:19:31,436
burned, and rotted away.

470
00:19:31,437 --> 00:19:34,139
Take the lumbering armored
pareiasaurs, for example.

471
00:19:34,140 --> 00:19:36,141
They were a group
of herbivorous reptiles

472
00:19:36,142 --> 00:19:38,043
that had been abundant
in the Late Permian,

473
00:19:38,044 --> 00:19:40,012
finding enormous success
munching their way

474
00:19:40,013 --> 00:19:41,980
through the plant life
of Pangea.

475
00:19:41,981 --> 00:19:43,482
There's research
that colleagues

476
00:19:43,483 --> 00:19:45,117
and I have done
actually modeling

477
00:19:45,118 --> 00:19:47,152
how disturbances
to food chains

478
00:19:47,153 --> 00:19:49,087
can cause extinction,
essentially

479
00:19:49,088 --> 00:19:50,756
that cascading process,

480
00:19:50,757 --> 00:19:52,791
and one of the things
that we found is

481
00:19:52,792 --> 00:19:54,760
really the most
effective way
to kill off

482
00:19:54,761 --> 00:19:56,728
a really big swath
of the community

483
00:19:56,729 --> 00:19:58,463
is to remove
the plants.

484
00:19:58,464 --> 00:19:59,765
start removing
the plants,

485
00:19:59,766 --> 00:20:01,199
and everything else
unravels.

486
00:20:01,200 --> 00:20:03,135
On our proto-mammal side
of the family tree,

487
00:20:03,136 --> 00:20:04,970
the picture was pretty similar--

488
00:20:04,971 --> 00:20:07,639
bigger and more specialized
species died out en masse,

489
00:20:07,640 --> 00:20:09,641
suddenly wiping out
many lineages

490
00:20:09,642 --> 00:20:11,209
that had been at the top
of their game

491
00:20:11,210 --> 00:20:13,245
like the dicynodonts,
for example.

492
00:20:13,246 --> 00:20:14,913
Kenneth Angielczyk:
Dicynodonts in general are

493
00:20:14,914 --> 00:20:16,315
a very diverse group,
particularly

494
00:20:16,316 --> 00:20:18,050
in the Permian period
of Earth history.

495
00:20:18,051 --> 00:20:21,186
{\an8}So there is about
150 dicynodont species

496
00:20:21,187 --> 00:20:23,021
{\an8}that have been named
over the years,

497
00:20:23,022 --> 00:20:25,924
{\an8}and they come in a really wide
range of shapes and sizes.

498
00:20:25,925 --> 00:20:27,492
So the smallest
dicynodonts are things

499
00:20:27,493 --> 00:20:28,894
like this little guy.

500
00:20:28,895 --> 00:20:30,329
This is a little skull
of an animal

501
00:20:30,330 --> 00:20:31,797
called Emydorhinus.

502
00:20:31,798 --> 00:20:33,298
It would be a roughly
guinea pig-sized animal.

503
00:20:33,299 --> 00:20:34,633
Wow.

504
00:20:34,634 --> 00:20:36,168
And the very biggest
dicynodonts

505
00:20:36,169 --> 00:20:37,603
get up to the size
of a large rhino

506
00:20:37,604 --> 00:20:39,104
or a small elephant.

507
00:20:39,105 --> 00:20:40,973
But dicynodonts were
almost entirely erased

508
00:20:40,974 --> 00:20:42,941
as the vegetation
they relied on disappeared,

509
00:20:42,942 --> 00:20:45,077
Only basically
4 lineages

510
00:20:45,078 --> 00:20:47,245
or kind of family groups
of dicynodonts

511
00:20:47,246 --> 00:20:48,513
actually survive.

512
00:20:48,514 --> 00:20:50,182
And while some
of these strange cousins

513
00:20:50,183 --> 00:20:51,883
of ours survived
for the remainder

514
00:20:51,884 --> 00:20:53,852
of the Triassic Period
before eventually dying out too,

515
00:20:53,853 --> 00:20:55,821
they'd never recapture
the level of diversity

516
00:20:55,822 --> 00:20:57,856
that they'd had in the Permian.

517
00:20:57,857 --> 00:20:59,891
Large carnivorous
therapsids were also hit hard

518
00:20:59,892 --> 00:21:01,226
during the Great Dying,

519
00:21:01,227 --> 00:21:03,161
like the saber-toothed
gorgonopsians,

520
00:21:03,162 --> 00:21:05,397
who had been at the top
of the Late Permian food chain.

521
00:21:05,398 --> 00:21:08,000
Apex predators
occupy in a way

522
00:21:08,001 --> 00:21:11,136
a very precarious position
in their communities.

523
00:21:11,137 --> 00:21:13,872
Because of the way
energy transfer scales,

524
00:21:13,873 --> 00:21:16,141
as you move up
the food chain,

525
00:21:16,142 --> 00:21:19,211
you need a very large
base of primary producers

526
00:21:19,212 --> 00:21:21,380
like plants and
smaller food sources

527
00:21:21,381 --> 00:21:24,016
to sort of supply
smaller animals

528
00:21:24,017 --> 00:21:26,818
to support a small
number of apex predators,

529
00:21:26,819 --> 00:21:29,688
and when things
start going bad,

530
00:21:29,689 --> 00:21:31,390
all of that makes
you vulnerable.

531
00:21:31,391 --> 00:21:33,425
The complex,
multidimensional ecosystems

532
00:21:33,426 --> 00:21:35,293
that had painstakingly evolved
over the course

533
00:21:35,294 --> 00:21:37,763
of the Permian came
crashing down,

534
00:21:37,764 --> 00:21:39,297
and it would take
millions of years

535
00:21:39,298 --> 00:21:43,035
for the biodiversity
of planet Earth to recover.

536
00:21:43,036 --> 00:21:45,937
The tree of life had
been brutally pruned.

537
00:21:45,938 --> 00:21:50,208
In total, over 80%
of species were now extinct,

538
00:21:50,209 --> 00:21:54,112
and whole ancient branches
were gone forever.

539
00:21:54,113 --> 00:21:56,882
Life was down but not fully out

540
00:21:56,883 --> 00:21:59,284
because from
the desperate survivors

541
00:21:59,285 --> 00:22:01,586
of the Great Dying
would emerge some

542
00:22:01,587 --> 00:22:07,392
of the most successful
animal dynasties of all time.

543
00:22:07,393 --> 00:22:10,295
The dinosaurs would soon
take the ecological spotlight

544
00:22:10,296 --> 00:22:12,297
in the new Mesozoic Era
that had begun,

545
00:22:12,298 --> 00:22:14,766
and eventually,
the mammals would follow.

546
00:22:14,767 --> 00:22:16,468
See, also among
the survivors was

547
00:22:16,469 --> 00:22:19,171
an obscure group
of small generalist therapsids

548
00:22:19,172 --> 00:22:20,806
that reached up
to around the size

549
00:22:20,807 --> 00:22:23,175
of a large meerkat
called cynodonts.

550
00:22:23,176 --> 00:22:25,110
They were
a group that wasn't

551
00:22:25,111 --> 00:22:28,780
terribly diverse
and relatively rare
in the Permian,

552
00:22:28,781 --> 00:22:30,816
but they really don't
show much drop-off

553
00:22:30,817 --> 00:22:32,184
in diversity as you
go through that

554
00:22:32,185 --> 00:22:33,785
extinction event.
Really?

555
00:22:33,786 --> 00:22:34,986
They just sort of
go through

556
00:22:34,987 --> 00:22:36,321
and do their thing,

557
00:22:36,322 --> 00:22:37,923
and when they get
to the Triassic

558
00:22:37,924 --> 00:22:39,191
and ecosystems are
sort of reorganizing,

559
00:22:39,192 --> 00:22:40,926
they really start
to diversify.

560
00:22:40,927 --> 00:22:42,327
Cynodonts
are the only group

561
00:22:42,328 --> 00:22:44,129
of Permian synapsids
that have survived

562
00:22:44,130 --> 00:22:45,931
until today in the form
of their direct descendants,

563
00:22:45,932 --> 00:22:47,966
us mammals,
and the question of why

564
00:22:47,967 --> 00:22:49,634
our cynodont ancestors
just happened to be

565
00:22:49,635 --> 00:22:51,870
among the small fraction
of life that survived

566
00:22:51,871 --> 00:22:54,072
is hard to know for sure.

567
00:22:54,073 --> 00:22:55,874
So they're relatively
advanced animals

568
00:22:55,875 --> 00:22:57,342
for their time.

569
00:22:57,343 --> 00:22:59,044
They have relatively
complicated teeth

570
00:22:59,045 --> 00:23:00,645
that allows them
to eat a variety

571
00:23:00,646 --> 00:23:01,980
of kinds of food.

572
00:23:01,981 --> 00:23:03,381
They have a little
bit larger brain,

573
00:23:03,382 --> 00:23:05,083
so probably a little
more adaptable

574
00:23:05,084 --> 00:23:07,018
and behaviorally
flexible.

575
00:23:07,019 --> 00:23:08,987
A lot of the early
cynodonts can construct

576
00:23:08,988 --> 00:23:12,190
burrows to live in
and potentially hibernate

577
00:23:12,191 --> 00:23:14,226
to get out
of bad conditions,

578
00:23:14,227 --> 00:23:16,495
so that kind of
generalist ecology

579
00:23:16,496 --> 00:23:18,196
is a good way
to survive extinctions.

580
00:23:18,197 --> 00:23:19,898
If you can be
sort of good

581
00:23:19,899 --> 00:23:22,134
at almost everything,
no matter what nature

582
00:23:22,135 --> 00:23:24,269
throws at you,
you're sort of
prepared for it.

583
00:23:24,270 --> 00:23:26,638
But perhaps dumb luck
and sheer chance

584
00:23:26,639 --> 00:23:28,173
played a role, too.

585
00:23:28,174 --> 00:23:30,242
While the worst
catastrophe of all time

586
00:23:30,243 --> 00:23:32,377
set the stage
for the rise of us mammals

587
00:23:32,378 --> 00:23:34,546
by taking out a lot
of the competition,

588
00:23:34,547 --> 00:23:36,848
it would be a mistake
to assume that things were

589
00:23:36,849 --> 00:23:39,317
just destined
to work out that way.

590
00:23:39,318 --> 00:23:41,520
Natural history is messy,

591
00:23:41,521 --> 00:23:43,655
full of unpredictable
situations,

592
00:23:43,656 --> 00:23:45,991
butterfly effects,
and changes of fortune

593
00:23:45,992 --> 00:23:48,026
that were far from inevitable

594
00:23:48,027 --> 00:23:50,262
and could have gone
down very differently,

595
00:23:50,263 --> 00:23:52,164
so if the events
of the End-Permian

596
00:23:52,165 --> 00:23:54,566
could be replayed,
who knows if the Great Dying

597
00:23:54,567 --> 00:23:57,235
might have been the end
of our story, too?

598
00:23:57,236 --> 00:23:58,770
I know you're
a scientist,

599
00:23:58,771 --> 00:24:00,372
but can I ask you to
speculate with me?

600
00:24:00,373 --> 00:24:02,407
I am dying to know
what would--

601
00:24:02,408 --> 00:24:04,242
maybe dying is
too strong a word.

602
00:24:04,243 --> 00:24:05,977
Those burrowing
generalists were

603
00:24:05,978 --> 00:24:07,712
our direct ancestors, right?

604
00:24:07,713 --> 00:24:10,215
What if things had gone
differently for them?

605
00:24:10,216 --> 00:24:12,784
How would the world be
a different place now?

606
00:24:12,785 --> 00:24:14,119
Would we be here?

607
00:24:14,120 --> 00:24:15,453
Well, the answer's easy.

608
00:24:15,454 --> 00:24:17,322
No. We would've not seen
the evolution

609
00:24:17,323 --> 00:24:20,625
of true mammals,
and we would not be here.

610
00:24:23,529 --> 00:24:25,597
Sometimes, we have
a tendency to separate

611
00:24:25,598 --> 00:24:27,332
ourselves from nature.

612
00:24:27,333 --> 00:24:29,467
We forget that we're
a part of Earth's history,

613
00:24:29,468 --> 00:24:31,336
that we are part
of geologic history,

614
00:24:31,337 --> 00:24:33,738
and even though
Salt Lake City is just

615
00:24:33,739 --> 00:24:36,908
a few minutes away,
so many people may not realize

616
00:24:36,909 --> 00:24:38,643
that when they run past here

617
00:24:38,644 --> 00:24:41,446
that they're running over
a marker of one

618
00:24:41,447 --> 00:24:44,149
of the worst events
in our history,

619
00:24:44,150 --> 00:24:46,618
and admittedly,
it is kind of

620
00:24:46,619 --> 00:24:48,587
unremarkable at first
When you walk past.

621
00:24:48,588 --> 00:24:51,189
It looks like every other
rock that you may

622
00:24:51,190 --> 00:24:53,892
walk by or cycle by,
but it reminds us

623
00:24:53,893 --> 00:24:57,095
that we could easily not be here

624
00:24:57,096 --> 00:24:59,164
and also just shows us
that, again,

625
00:24:59,165 --> 00:25:01,266
life is so resilient.

626
00:25:02,501 --> 00:25:05,203
More than anything, though,
this thin boundary

627
00:25:05,204 --> 00:25:07,372
is a reminder
that while biodiversity

628
00:25:07,373 --> 00:25:09,908
painstakingly develops
over vast stretches

629
00:25:09,909 --> 00:25:12,510
of geologic time,
extinction takes

630
00:25:12,511 --> 00:25:15,348
just a blink
of an evolutionary eye.