London, Feb 20 (IANS): The first plants to colonise the Earth originated around 500 million years ago -- 100 million years earlier than previously thought, says a new study.
For the first four billion years of Earth's history, our planet's continents would have been devoid of all life except microbes.
All of this changed with the origin of land plants from their pond scum relatives, greening the continents and creating habitats that animals would later invade.
The timing of this episode has previously relied on the oldest fossil plants which are about 420 million years old.
The new study, published in the journal Proceedings of the National Academy of Sciences, indicates that these events actually occurred a hundred million years earlier, changing perceptions of the evolution of the Earth's biosphere.
"The fossil record is too sparse and incomplete to be a reliable guide to date the origin of land plants," said co-lead author Mark Puttick from University of Bristol in Britain.
"Instead of relying on the fossil record alone, we used a 'molecular clock' approach to compare differences in the make-up of genes of living species -- these relative genetic differences were then converted into ages by using the fossil ages as a loose framework," Puttick said.
The research pointed out that plants are major contributors to the chemical weathering of continental rocks, a key process in the carbon cycle that regulates Earth's atmosphere and climate over millions of years.
"The global spread of plants and their adaptations to life on land, led to an increase in continental weathering rates that ultimately resulted in a dramatic decrease the levels of the 'greenhouse gas' carbon dioxide in the atmosphere and global cooling," said Jennifer Morris, from the University of Bristol.
"Previous attempts to model these changes in the atmosphere have accepted the plant fossil record at face value - our research shows that these fossil ages underestimate the origins of land plants, and so these models need to be revised," Morris added.