A quartz dyke at Hall's Creek, Australia, known as the China Wall. Credit: Graeme Churchard

Researchers in Germany have suggested that life on Earth may have begun underground. Ulrich Schreiber and Christian Mayer at the University of Duisburg-Essen say that their theory is the first that could explain how life developed from simple chemicals to enclosed cells (that is, with `membranes’ around them).

It’s not known just what conditions on Earth were like billions of years ago when life began. Until now, scientists have thought about the very first steps from the formation of simple to complex molecules and suggested this might have taken place at the Earth’s surface, deep underwater in the sea, by volcanoes or in shallow ponds. They’ve even thought about life arriving on Earth from space.

Ulrich Schreiber says people have overlooked the continental crust, that is, the rocks that form dry land on the continents and the relatively shallow seabed close to the shore.

`This region… offers the ideal conditions for the origin of life,’ Professor Schreiber says. He suggests that places where different regions (`plates’) of the earth’s crust meet can have a combination of water, carbon dioxide and other gases. These ingredients of life rise to the surface from deep underground, where the Earth is so hot that rock melts and is liquid instead of solid.

More than 800 meters underground, carbon dioxide, which is the gas in fizzy drinks, behaves as a `supercritical fluid’ – like a gas and like a liquid at the same time. It’s a great place for chemicals to interact and form simple and complex molecules needed by life. It also interacts with water to form membranes that are needed for living cells.

Professor Schreiber and another Duisburg-Essen colleague, Oliver Schmitz, have collected and are analysing rock samples from places where quartz filled the cracks of the crust, such as at `quartz dykes’ in western Australia. They hope to find further evidence to support their hypothesis when they know more about the chemicals in the rocks.