The United Nations has launched a project to unravel the mysteries of the biggest source of untapped life on earth, the plants and animals living just below ground level.

The $26 million project will try, over the next five years, to discover thousands, and possibly millions of previously unknown life forms in the thin outer crust of the earth.

Scientists are optimistic that the discovery of new species of bacteria, fungi, insects and worms will lead to new drugs, industrial applications and more eco-friendly farming techniques.

The technical adviser to the project is Jo Anderson of Britain's Exeter University. He compares the study with other great scientific adventures. "I grabbed this bagful of soil from just outside my house before I came up," he said. "There is probably greater biological diversity in that bag than there are plants and animals in a tropical rainforest. While we are thinking of the exploration of the deep sea, and the tremendous excitement about the exploration of the deep sea - we are also very interested in life on Mars - right beneath our feet is one of the last scientific frontiers to be cracked."

The study will be carried out in seven countries in Africa, Asia and Latin America. They are Brazil, Mexico, Ivory Coast, Uganda, Kenya, Indonesia and India.

Scientists leading the project say earlier studies are already reaping important gains.

Fatima Moriera of Brazil says bacteria that can put nitrogen from the air back into the soil are now saving her country $1 billion a year that used to be spent on chemical fertilizers to grow soybeans.

Patrick Lavelle of the University of Paris says India has been able to triple production at degraded tea plantations by introducing large numbers of earthworms into the soil.

Other potential applications scientists will be pursuing include using bacteria to devour spilled oil, and finding micro-organisms that can help farmers reduce the amount of water, pesticides and plowing they now use in food production.