Fossils mark a key moment in evolution when bacteria started to become more complex cells capable of photosynthesis and sexual reproduction
Fossils of some of the first life forms to make the pivotal jump from the oceans to land have been found on the edge of a remote Scottish loch.
Rocks around Loch Torridon, on Scotland's west coast, contain the preserved remains of organisms that once lived at the bottom of lakes a billion years ago.
They mark a key moment in evolution when simple bacteria started to become more complex collections of cells capable of photosynthesis and sexual reproduction.
One of the primitive life fossils found at Loch Torridon on Scotland's west coast. They contain the preserved remains of organisms that once lived at the bottom of lakes a billion years ago
Professor Martin Brasier, from Oxford University's Department of Earth Sciences, said: 'These new fossils show that the move toward complex algal cells living in lakes on land had started over a billion years ago, much earlier than had been thought.'
His research is reported in the journal Nature.
Unlike their bacterial ancestors, the cells had specialised structures including a nucleus, as well as machinery vital for photosynthesis.
They also reproduced sexually, which helped to speed up evolution.
Experts believe the organisms ultimately gave rise to green algae and land plants.
Co-author Dr Charles Wellman, from the University of Sheffield, said: 'It is generally considered that life originated in the ocean and that the important developments in the early evolution of life took place in the marine environment.
Loch Torridon: The fossils are of some of the first life forms to make the pivotal jump from the oceans to land'During this time the continents are often considered to have been essentially barren of life - or at the most with an insignificant microbial biota dominated by cyanobacteria.
'We have discovered evidence for complex life on land from one-billion-year-old deposits from Scotland.
'This suggests that life on land at this time was more abundant and complex than anticipated.
'It also opens the intriguing possibility that some of the major events in the early history of life may have taken place on land and not entirely within the marine realm.'
Around 500million years after the appearance of the life forms, the land surface began to be colonised by simple vegetation such as lichens, mosses and liverworts, said the scientists.
At about the same time the first simple animal organisms began to migrate out of the sea.
They were followed by the emergence of fish, reptiles, mammals, ferns, conifers and flowering plants.
Professor Brasier added: 'None of this would have been possible without advances long ago made by these little microbes, now entombed within phosphate from the Torridon lakes.
'It was arguably these organisms that helped to turn our landscape from a harsh and rocky desert into a green and pleasant place.'