24 Dec 2008

Scientists say life began in two bursts

8:03 am on 24 December 2008

Scientists in the United States say they have discovered that much of the evolution of life on Earth took place in two distinct surges.

The first great increase in size and complexity came two billion years ago, when single-celled organisms developed cell membranes.

The second happened 540 million years ago, when multi-cellular creatures first appeared.

The research also shows both those evolutionary jumps coincided with big increases in oxygen in the Earth's atmosphere.