Martian Fossils on Earth?

How can we tell that meteorite ALH 84001 comes from Mars, and what is it doing on Earth?! This meteorite, found in Antarctica in 1984, provided scientists with evidence suggesting the possibility that life once existed on Mars. Dr. Fred Bortz uses the scientific process to break down what we know, and what we are still learning. Newly updated (2014) to include data acquired by the Spirit, Opportunity and Curiosity rovers.