Scientists have found fossils of 1.6 billion-year-old probable red algae, which may be the oldest plant-like life discovered on Earth. Until now, the oldest known red algae was 1.2 billion years old from the Canadian Arctic.
The findings in Chitrakoot, Madhya Pradesh by researchers from the Swedish Museum of Natural History, published on 14 March in the open access journal PLOS Biology, indicate that advanced multicellular life evolved much earlier than previously thought.
Researchers described the tiny, multicellular fossils as two types of red algae, one thread-like and the other bulbous, that lived in a shallow marine environment alongside mats of bacteria. 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.
“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,” says Stefan Bengtson, Professor emeritus of palaeozoology at the Swedish Museum of Natural History.
No DNA remains in the fossils to be analysed. But the material structurally resembles red algae, embedded in fossil mats of cyanobacteria, called stromatolites, inside a 1.6 billion-year-old Indian phosphorite.
“You cannot be a hundred percent 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,” said Bengtson.
The researchers said cellular structures preserved in the fossils and their overall shape match red algae, a primitive kind of plant that today thrives in marine settings such as coral reefs but also can be found in freshwater environment. A type of rose algae known as nori is a common sushi ingredient.
“We almost could have had sushi 1.6 billion years ago,” joked Swedish Museum of Natural History geobiologist Therese Sallstedt, who helped lead the study.
The earliest traces of life on Earth are at least 3.5 billion years old. These single celled organisms, unlike eukaryotes, lack nuclei and other organelles. Large multicellular eukaryotic organisms became common much later, about 600 million years ago, near the transition to the Phanerozoic Era, the “time of visible life.”
This discovery could lead experts to rewrite the tree of life, said Bengston. “The ‘time of visible life’ seems to have begun much earlier than we thought,” he said.
Discoveries of early multicellular eukaryotes have been sporadic and difficult to interpret, challenging scientists trying to reconstruct and date the tree of life. The oldest known red algae before the present discovery are 1.2 billion years old. The Indian fossils, 400 million years older and by far the oldest plant-like fossils ever found, suggest that the early branches of the tree of life need to be recalibrated.
Sallstedt said, “Plants have a key role for life on Earth, and we show here that they were considerably older than what we knew, which has a ripple effect on our appreciation of when advanced life forms appeared on the evolutionary scene.”
The research group was able to look inside the algae with the help of synchrotron-based X-ray tomographic microscopy. Among other things, they have seen regularly recurring platelets in each cell, which they believe are parts of chloroplasts, the organelles within plant cells where photosynthesis takes place. They have also seen distinct and regular structures at the centre of each cell wall, typical of red algae.