Building blocks of life found, 2.1bn years on

THEY are as small as a thumbnail, but show that life as we know it has existed for hundreds of millions of years longer than previously thought.

In a development that will rewrite the origins of organised life, scientists have discovered the oldest fossils of a multi- cellular organism.

The west African specimens, which lived in shallow water around 2.1 billion years ago, are the earliest examples of lifeforms that had their own DNA.

Shaped like biscuits, the specimens are 200 million years older than for any previous claim and have been described by researchers as a "remarkable" find.

The ancient macrofossils were discovered near Franceville in Gabon two years ago.

After analysing their structure and chemical content, it emerged the specimens were not rock formations, but the remains of living organisms.

The first traces of life were simple "prokaryotic" organisms, which appeared 3.5 billion years ago, while 600 million years ago the Earth underwent The Cambrian Explosion - where oxygen levels in the atmosphere soared alongside a huge proliferation in the numbers of different species of life.

Researchers are thrilled by the Gabon discovery because they feel it is vital to find out what happened between the arrival of prokarytic life and the Cambrian Explosion. During the so-called Proterozoic era life on Earth diversified, setting the scene for the emergence of complex plants and animals.

The breakthrough, published in the journal Nature, was made by a team led by Dr Abderrazak El Albani from the University of Poitiers, France.

Dr Elbani said: "The evolution of the Gabon macrofossils, representing an early step toward large-sized multicellularity, may have become possible by the first boost in oxygen, whereas the Cambrian Explosion could have been fuelled by the second. Why it took 1.5 billion years for the multicellular organisms to take over is currently one of the great unsolved mysteries in the history of the biosphere."

During the Proterozoic era a new type of life called eukaryotes developed alongside prokaryotes, and were the first organisms with a more complex structure and metabolism, including cell nuclei - where DNA is stored.

Around 100 of the 250 samples, which are a variety of shapes and sizes and are up to 6in long, have been studied. They lived in colonies, with as much as 40 in a half square metre being dug up, in a shallow marine environment down about 100ft.

Dr Philip Donoghue from the University of Bristol's department of earth sciences said: "Normally, to find fossils from this time you need to dissolve rocks and look under a microscope. These aren't aggregations of bacteria. They're three-dimensional, which suggests co-ordinated multicellularity."

However, Dr Donoghue cautioned against describing the fossils as the building blocks for modern life.

"Even if these fossils are the oldest-known multicellular organisms, that doesn't mean they were the ancestors of all multicellular life. Multicellularity hasn't evolved just once; it's evolved almost 20 times even amongst living lineages."