Life forms that eventually gave rise to animals and plants may have appeared on Earth 400 million years earlier than previously believed. That’s the conclusion a team of scientists is making after discovering 1.6-billion-year-old fossilized cells in sedimentary rocks collected from central India. Based on their size, arrangement, and the presence of what appear to be fossilized subcellular structures (known as organelles), the cells appear to be early eukaryotes—the compartmentalized cells that make up all plants, animals, fungi, and everything else that isn’t a bacterium or single-celled microbe known as an archaeon. Experts previously believed the earliest eukaryotes evolved 1.2 billion years ago. The fossils appear to show two distinct types of red algae: Rafatazmia chitrakootensis (colored green in the rendering of R. chitrakootensis above), characterized as filamentous in shape and containing large rhomboidal disks that the researchers think may be parts of algal chloroplasts; and Ramathallus lobatus, which would have been more globular in shape and fleshier. Scientists already believed red algae to be some of the earliest eukaryotic organisms to evolve; pushing the date back further carries implications for our understanding of evolution as a whole and may help clear questions about the rates at which mutations occur in the genome over time. The researchers, who report their discovery today in PLOS Biology, caution that it’s impossible to be 100% sure they’re looking at red algae without DNA evidence, but any genetic material is long gone by this point.
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