As we keep discovering new species (which aren’t actually new) of animals and plants that lived in the past and the present, we keep revising the tree of life to better understand how life originated on Earth and how it spread to the multitudes of life-forms that now inhabit the planet. In a significant finding in the field, the oldest plant-like fossils, from 1.6 billion years ago, were discovered in India.

Described in an open-access paper titled— “Three-dimensional preservation of cellular and subcellular structures suggests 1.6 billion-year-old crown-group red algae” — in the journal PLOS Biology, the fossils are “probable crown-group rhodophytes (red algae).” One of the two different kinds of algae is thread-like while the other has fleshy colonies. They were found in well-preserved sedimentary rocks in central India, in Chitrakoot, Uttar Pradesh.

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“You cannot be a hundred per cent sure about material this ancient, as there is no DNA remaining, but the characters agree quite well with the morphology and structure of red algae,” Stefan Bengtson from the Swedish Museum of Natural History, whose scientists made the findings, said in a statement. Bengtson was also lead author of the study.

X-ray tomographic picture (false colors) of fossil thread-like red algae. Stefan Bengtson

The oldest-known red algae fossil till now was dated to about 1.2 billion years ago, making the Indian specimens 400 million years older. Using a method called synchrotron-based X-ray tomographic microscopy, “the scientists were able to see distinct inner cell structures and so-called cell fountains, the bundles of packed and splaying filaments that form the body of the fleshy forms and are characteristic of red algae,” according to the statement. They also saw what they believe are parts of chloroplast, the organelle used for photosynthesis by plants.

The thread-like form of the presumed red algae was discovered first, and the fleshy colony variant was discovered later by Therese Sallstedt, a doctoral student and co-author of the study, who was investigating the fossil mats of cyanobacteria the algae were embedded in.

While life on Earth can be traced back to over 3.5 billion years ago (the planet itself is about 4.5 billion years old), it existed only in unicellular forms, called prokaryotes (bacteria and archaea), for between roughly 1.5 billion and two billion years. Multi-cellular life evolved about 2.1-1.6 billion years ago, but records of it from that long ago are rare and difficult to interpret. Large animals and plants came around only about 600 million years ago.

“The ‘time of visible life’ seems to have begun much earlier than we thought,” Bengtson said.