Are We Past
Our 'Extinct By' Date?
By Robin McKie
13 March, 2005
The
Observer
Some
say the world will end in fire, some say in ice, wrote Robert Frost.
But whatever is to be our fate, it is now overdue.
After analysing
the eradication of millions of ancient species, scientists have found
that a mass extinction is due any moment now.
Their research has
shown that every 62 million years - plus or minus 3m years - creatures
are wiped from the planet's surface in massive numbers.
And given that the
last great extinction occurred 65m years ago, when dinosaurs and thousands
of other creatures abruptly disappeared, the study suggests humanity
faces a fairly pressing danger. Even worse, scientists have no idea
about its source.
'There is no doubting
the existence of this cycle of mass extinctions every 62m years. It
is very, very clear from analysis of fossil records,' said Professor
James Kirchner, of the University of California, Berkeley. 'Unfortunately,
we are all completely baffled about the cause.'
The report, published
in the current issue of Nature, was carried out by Professor Richard
Muller and Robert Rohde also from the Berkeley campus. They studied
the disappearances of thousands of different marine species (whose fossils
are better preserved than terrestrial species) over the past 500m years.
Their results were
completely unexpected. It was known that mass extinctions have occurred
in the past. During the Permian extinction, 250m years ago, more than
70 per cent of all species were wiped out, for example. But most research
suggested that these were linked to asteroid collisions and other random
events.
But Muller and Rohde
found that, far from being unpredictable, mass extinctions occur every
62m years, a pattern that is 'striking and compelling', according to
Kirchner.
But what is responsible?
Here, researchers ran into problems. They considered the passage of
the solar system through gas clouds that permeate the galaxy. These
clouds could trigger climatic mayhem. However, there is no known mechanism
to explain why the passage might occur only every 62m years.
Alternatively, the
Sun may possess an undiscovered companion star. It could approach the
Sun every 62m years, dislodging comets from the outer solar system and
propelling them towards Earth. Such a companion star has never been
observed, however, and in any case such a lengthy orbit would be unstable,
Muller says.
Or perhaps some
internal geophysical cycle triggers massive volcanic activity every
62m years, Muller and Rohde wondered. Plumes from these would surround
the planet and lead to a devastating drop in temperature that would
freeze most creatures to death.
Unfortunately, scientists
know of no such geological cycle.
'We have tried everything
we can think of to find an explanation for these weird cycles of biodiversity
and extinction,' Muller said. 'So far we have failed. And, yes, we are
due one soon, but I would not panic yet.'