Shadow
Of Extinction
By
George Monbiot
Znet
22 July, 2003
It
is old news, I admit. Two hundred and fifty-one million years old, to
be precise. But the story of what happened then, which has now been
told for the first time, demands our urgent attention. Its implications
are more profound than anything taking place in Iraq, or Washington,
or even (and I am sorry to burst your bubble) Wimbledon. Unless we understand
what happened, and act upon that intelligence, pre-history may very
soon repeat itself, not as tragedy, but as catastrophe.
The events which
brought the Permian period (between 286 and 251 million years ago) to
an end could not be clearly determined until the mapping of the key
geological sequences had been completed. Until recently, palaeontologists
had assumed that the changes which took place then were gradual and
piecemeal. But three years ago a precise date for the end of the period
was established, which enabled geologists to draw direct comparisons
between the rocks laid down at that time in different parts of the world.
Having done so,
they made a shattering discovery. In China, South Africa, Australia,
Greenland, Russia and Spitsbergen, the rocks record an almost identical
sequence of events, taking place not gradually, but almost instantaneously.
They show that a cataclysm caused by natural processes almost brought
life on earth to an end. They also suggest that a set of human activities
which threatens to replicate those processes could exert the same effect,
within the lifetimes of some of those who are on earth today.
As the professor
of palaeontology Michael Benton records in his new book, When Life Nearly
Died, the marine sediments deposited at the end of the Permian period
record two sudden changes.1 The first is that the red or green or grey
rock laid down in the presence of oxygen is suddenly replaced by black
muds of the kind deposited when oxygen is absent. At the same time,
an instant shift in the ratio of the isotopes (alternative forms) of
carbon within the rocks suggests a spectacular change in the concentration
of atmospheric gases.
On land, another
dramatic transition has been dated to precisely the same time. In Russia
and South Africa, gently deposited mudstones and limestones suddenly
give way to massive dumps of pebbles and boulders. But the geological
changes are minor by comparison to what happened to the animals and
plants.
The Permian was
one of the most biologically diverse periods in the earth's history.
Herbivorous reptiles the size of rhinos were hunted through forests
of tree ferns and flowering trees by sabre-toothed predators. At sea,
massive coral reefs accumulated, among which lived great sharks, fish
of all kinds and hundreds of species of shelly creatures.
Then suddenly there
is almost nothing. The fossil record very nearly stops dead. The reefs
die instantly, and do not reappear on earth for ten million years. All
the large and medium-sized sharks disappear, most of the shelly species,
and even the great majority of the toughest and most numerous organisms
in the sea, the plankton. Among many classes of marine animals, the
only survivors were those adapted to the near-absence of oxygen.
On land, the shift
was even more severe. Plant life was almost eliminated from the earth's
surface. The four-footed animals, the category to which humans belong,
were nearly exterminated: so far only two fossil reptile species have
been found anywhere on earth which survived the end of the Permian.
The world's surface came to be dominated by just one of these, an animal
a bit like a pig. It became ubiquitous because nothing else was left
to compete with it or to prey upon it.
Altogether, Benton
shows, some 90% of the earth's species appear to have been wiped out:
this represents by the far the gravest of the mass extinctions. The
world's "productivity" (the total mass of biological matter)
collapsed.
Ecosystems recovered
very slowly. No coral reefs have been found anywhere on earth in the
rocks laid down over the following 10 million years. One hundred and
fifty million years elapsed before the world once again became as biodiverse
as it appears to have been in the Permian. So what happened?
Some scientists
have argued that the mass extinction was caused by a meteorite. But
the evidence they put forward has been undermined by further studies.
There is a more persuasive case for a different explanation. For many
years, geologists have been aware that at some point during or after
the Permian there was a series of gigantic volcanic eruptions in Siberia.
The lava was dated properly for the first time in the early 1990s. We
now know that the principal explosions took place 251 million years
ago, precisely at the point at which life was almost extinguished.
The volcanoes produced
two gases: sulphur dioxide and carbon dioxide. The sulphur and other
effusions caused acid rain, but would have bled from the atmosphere
quite quickly. The carbon dioxide, on the other hand, would have persisted.
By enhancing the greenhouse effect, it appears to have warmed the world
sufficiently to have destabilised the super concentrated frozen gas
called methane hydrate, locked in sediments around the polar seas. The
release of methane into the atmosphere explains the sudden shift in
carbon isotopes.
Methane is an even
more powerful greenhouse gas than carbon dioxide. The result of its
release was runaway global warming: a rise in temperature led to changes
which raised the temperature further, and so on. The warming appears,
alongside the acid rain, to have killed the plants. Starvation then
killed the animals.
Global warming also
seems to explain the geological changes. If the temperature of the surface
waters near the poles increases, the circulation of marine currents
slows down, which means that the ocean floor is deprived of oxygen.
As the plants on land died, their roots would cease to hold together
the soil and loose rock, with the result that erosion rates would have
greatly increased. So how much warming took place? A sharp change in
the ratio of the isotopes of oxygen permits us to reply with some precision:
six degrees centigrade. Benton does not make the obvious point, but
another author, the climate change specialist Mark Lynas, does.2 Six
degrees is the upper estimate produced by the UN's scientific body,
the Intergovernmental Panel on Climate Change, for global warming by
2100.3
A conference of
some of the world's leading atmospheric scientists in Berlin last month
concluded that the IPCC's model may have underestimated the problem:
the upper limit, they now suggest, should range between 7 and 10 degrees.4
Neither model takes into account the possibility of a partial melting
of the methane hydrate still present in vast quantities around the fringes
of the polar seas.
Suddenly, the events
of a quarter of a billion years ago begin to look very topical indeed.
One of the possible endings of the human story has already been told.
Our principal political effort must now be to ensure that it does not
become set in stone.
George Monbiot's
book The Age
of Consent: a Manifesto for a New World Order is published by Flamingo.
www.monbiot.com References:
1. Michael J. Benton,
2003. When Life Nearly Died: The Greatest Mass Extinction of All Time.
Thames and Hudson, London.
2. Press Release
issued by Mark Lynas, 17th June 2003. "New Evidence Warns of Global
Warming 'Catastrophe' this Century".
3. Eg Robert Watson,
chairman IPCC, 20th November 2000. Report to the Sixth Conference of
the Parties of the United Nations Framework Convention on Climate Change.
4. Fred Pearce, 4th June 2003. Global Warming's Sooty Smokescreen Revealed.
New Scientist. http://www.newscientist.com/news/news.jsp?id=ns99993798