[meteorite-list] Life's Lucky 'Kick Start'

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:28:27 2004
Message-ID: <200310131632.JAA01534_at_zagami.jpl.nasa.gov>

http://news.bbc.co.uk/1/hi/sci/tech/3181546.stm

Life's lucky 'kick start'
By Dr David Whitehouse
BBC News
October 13, 2003

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 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.

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.

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.
Received on Mon 13 Oct 2003 12:32:05 PM PDT