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Last Updated: Monday, 13 October, 2003, 16:49 GMT 17:49 UK
Life's lucky 'kick start'
By Dr David Whitehouse
BBC News Online science editor

The Cambrian Explosion - when life suddenly and rapidly flourished some 550 million years ago - may have an explanation in the reaction of primitive life to some big event.

The Cambrian period followed global change
Something triggered the explosion of life
The explosion is one of the most significant yet least understood periods in the history of life on Earth.

New research suggests it may have occurred because of a complex interaction between components of the biosphere after they had been disturbed by, for example, the break-up of a super-continent or an asteroid impact.

Scientists say the life explosion might just have easily occurred two billion years earlier - or not at all.

Dramatic events

All modern forms of life have their origin in the sudden diversification of organisms that occurred at the end of the so-called Cryptozoic Eon.

Scientists have struggled to explain what might have happened in the previous few hundred million years to trigger such a burst of life.

BIOLOGY'S 'BIG BANG'
Trilobite, Manitoba Museum
Major animal groups, or phyla, trace lineage to Cambrian Period
Age of trilobites, sea-dwelling arthropods used to date rock layers
Medieval Latin name for Wales, where Cambrian rocks first described
Certainly, it was a period of history that witnessed the assembly and break-up of two super continents and at least two major glaciation events. Atmospheric oxygen levels were also on the rise.

But what actually caused the Cambrian Explosion is unknown.

Writing in the journal Geophysical Research Letters, Dr Werner von Bloh and colleagues, from the Potsdam Institute for Climate Impact Research, present a new analysis of happened.

They suggest that "feedback" in the biosphere caused it to jump from one stable state without complex life to one that allowed complicated life to proliferate.

"We believe that there was a change in the environment - a slow cooling of the system - that caused positive feedback that allowed the conditions for complex life," Dr von Bloh told BBC News Online.

Self regulation

Using a computer model of the ancient Earth, the researchers considered three components of the biosphere, the zone of life.

These were single-celled life with and without a nucleus, and multicellular life. Each of these three groups have different environmental tolerances outside which they cannot thrive.

Computer model, Dr von Bloh
Simulating the primitive Earth's biosphere
The computer model showed there were two zones of stability for the Earth - with or without higher lifeforms - and that 542 million years ago the planet flipped from one to the other.

What caused the flip is not clear. It might have been a continental break-up, or even an asteroid impact.

There is some indication that the Moon suffered a sudden increase in impacts about the same time as the Cambrian Explosion. If so, then the Earth would have been affected as well.

This latest analysis also provides some support for the Gaia hypothesis - the idea that the biosphere somehow acts as a self-sustaining and regulating whole that opposes any changes that would destroy life on Earth.

Intelligent beings

Dr von Blow says that after the Cambrian Explosion there has been a stabilisation of temperature up to the present, and that the biosphere is not playing a passive role.

He also adds that there is an intriguing implication from his research which suggests that had the conditions been only slightly different, the Cambrian Explosion could have occurred two billion years earlier.

An early explosion would have meant that by now the Earth could have developed far more advanced intelligent creatures than humans.

Alternatively it could still be inhabited by nothing more complex than bacteria.

Dr von Bloh says that it will be of great interest when we find other Earth-like worlds circling other stars to see if they have had their own Cambrian explosions yet.

The timing of such events has implications for the search for intelligent life in space, he says.




SEE ALSO:
The microbes that 'rule the world'
28 Sep 01  |  Science/Nature
Earth story: Plants arrived early
09 Aug 01  |  Science/Nature
Asteroid 'destroyed life 250m years ago'
23 Feb 01  |  Science/Nature
Lunar meteorites reveal life's troubles
30 Nov 00  |  Science/Nature
How life survived the big freeze
25 May 00  |  Science/Nature


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