History

Ancient Plant-like Fossils Prove Multicellular Life Appeared Earlier Than Believed

multicelluar life

Fossils of 1.6 billion-year-old probable red algae have been found by researchers from the Swedish Museum of Natural History. This indicates that advanced multicellular life evolved earlier than previously believed.

Two kinds of fossils resembling red algae were found at Chitrakoot in central India. The fossils were both in exceptionally well-preserved sedimentary rocks. One type consists of fleshy colonies, while the other one is thread like. The scientists were able to see distinct so-called cell fountains and inner cell structures. Cell fountains are characteristic of red algae and consist of the bundles of splaying and packed filaments that form the body of the fleshy forms.

Stefan Bengtson, Professor emeritus of palaeozoology at the Swedish Museum of Natural History explained that with material this ancient, one could never be a hundred percent sure, as there is no remaining DNA. The characteristics do however compare well with the structure and morphology of red algae.

Tomographic X-ray picture (false colors) of fossil thread-like red algae. (Image Credit: Stefan Bengtson, CCAL)
Tomographic X-ray picture (false colors) of fossil thread-like red algae. (Image Credit: Stefan Bengtson, CCAL)

The oldest traces of life that has been found on Earth are at least 3.5 billion years old. These single celled organisms lack nuclei and other organelles, unlike eukaryotes. Large multicellular eukaryotic organisms only appeared much later, near the transition to the Phanerozoic Era about 600 million years ago. This time is known as the “time of visible life.”

Earlier discoveries of multicellular eukaryotes have been infrequent and difficult to construe, challenging researchers trying to date and reconstruct the tree of life. Before the present discovery, the oldest known red algae are 1.2 billion years old. By far the oldest plant-like fossils ever found, the Indian fossils, are 400 million years older. This suggests that the early branches of the tree of life need to be recalibrated.

Bengtson noted that it appears that the ‘time of visible life’ started much earlier than what was initially thought.

What is presumed to be red algae is embedded in fossil mats of cyanobacteria, called stromatolites, in 1.6 billion year old Indian phosphorite. The thread like forms were discovered first. Later, when the then doctoral student Therese Sallstedt investigated the stromatolites, the more complex, fleshy structures were discovered.

Sallstedt was so existed by the discovery that she had to walk three times around the building before going to her supervisor and telling him what she had seen.

The research group used a synchrotron-based X-ray tomographic microscopy to look inside the algae. The distinct and regular structures at the centre of each cell wall, typical of red algae, were clear to see among other things. Regularly recurring platelets were also observed in each cell. The team believes these are chloroplasts pieces. Chloroplasts are the organelles where photosynthesis takes place within plant cells.

The full peer reviewed study was published in the journal PLOS Biology.

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