The oldest fossils of land plants are 420 million years old, but a recent study showed that pond scum first made landfall approximately 100 million years earlier.
Scientists have used plant genetic data at “molecular clocks” to estimate how long ago various species split based upon their differences in DNA—to figure out their evolutionary history. However, they were unable to identify the lowest, or earliest, branches of the plant family tree. Vascular plants such as trees, crops, and flowers have been known to come along sometime after liverworts, hornworts, and mosses. However, the order in which of these three appeared remained a history, making the molecular clock studies with missing puzzle pieces.
In the study conducted by Philip Donoghue from University of Bristol and other researchers, it was concluded that the exact configuration of the base of the plant family tree doesn’t matter to dating the first land plants. All the analyses indicate that land plants first appeared about 500 million years ago, during the Cambrian period, when the development of multicellular animal species took off. The study showed that the first land plants arose earlier than we thought, regardless of current uncertainties about which land plants evolved first. This finding has important global implications, because we know early plants cooled the climate and increased the oxygen level in the Earth’s atmosphere,” conditions that supported the expansion of terrestrial animal life, says Tim Lenton, an earth system scientist at the University of Exeter in the United Kingdom who was not involved with the work.