An article published in the journal “Proceedings of the National Academy of Sciences” describes a research on the timeline of the mainland colonization by plants. A team of researchers led by the British University of Bristol used the molecular clock methodology to compare genetic differences among the various species even in the absence of complete fossils. The conclusion is that plants started colonizing the mainland about 100 million years earlier than previously thought based on the oldest fossils, which date back to about 420 million years ago.

The relationship among early plants are uncertain, so much that there are seven different hypotheses regarding the possible genealogy with different relationships among various groups. The members of the team from the University of Bristol were also part of another team that tried to reconstruct the most likely genealogy publishing the results in another article that appeared in the journal “Current Biology”.

The problem in this type of task is due to the scarcity of fossils, very common in the field of paleontology, especially when the research concerns organisms that lived in the Cambrian and in the Ordovician periods. In the case of plant colonization of the mainland, the oldest fossils date back to about 420 million years ago, but according to the Bristol-led researchers they’re not a reliable guide for the reconstruction of that event.

Mark Puttick, one of the authors of the research, explained that his team used a molecular clock-based approach. The genetic differences in today’s plants were used to estimate the time elapsed from the separation between them and reconstruct the ages of their common ancestors using fossils as references.

The two research leaders Philip Donoghue and Harald Schneider explained that to assess the unknowns connected to the doubts about the relationship among the various groups of plants the researchers made different reconstructions based on the various hypotheses. The result is that there were no significant differences in the estimated timelines for the origin of plants on the mainland.

Dr Jennifer Morris, also among the authors of the research, explained the importance of the plants spreading on the mainland pointing out the changes they caused in the atmosphere as well as those on the land. Knowing when plants occupied the mainland means understanding much better the evolution of the Earth’s atmosphere.