While little bits of a compound called magnetite look very much like the ones found in some bacteria, the ones in the meteorite were formed inside the rock as the result of heat, not life, said Ed Scott, of the university's Hawai'i Institute of Geophysics and Planetology.

The meteorite, found in Antarctica in 1984, probably landed on Earth 13,000 years ago, having been driven off the Martian landscape by an impact by another object. When researchers studied it, they found what appeared to be tantalizing clues suggesting that life might once have existed on Mars.

The evidence excited the world of science, since it provided the first possible hard evidence of life outside Earth. But the finding was controversial from the first.

Scott and British researcher David Barber, of the University of Greenwich, believe their research puts the issue to rest.

Their research will be reported tomorrow in the Proceedings of the National Academy of Sciences.

Researchers in 1986 reported they saw tiny crystals of magnetite ­ a compound containing iron and oxygen ­ with shapes that matched those found in bacteria on Earth. Bacteria form the magnetite within their cells, and to use it to help them navigate. Magnetite aligns itself with the Earth's magnetic field, just as a magnetized compass needle points north.