Over time, astronomers were able to identify more of these so-called Martian meteorites. And they began to seriously scrutinize them. In 1996, a team of NASA scientists shocked the world when they reported that they had found fossils of Martian bacteria in a meteorite known as ALH84001.
The ALH84001 meteorite, which was unearthed in the Allan Hills area of Antarctica in 1984, contained yellowish grains of carbonate, a common mineral that can have biologic origins. When the scientists studied the carbonate under an electron microscope, they saw rodlike structures that they said were fossilized bacteria cells. They also detected iron sulfides and magnetite, two compounds synthesized simultaneously by certain bacteria. The research team hypothesized that the bacteria formed on Mars and traveled to Earth as passengers aboard ALH84001.
Since then, several studies have shown that the chemical compounds in ALH84001 likely formed without the influence of any life processes and therefore don't prove the existence of Martian life. But the question has never been conclusively answered one way or the other. As a result, interest in Martian meteorites remains high, and scientists and rock hounds scour the globe to find new specimens.
They also study previously collected specimens to see if any should be reclassified. Of the 53,000 meteorites that we've officially cataloged on Earth, 104 have been labeled Martian [source: Marlow]. Eyewitnesses have only seen five of these rare rocks arrive on our planet. The rest made a quiet entry and were found after their impact, often in Antarctica or North Africa because they're easy to spot on ice or sand.