First Plants Colonized Earth 100 Million Years Earlier Than Previously Thought

The first plants to colonize the Earth originated around 500 million years ago – 100 million years earlier than previously thought, according to a new study from the University of Bristol.

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 and the timing of this episode has previously relied on the oldest fossil plants which are about 420 million years old.

These events actually occurred a hundred million years earlier, changing perceptions of the evolution of the Earth’s biosphere.

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.

“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.” said Mark Puttick, co- author who described the team’s approach to produce the timescale.

“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.”

Researchers say that ‘molecular clock’ methodology, combines evidence on the genetic differences between living species and fossil constraints on the age of their shared ancestors, to establish an evolutionary timescale that sees through the gaps in the fossil record.

“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 Dr 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.”

Research is published in the journal Proceedings of the National Academy of Sciences USA.

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