Millions of years ago, an object hit the surface of Mars so hard that pieces of it flew up and escaped the planet's gravity. One piece was pulled down by Earth's gravity and was discovered in Antarctica. Scientists named it ALH84001. At first, they thought this meteorite contained traces of tiny bacteria. This would have proved that life existed on Mars. After further study, scientists decided that the bacteria may have entered the meteorite on Earth instead. The scientists their findings.