Image copyright Paul Kenrick Image caption Early plants would have looked much like this lava field in Iceland

A seminal event in the Earth's history - when plants appeared on land - may have happened 100 million years earlier than previously thought.

Land plants evolved from "pond scum" about 500 million years ago, according to new research.

These early moss-like plants greened the continents, creating habitats for land animals.

The study, based on analysing the genes of living plants, overturns theories based purely on fossil plant evidence.

"Land plants emerged on land half a billion years ago, tens of millions of years older than the fossil record alone suggests," said study author, Dr Philip Donoghue of the department of Earth Sciences at the University of Bristol.

"This changes perception of the nature of early terrestrial environments, displacing pond scum in favour of a flora that would have tickled your toes - but not reached much higher. "

Image copyright Natural History Museum, London Image caption Fossil plant stem dating back 400 million years from Aberdeenshire, Scotland

Early plants would have provided a habitat for fully terrestrial animals, which emerged onto land at much the same time, he said.

This coincides with the time period when life became more diverse and abundant in the seas - an event known as the Cambrian explosion.

"Our results show the ancestor of land plants was alive in the middle Cambrian Period, which was similar to the age for the first known terrestrial animals," said co-researcher Dr Mark Puttick, from the Natural History Museum, London.

Molecular clock

For the first four billion years of Earth's history, the continents would have been devoid of all life save microbes.

When land plants arose, they greened the continents and created habitats for animals.

The spread of plants around the world and their adaptations to life on land influenced levels of carbon dioxide in the atmosphere and global temperatures, sustaining all life on Earth.

The study, published in the journal, Proceedings of the National Academy of Sciences, calls into question existing theories on the evolution of land plants.

The researchers say the fossil ages underestimate the origins of land plants, and so these models need to be revised.

The new study is based on the so-called molecular clock method - analysing the genes of living organisms combined with knowledge from fossils about shared ancestors.

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