Mars life? 20 years later, debate over meteorite continues

Twenty years ago, NASA scientists and their colleagues announced they had spotted possible signs of Mars life in a meteorite. The claim ignited a scientific controversy that lingers to this day.

In 1996, researchers led by David McKay, Everett Gibson and Kathie Thomas-Keprta from NASA's Johnson Space Center in Houston suggested that they might have found microbial fossils in a meteorite from Mars known as Allan Hills 84001 (ALH 84001). (Cosmic impacts on Mars can be powerful enough to blast rocks off the Red Planet, a fraction of which crash on Earth, the moon and other bodies in the solar system.)

The meteorite was first discovered in 1984 by geologists riding snowmobiles through the Allan Hills region of Antarctica. Scientists think ALH 84001 originally formed 4 billion years ago on Mars and landed on Earth about 13,000 years ago.

In the study, which appeared in the Aug. 6, 1996, issue of the prestigious journal Science, McKay and his team presented four lines of evidence that ALH 84001 might have harbored alien life. One of the strongest was the existence of microscopic magnetite crystals that the researchers said bore remarkable similarities to ones created by microbes on Earth.

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