<Plants Arrived Early

Earth story: Plants arrived early

Plants colonised land hundreds of millions of years earlier than the fossil record suggests, according to scientists in North America.

Genetic evidence gleaned from living species puts the date when land plants first evolved at about 700 million years ago.

This coincides with the time when the planet was thought to be entombed in ice, the so-called Snowball Earth, a dramatic climate reversal that preceded animal life on land.

Researchers from Pennsylvania State University say the presence of plants may have altered the Earth's climate, triggered the big freeze, and paved the way for the evolution of land animals....

[implications for the Cambrian 'explosion']

"Both the lowering of the Earth's surface temperature and the evolution of many new types of animals could result from a decrease in atmospheric carbon dioxide and a rise in oxygen caused by the presence on land of lichen fungi and plants at this time, which our research suggests.

"An increase in land plant abundance may have occurred at the time just before the period known as the Cambrian Explosion, when the next Snowball Earth period failed to occur because temperatures did not get cold enough," he added.

"The plants conceivably boosted oxygen levels in the atmosphere high enough for animals to develop skeletons, grow larger and diversify."

[extraterrestrial life implications?]

The work, published in the journal Science, could even help in the search for extraterrestrial life.

"Possibly, the early history of life on Earth can give us clues for predicting the kinds of lifeforms that are likely to exist on planets in other solar systems from the chemical content of their atmospheres," said Dr Hedges.

Linda Graham, an evolutionary biologist at the University of Wisconsin, said the findings were "surprising and very exciting"....