The Martian meteorite ALH84001
The account
A rock from Mars carried fossils of microbes, the first proof of life beyond Earth.
What investigators found
The structures that looked like fossils may have formed without life. Most scientists today do not consider them proof, but the debate paved the way for the search for life on Mars.
The story
In 1984, researchers found in the Allan Hills of Antarctica a meteorite about 4 billion years old that was later found to have come from Mars. In August 1996, a NASA team announced that it contained microscopic structures resembling fossilized bacteria.
The announcement stopped the world, and even the President of the United States spoke about the discovery. In the years that followed, other studies showed that similar shapes can form through chemical processes without life. Today most scientists do not accept the rock as proof, but it changed the exploration of Mars, which made the search for life a priority.