Mathematics research at the Australian National University could help answer big questions about the origin of life on Earth.

Murray Batchelor, of the Mathematical Sciences Institute, is modelling the formation of stromatolites, rocks built in shallow water by photosynthetic micro-organisms.

The rocks are among the earliest signs of life on the planet, and some of the oldest putative specimens - dated to more than 3 billion years old - are in Western Australia's Pilbara region.

Stromatolites are still forming in Western Australia's Shark Bay, a World Heritage-listed site and one of the few relics of the dawning of life on Earth.

However, debate rages over whether ancient specimens in the geological record have biological or chemical origins. The shape of the structures is central to the argument. Some are dome-shaped while others are conical. Still others have branching structures like coral.

"The big puzzle is why the various shapes arose," says Batchelor. "Was it a response to some change in the environment?"

His team has developed a mathematical model to simulate stromatolite growth patterns to see if biological processes alone account for the shapes.

One parameter in the model is sensitivity to light. "Stromatolites grow in a community of microbes," says Batchelor. "They respond to light, so they grow upwards."

Another parameter relates to the precipitation of calcium carbonate from the water by the microbes, one of the main mechanisms of the formation of the rocks.

The work, in collaboration with Robert Burne, of the ANU's Research School of Earth Sciences, has taken the mathematicians on fields trips to Western Australia.

The research could help in the conservation of the delicate Shark Bay ecosystem. "We need to learn more about the way stromatolites grow."