Billion-year-old seaweed fossil suggests algae is 200 million years older than we previously thought

Scientists believe the billion-year-old green algae could be related to the ancestor of the earliest land plants and trees that first developed 450 million years ago.

  • Ancient seaweed believed to be around one billion years old.
  • Fossil discovered in rock taken from an area of dry land in northern China.
  • The finding suggests green algae is 200 million years older than previously thought.
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One-billion-year-old seaweed fossils are believed to be the oldest green algae discovered.

They could also be related to the ancestor of the earliest land plants and trees that first developed 450 million years ago, researchers say.

The micro-fossil seaweeds, a form of algae known as Proterocladus antiquus, are hardly visible to the naked eye, at 2mm in length.

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The specimens were imprinted in rock taken from an area of dry land near the city of Dalian in the Liaoning Province of northern China, which used to be ocean.

Before the discovery, published in the Nature Ecology and Evolution journal, the earliest convincing fossil records of green seaweeds were found in rock dated at about 800 million years old.

A photo of a green seaweed fossil dating back 1 billion years. The image was captured using a microscope as the fossil itself is 2 millimeters long, roughly the size of a flea. The dark color of this fossil was created by adding a drop of mineral oil to the rock in which it's embedded, to create contrast © Virginia Tech
The seaweed fossil is believed to be one billion years © Virginia Tech

Professor Shuhai Xiao of Virginia Tech university in the US, said: “These new fossils suggest that green seaweeds were important players in the ocean long before their land-plant descendants moved and took control of dry land.

“The entire biosphere is largely dependent on plants and algae for food and oxygen, yet land plants did not evolve until about 450 million years ago.

“Our study shows that green seaweeds evolved no later than one billion years ago, pushing back the record of green seaweeds by about 200 million years.”

He added that the current hypothesis is that land plants like trees, grasses and food crops, evolved from green seaweeds – aquatic plants.

“These fossils are related to the ancestors of all the modern land plants we see today,” Prof Xiao said.

The background shows ancient microscopic green seaweed living in the ocean, while the foreground shows the seaweed being fossilised © Dinghua Yang/PA
The background shows ancient microscopic green seaweed living in the ocean, while the foreground shows the seaweed being fossilised © Dinghua Yang/PA

However, not all geobiologists agree on the origins of green plants, with some suggesting they started in rivers and lakes, before conquering the ocean.

The researchers suggest the tiny seaweeds once lived in a shallow ocean, died and then became “cooked” under a thick pile of sediment, preserving their shape.

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According to the scientists, the seaweeds’ multiple branches, upright growth and specialised cells suggest the fossil is a green seaweed that is about one billion years old.

Reader Q&A: Which came first, the plant or the seed?

Asked by: Adam King, Huddersfield

The earliest fossils of complex land plants date from around 470 million years ago. They resembled liverworts – a kind of simple moss – and reproduced by releasing spores, which were carried away when it rained.

Spores contain a single cell, whereas a seed contains a multicellular, fertilised embryo that is protected from drying out by a tough coat. These extra features took another 150 million years to evolve, whereupon the first seed-bearing plants emerged. So plants came first, by a long way.

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