Seaweed-like fossils found in rocks in China dated to around 1.56 billion years ago are the earliest known examples of larger organisms made up of many cells built like our own.

Key points: 167 fossils discovered in 1.56 billion year old rock are up to 30 centimetres long and eight centimetres wide

167 fossils discovered in 1.56 billion year old rock are up to 30 centimetres long and eight centimetres wide Until now, fossils of multicellular life of this size weren't seen in the fossil record until 600 million year ago

Until now, fossils of multicellular life of this size weren't seen in the fossil record until 600 million year ago Shape of fossils suggest organisms were photosynthetic

The discovery, reported today in Nature Communications, places the organisms in the middle of what had previously been known as the 'boring billion' period in the evolutionary history of life on Earth.

The fossils, which are up to 30 centimetres long and nearly eight centimetres wide, were found in northern China.

The cells show distinctive features suggesting they are eukaryotes; that is, they have an enclosed nucleus like ours.

Co-author Dr Maoyan Zhu from the Nanjing Institute of Geology and Palaeontology said until now, the earliest known examples of multicellular life of this size weren't seen in the fossil record until around 600 million years ago, in a period of time just before the rapid emergence of complex life in the so-called Cambrian explosion.

As the name suggests, the fossil record before this known as the 'boring billion' was characterised by much less exciting microscopic forms of life, said Dr Zhu.

"People will be rethinking this time, the Mesoproterozoic," he said.

Fossil shape hints at photosynthesis

Rock showing impression of tongue-like fossil (right hand side of image) ( Maoyan Zhu )

The 167 fossils come in a variety of shapes and sizes but many have a distinctive leaf shape — some tapered at both ends, others rounded or tongue-shaped.

Co-author and palaeontologist Professor Andrew Knoll from Harvard University said these large multicellular eukaryotic forms appear not long after the emergence of the very first eukaryotic cells.

What are eukaryotes? Eukaryotes is a group of organisms made up of cells that have a nucleus that contains genetic material bound in a defined membrane.

Eukaryotes is a group of organisms made up of cells that have a nucleus that contains genetic material bound in a defined membrane. They can be singled-celled or multi-celled organisms

They can be singled-celled or multi-celled organisms Animals, plants, fungi and algae are eukaryotes

"We know that eukaryotic cells — cells with membrane-bound nucleus like our own — the first time we see them is between [1.8 -1.6 billion] years ago," said Professor Knoll.

While the fact that single-celled organisms had organised so quickly into multicellular forms wasn't itself that remarkable, the shape of these fossils did suggest the possibility of photosynthesis, he said.

"If you look at blade-shaped organisms like this today, things that are leaf-like or seaweed-like ... almost everything that has that shape is photosynthetic, so this suggests that photosynthesis came to the eukaryotes fairly early in their history as well."

Another piece to the puzzle of early life

Commenting on the study, Professor Simon George said it added another piece to the puzzle of early life on Earth and confirmed earlier chemical evidence of eukaryotic life.

"We've got chemical evidence that the evolution of eukaryotes goes quite a bit further back than the earliest fossils we see and this is quite a common thing when you are comparing paleobiology and fossils with other evidence," said Professor George, professor of organic geochemistry at Macquarie University.

"So finding a location like this with these very large fossils is starting to shed light more definitively on the sorts of eukaryotes that existed and they are a lot bigger than what we had previously thought."

Professor George said these fossils were highly likely to be of multicellular eukaryotic organisms rather than large mats of single-celled microbes without a nucleus.

"You wouldn't expect chunks of a microbial mat, if it was ripped up, which can happen in waves, it wouldn't end up looking like this, with this fairly consistent morphology and also with these cells which do seem nicely distributed and clearly showing that it's got carbon in it."