The history of life on Earth is shrouded in shadow, but we're slowly shedding more light on where we came from. Now, newly-discovered fossils of what look like red algae discovered in Chitrakoot, India, suggest that multicellular life arose several hundred million years earlier than previously believed.

Life can be traced as far back as 3.7 billion years (and arguably, even earlier), preserved in "mats" of fossilized single-celled microbes known as stromatolites, but it took much longer for multicellular forms of life, called eukaryotes, to emerge. While the fossil record is still spotty in regards to when this more advanced life evolved, they appear to have been fairly common by the Phanerozoic Eon (which translates to "the time of visible life"), beginning around 540 million years ago.

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Discovered by scientists from the Swedish Museum of Natural History, the new fossils provide a clearer window into when advanced life began to form. Two types of fossils were found in stromatolites of cyanobacteria: one with a structure like thread, and the other with a more fleshy form. They closely resemble red algae, yet are 400 million years older than the previously earliest known examples of red algae, making them the oldest plant-like fossils by a wide margin.

"You cannot be 100 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," says Stefan Bengtson, lead author of the study. "The 'time of visible life' seems to have begun much earlier than we thought."

The researchers studied the algae using X-ray tomographic microscopy, which allowed them to spot key characteristics. Inside the cells, the team has spotted platelets that appear to be part of the structures responsible for photosynthesis, and the cell walls have distinctly red algae-like structures to them. The cells themselves were arranged in a sprawling pattern called "cell fountains," which are also regularly seen in red algae.

The discovery pushes back the clock for when multicellular life began to take shape, and the researchers say the early branches of the "tree of life" may now need a little rearranging.

The research was published in the journal PLOS Biology.

Source: PLOS via Science Daily