Discovery Of Oldest Plants Could Rewrite When Complex Life Began On Earth

An X-ray false color (tomographic) picture of the fossil thread-like red algae. Stefan Bengtson; CCAL

 Scientists have discovered the oldest known plants on Earth in India – and it may push back the time we believe complex life first evolved on our planet.

In a study published in PLOS Biology, a team from the Swedish Museum of Natural History said they had found fossils of probable red algae that dated back 1.6 billion years. This is 400 million years older than previous red algae that has been found, and is by far the oldest plant-like fossils.

"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, Professor emeritus of palaeozoology at the Museum, said in a statement.

So, what is red algae? Well, it’s one of the oldest known types of eukaryotic algae – eukaryotes being single-celled or multicellular organisms with a nucleus and other organelles. Also called Rhodophyta, it’s red due to the presence of a pigment called phycoerythrin, and it’s important because it lets us look far back into Earth’s history.

"Red algae are the most primitive of the multicellular plants, and the appearance of plants on Earth is one of the most important events in the history of the biosphere," Bengtson told IFLScience. "Plants are crucial for the biosphere as we know it."

In this latest finding, scientists found two types of fossils resembling red algae in sedimentary rocks in Chitrakoot, India, specifically in fossil mats of cyanobacteria called stromatolites. One was thread-like, while the other was composed of “fleshy” colonies. The scientists saw distinct inner cell structures characteristic of red algae.

"I got so excited I had to walk three times around the building before I went to my supervisor to tell him what I had seen!" then doctoral student Therese Sallstedt said in the statement.

Life on Earth is thought to stretch back 3.5 billion years to single-celled organisms. Large multicellular eukaryotic organisms, so-called “visible life”, did not appear until 600 million years ago, just prior to the start of the Phanerozoic Eon when many animals began to evolve 541 million years ago.

With the previous oldest red algae dating back 1.2 billion years, this new finding pushes back the time when complex life is thought to have appeared on Earth (a study earlier this year suggested there may even have been two emergences of complex life). However, more fossils of this sort will need to be found before the claim can be verified.

"[This discovery] puts the clock back for major evolutionary events," Bengtson told IFLScience. "We shall probably have to reevaluate the timing of appearance of major lineages in the tree of life."

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