Earlier this week, researchers from the Swedish Museum of Natural History made a spectacular claim, announcing that they may have found 1.6-billion-year-old photosynthetic algae. If confirmed, the fossils would be 400 million years older than any other plant-like multi-cellular life ever discovered. The researchers published the find in the journal PLOS Biology.
The fossils were discovered in sedimentary rock found in Chitrakoot, an area in the state of Uttar Pradesh in north central India. According to Erin Ross at Nature, the researchers discovered three types of fossils that resemble red algae while studying a series of stromatalites—fossilized mats of blue-green algae that are likely among the oldest life on earth.
One of the algae fossils looks like round and fleshy plates arranged like a stack of coins. It is similar to modern colonial bacterium and the researchers are calling it Denaricion mendax. The other two are long filaments separated into chambers that the researchers are calling Rafatazmia chitrakootensis and Ramathallus lobatus.
Using synchrotron-based X-ray tomographic microscopy the team was able to peek inside the fossils, which contain structures similar to those found in red algae. The team identified platelets within the fossils that they believe were parts of chloroplasts, an organelle in plants where photosynthesis takes place.
“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 paleozoology at the Swedish Museum of Natural History and lead author of the paper says in a press release.
As George Dvorsky reports for Gizmodo, prior to this find, the oldest-known complex multicellular organism was Bangiomorpha pubescens, a type of fossilized red algae discovered on Somserset Island in the Canadian arctic dated to 1.2 billion years. A recent study suggests that single-cellular life arose on earth some 3.77 billion years ago, shortly after the planet was formed. And those life forms dominated the planet for around 2.5 billion years, notes Dvorsky. But sometime between 2.1 and 2.7 billion years ago, those cells merged, creating eukaryotic organisms—creatures with complex cells that contain a central command center or nucleus.
But how did it happen? "The world's lush profusion of photosynthesizers — from towering redwoods to ubiquitous diatoms — owe their existence to a tiny alga eons ago that swallowed a cyanobacteria and turned it into an internal solar power plant," David Biello wrote for Scientific American in 2012.
These fossils could help pin down when this switch occurred, Debashish Bhattacharya, an evolutionary biologist at Rutgers University tells Ross. Bhattacharya believes the new fossils do represent species of red algae, but thinks it is more likely that these fossils belong to "very ancient side branch," writes Ross.
Others, however, are skeptical about the claim. Paleobiologist Nicholas Butterfield from the University of Cambridge, who first identified Bangiomorpha, tells Ross that he’s not convinced the fossil is red algae—or even a eukaryote at all. He points out that while the new fossils do share some characteristics with red algae, the presence of internal platelets are not enough to convince him. Many of the tiny organisms that lived billions of years ago are superficially similar, he says, and hard to tell apart.
“That’s the problem with this field,” Butterfield says. “You stand back and squint, and say ‘well, the fossil kind of looks like X.’”
Regardless of what the fossils actually are, one of the big takeaways of the research is the potential of the new imaging techniques, paleobiologist Glenn Brock from Macquarie University in Australia tells Bianca Nogrady at the Australian Broadcasting Corporation. “When we start using some of these techniques to look at slightly older or at least equivalent aged fossils, we might start to see that these things are more common than we previously thought, mainly because we can now look at them in a brand new way,” he says.
It's unlikely that these fossils will be the last word on when complex life arose, he says. Who knows? Researchers soon could discover other fossils that push that date back even further.