Fossils: The earliest green algae discovered

Millimetre-sized, multicellular green algal fossils from rocks dated to around 1,000 million years ago are described in a paper published in Nature Ecology & Evolution.

Green, photosynthesizing plants (Viridiplantae) are estimated (using molecular clocks and biomarker analyses) to have arisen sometime between the Palaeoproterozoic era (2,500 - 1,600 million years ago) and the Cryogenian period (720 - 635 million years ago). However, this date has been difficult to pinpoint owing to a lack of fossil evidence. Moreover, it is unknown when green plants developed multicellularity.

Qing Tang and colleagues report a new fossil species of green algae from the 1,000 million-year-old Nanfen Formation in Liaoning, China. Despite its ancient age, this species - named Proterocladus antiquus - shows a range of features consistent with present-day green algae, including multicellularity; differentiated, branched cells; and root-like structures.

The authors conclude that the discovery of P. antiquus helps to validate molecular clock estimates for earlier divergences in the plant kingdom. It could also help answer questions about energy capture in ancient oceans.