posted 10-01-2003 08:59 PM                         

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Plants detonated Cambrian explosion
Global cooling may have allowed complex animals to flourish.
1 October 2003

JOHN WHITFIELD

Early lichen-like plants could have increased erosion.
© GettyImages

The first land plants might have triggered a rush of animal evolution. German researchers are proposing a controversial theory that the plants cooled Earth, making it conducive to complex life1.

The idea is a new twist on the Gaia hypothesis that living things influence the global environment. "During the evolution of the Earth there was a decrease in temperature, and higher life forms have lower temperature limits," says Werner von Bloh of the Potsdam Institute for Climate Impact Research.

Many researchers think that rising, not falling, temperatures lit the fuse for the Cambrian explosion, the biological Big Bang 540 million years ago when most modern animal groups appear in the fossil record.

There is genetic evidence that simple plants, such as algae and lichens, colonized the land 800 million years ago. But no plant fossils from this time have been found.

It's also unclear whether there was a slump in temperatures, and whether such a drop would have favoured complex life. Says palaeontologist Robert Riding of Cardiff University, UK: "Nobody knows what's right or wrong, but it sounds odd to me".

But the link between temperature and life deserves further investigation, argues geochemist David Schwartzman of Howard University in Washington DC. "The global emergence of certain types of organism could be tied to their optimum temperature," he says.

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