Ancient lakes show when eukaryotic life left the sea

18:00 13 April 2011 by Colin Barras

Pools of water on land were a lot livelier 1 billion years ago than previously thought.

It is generally assumed that life began in the ocean around 3.8 billion years ago, then moved onto land. Until now, there had been little evidence to suggest this landward migration happened before half a billion years ago. The discovery of eukaryote cells in 1-billion-year-old lake sediment looks set to change that.

Paul Strother at Boston College in Weston, Massachusetts, and colleagues discovered cyst-like bubbles made of organic matter in 1 to 1.2-billion-year-old lake deposits. The bubbles were packed full of fossilised cells, and found in a number of locations across the north-west of Scotland, UK.

Strother says the cells, which appear to be going through vegetative reproduction, show a level of structural complexity "beyond that seen in bacteria" but characteristic of eukaryotes – one of the three domains of life. This suggests the primitive relatives of all animals, plants and fungi had left the oceans and moved into terrestrial waters twice as long ago as thought.

Non-marine sediment

Palaeontologists contacted by New Scientist for comment agreed. "They most certainly appear to be eukaryotic, and the non-marine nature of the encompassing sediments seems well established," says Andrew Knoll at Harvard University. "Previous to this, the oldest clearly non-marine eukaryotes may have been [roughly 540-million-year-old] Cambrian spores."

Emmanuelle Javaux at the University of Liège, Belgium, calls it "a significant discovery". The age of the rocks puts them "near the beginning of diversification of eukaryotic supergroups, and is an important new element for improving our understanding of early terrestrialisation processes in general – and evolution of the eukaryotes in particular."

Eukaryotes may not have been the sole colonisers of land at the time. There is also evidence that cyanobacteria – some of the earliest known forms of life – evolved first in fresh water, before moving to the ocean.

Journal reference: Nature, DOI: 10.1038/nature09943

http://www.newscientist.com/article/dn20373-ancient-lakes-show-when-eukaryotic-life-left-the-sea.html