May 26, 2017 0531 GMT
Ancient rocks from India suggest plants resembling red algae lived 1.6 billion years ago in what was then shallow sea, according to BBC.
The discovery may overturn ideas of when relatively advanced life evolved, said scientists in Sweden.
They identified parts of chloroplasts, structures within plant cells involved in photosynthesis.
The earliest signs of life on Earth are at least 3½ billion years old.
The first single-celled microscopic life forms evolved into larger multi-cellular eukaryotic organisms (made up of cells containing a nucleus and other structures within a membrane).
Therese Sallstedt of the Swedish Museum of Natural History discovered some of the fossils.
She described them as the oldest fossil plants that we know of on Earth in the form of 1.6 billion year old red algae.
She said, "They show us that advanced life in the form of eukaryotes (like plants, fungi and us humans/animals) have a much deeper history on Earth than what we previously have thought.”
Tree of life
The scientists found thread-like fossils and more complex ‘fleshy’ colonies in sedimentary rock from central India. Both have characteristics of modern red algae, a type of seaweed.
Co-researcher Professor Stefan Bengtson of the Swedish Museum of Natural History added: "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."
The oldest known red algae before the present discovery date back 1.2 billion years.
The Indian fossils are 400 million years older, suggesting that the early branches of the tree of life began much earlier than previously thought.
Claims of ancient life are always controversial. Without DNA evidence, confirmation must rest on whether more fossils can be found.
There is also debate over whether red algae belong in the plant kingdom or in a class of their own.
Modern red algae is perhaps best known for two commercial products — gelatinous texturing agents used in making ice cream — and nori — the seaweed used to wrap sushi.
The research was published in the journal, PLOS Biology.