Man may have discovered fire a million years earlier than scientists thought, according to reports from a new excavation in Africa.

A team of one American, one Canadian and two British anthropologists discovered the site in Kenya, where stone tools and 40 fragments of baked clay in a patch of earth dated from 1,420,000 years ago.

Until now, the best evidence for man's use of fire was found at sites dated at 500,000 years old. The first use of fire is a major marker of the beginning of humanity, since other animals have used tools but only man has mastered fire.

The discovery came in excavations in Chesowanja, Kenya. The baked clay stones were found clustered in a 20-foot section of trench, which also held animal bones and tools of the kind associated with Homo erectus, believed to be the precursor of Homo sapiens, modern man.

According to the current issue of the British journal Nature, tests showed that the small bits of burnt clay were subjected to temperatures of about 400 degrees Celsius -- about normal for an open campfire. If that temperature were sustained for hours it could bake and harden clay. But if the clay were burned and hardened by a natural fire in the bush, the clay should have evidence of heat at 700 degrees for a very short time, usually not enough to harden clay into stones.

The report in Nature was made by J. W. Harris of the University of Wisconsin, Derek Walton of McMaster University in Canada, J.A. Gowlett of Oxford University, and B. A. Wood of Middlesex Hospital School in London.

They wrote that although "natural phenomena such as bush fires, lightning strikes and even volcanic heating could explain the burnt clay at Chesowanja, we are convinced, from examination of the whole occurrence [at the site] that hominid activity is a much more likely explanation."