A new study published in the journal ‘Proceedings of the National Academy of Sciences’ has suggested plants greened the earth more than 100 millions years earlier than currently thought.
Previous studies have used ancient plant fossils, the oldest which have been dated to c. 420 millions years ago. The new study uses ‘molecular clock’ analysis which is deemed more accurate and suggests plants were on earth c. 500 million years ago. This would also affect the potential history of animals given that the plants provided the means for the first animals to crawl out of the sea and survive. The presence of greenery on earth would also have affected the climate and the chemical weathering of continental rocks over millions of years.
Prior to plants, scientists believe that the earth was sparse for c. 4 billion years and inhabited only by microbes.
“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.” said Mark Puttick, from the University of Bristol. “These relative genetic differences were then converted into ages by using the fossil ages as a loose framework.”
“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.”
The “molecular clock” method is based on the premise that certain genetic mutations accumulate at a predictable rate over time. By extrapolating back, they can be used to work out when life-forms diverged into different species.