MCP wrote:

> http://observer.guardian.co.uk/uk_news/story/0,6903,1436408,00.html
>
> Robin McKie, science editor
> Sunday March 13, 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.'

I thought we knew what the cause was.

D.

> 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.'
>
>
>


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