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70 April 2023 April 2023 71
B
udleigh Salterton, on the south coast of
Devon, sits above the most frightening
clis on Earth. They are not particularly
high. Though you don’t want to stand
beneath them, they are not especially
prone to collapse. The horror takes another form. It is
contained in the story they tell. For they capture the
moment at which life on Earth almost came to an end.
The sediments preserved in these clis were laid
down in the early Triassic period, just after the greatest
mass extinction in the history of multicellular life, that
brought the Permian period to an end 252m years ago.
Around 90% of species died, and fish and four-footed
animals were more or less exterminated between 30
degrees north of the equator and 40 degrees south.
Most remarkably, while biological abundance (if not
diversity) tends to recover from mass extinctions
CLIFF EDGE
By George Monbiot
Fossil-fuel burning precipitated mass
extinction in the Permian period and
will do so again unless we step back
from the precipice
Frightening Budleigh Sleron
within a few hundred thousand years, our planet
remained in this near-lifeless state for the following 5m
years. In studying these clis, you see the precipice on
which we teeter.
The lowest stratum at the western end of the beach
is a bed of rounded pebbles. These are the stones
washed o Triassic mountains by flash floods and
deposited in great dumps by temporary rivers. Because
the forests and savannahs that might have covered the
mountains had died, there was nothing to hold the soil
and subsoil together, so erosion is likely to have
accelerated greatly.
At the top of the pebble bed is a stony desert
surface. The pebbles here have been sculpted by the
wind into sha rp angles and varnished with shiny
oxides, suggesting the surface was unchanged for a
long time. Above it are towering red Triassic sand
dunes. Through a quirk of erosion, these soft deposits
have been sculpted into hollows that look uncannily
like fanged and screaming skulls.
We now know that there were two main pulses of
extinction. The first, which began 252.1m years ago,
mostly aected life on land. It coincided with a series
of massive volcanic eruptions in the region now known
as the Siberian Traps. The second, more devastating
phase, started about 200,000 years later. It almost
completed the extinction of terrestrial life, as well as
wiping out the great majority of species in the sea.
ENVIRONMENT
70 April 2023 April 2023 71
ancient sand dunes.
The story the clis tell is of planetary tipping points:
Earth systems pushed past their critical thresholds,
beyond which they collapsed into a new equilibrium
state, that could not be readily reversed. It was a world
hostile to almost all large life forms: the monsters of
the Permian were replaced nearly everywhere by dwarf
fauna.
Could it happen again? Two parallel and contradictory
processes are in play. At climate summits, governments
produce feeble voluntary commitments to limit the
production of greenhouse gases. At the same time,
almost every state with significant fossil reserves –
including the UK – intends to extract as much as they
can. A report by Carbon Tracker shows that if all the
world’s reserves of fossil fields were extracted, their
combustion would exceed the carbon budget
governments have agreed sevenfold. While less
carbon is contained in these reserves than the amount
produced during the Permian-Triassic extinction, the
compressed timescale could render this release just
as deadly to life on Earth. The increase in atmospheric
CO2 at the end of the Permian took about 75,000 years,
but many of our fossil fuel reserves could be consumed
in decades. Already, we seem to be approaching a
series of possible tipping points, some of which could
trigger cascading collapse.
Everything now hangs on which process prevails:
the sometimes well-meaning, but always feeble,
attempts to limit the burning of fossil carbon, or the
ruthless determination – often on the part of the same
governments – to extract (and therefore burn) as much
of it as possible, granting the profits of legacy
industries precedence over life on Earth. At the climate
summit in November in Egypt, which failed even to
agree to phase down oil and gas, we saw how close to
the cli edge the world’s governments are willing to
take us.
This article first appeared in the Guardian;
www.monbiot.com
Around 90% of species died in
the greatest mass extinction in
the history of multicellular life,
that brought the Permian period
to an end 252m years ago
The second phase
of the extinction
appears to have
been driven by
global heating
Though we cannot yet be sure, the first phase might
have been triggered by acid rain, ozone depletion and
metal pollution caused by volcanic chemicals. As
rainforests and other ecosystems were wiped out,
more toxic compounds were released from exposed
soils and rocks, creating an escalating cycle of
collapse.
The second phase appears to have been driven by
global heating. By 251.9m years ago, so much
solidified rock had accumulated on the surface of the
Siberian Traps that the lava could no longer escape.
Instead, it was forced to spread underground, along
horizontal fissures, into rocks that were rich in coal and
other hydrocarbons. The heat from the magma
(underground lava) cooked the hydrocarbons,
releasing vast amounts of carbon dioxide and
methane. In other words, though there were no humans
on the planet, this disaster seems to have been caused
by fossil fuel burning.
Temperatures are believed to have climbed by
between 8C and 10C, though much of the second
phase of extinction might have been caused by an
initial rise of between 3C and 5C. The extra carbon
dioxide also dissolved into the oceans, raising their
acidity to the point at which many species could no
longer survive. The temperature rise appears to have
brought ocean currents to a halt, through the same
mechanism that now threatens the Atlantic meridional
overturning circulation, which drives the Gulf Stream.
As wildfires ragedacross the planet, incinerating the
vegetation protecting its surface, ash and soil would
have poured into the sea, triggering eutrophication (an
excess of nutrients). In combination with the high
temperatures and stalled circulation, this starved the
remaining life forms of oxygen.
A paper released as a pre-print in September might
explain why recovery took so long. Because so many
of the world’s rich ecosystems had been replaced by
desert, plants struggled to re-establish themselves.
Their total weight on Earth fell by about two thirds.
Throughout these 5m years, no coal deposits formed,
as there wasn’t sucient plant production to make
peat bogs. In other words, the natural processes that
remove CO2 from the atmosphere and turn it into wood
and soil or bury it as fossil carbon stalled. For 5m years,
the world was trapped in this hothouse state. In the
clis at the eastern end of the bay, you can see when
conditions began, at last, to change, as the fossilised
roots of semi-desert plants twist down through the
Permin extinction: the pst nd mybe big prt of the future
