Insect deaths add to extinction fears
British survey hints that species are crashing worldwide.
19 March 2004
MICHAEL HOPKIN

Ecologists have unveiled strong evidence that huge numbers of the world's
species are disappearing. A survey of British wildlife suggests that
insects - thought to be among the most resilient species - are suffering
similar extinction rates to larger, better-studied animals.

If the same is happening worldwide, we may be witnessing the largest die-off
since the mass extinction that killed the dinosaurs, says Jeremy Thomas of
the Centre for Ecology and Hydrology in Dorset, UK, who led the study in
this week's Science1.

Thomas's team analysed surveys of British birds, plants and butterflies
stretching back 40 years. The statistics, collected by 20,000 amateur
naturalists, form an unprecedented census of insects. "No dataset approaches
this detail and scale anywhere in the world," Thomas says.

The researchers divided Britain into 10-kilometre squares and counted the
number of squares occupied by each species. Of 58 butterfly species, 71%
have declined or disappeared over the past 20 years, alongside 54% of birds.
The past 40 years has seen declines in 28% of plants studied.

Experts had assumed that the sheer number of insects would safeguard them
against mass extinction. "The gloomy result is that this group has declined
massively," says Thomas. As insects comprise more than 50% of the planet's
species, a large die-off would be bad news for global diversity, he adds.

Read the rest at Nature
http://www.nature.com/nsu/040315/040315-11.html

Did cracking continent trigger a deep freeze?
The break-up of a supercontinent may have caused a 'Snowball Earth'.
18 March 2004
PHILIP BALL

The Earth might have been sent into an ice age by the break-up of a
supercontinent 750 million years ago, creating a global snowball.

The break-up probably caused an increase in rainfall and weathering of rock,
say climatologists. This would have sucked greenhouse gases out of the
atmosphere and caused a run-away cooling effect. The mechanism could explain
how the entire planet becomes encased in a mass of ice, as many researchers
think it has done in the past.

The theory that the Earth was once completely frozen emerged in the 1960s,
when scientists realised that global freezing could happen if the polar ice
sheets grew above a certain threshold size. Because bright ice reflects
sunlight and heat back into space, growing ice sheets cause further cooling.
This feedback loop could tip the climate system into a deep freeze.

The planet could eventually thaw as carbon dioxide from volcanoes poking
through the ice warm it.

In the late 1980s, Joe Kirschvink of the California Institute of Technology
nicknamed this state 'Snowball Earth'. Around the same time, geologists
began to uncover hints in the geological record that this freeze-thaw
process might have happened at least once in the distant past - at the end
of the Proterozoic eon, 600 to 800 million years ago.

But it was unclear what could have tipped the world into that state in the
first place. Now Yannick Donnadieu of the Laboratoire des Sciences du Climat
et de l'Environnement in Gif sur Yvette, France, and co-workers provide an
explanation in this week's Nature1.

http://www.nature.com/nsu/040315/040315-7.html

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