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Six Degrees Separate Our World from the Cataclysmic End of an Ancient Era
by
George Monbiot
July
15, 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, paleontologists 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 paleontology 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 is Honorary Professor at
the Department of Politics in Keele and Visiting Professor at the Department of
Environmental Science at the University of East London. He writes a weekly
column for the Guardian newspaper of London. His recently released book, The
Age of Consent (Flamingo Press), puts forth proposals for global democratic governance. His articles and
contact info can be found at his website: 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