Could we ever know whether life on Mars represents a second genesis?

If we are ever successful in finding life on Mars, one of the key questions we would want to answer is whether life on Mars formed independently or shared a common origin with life on Earth. The issue arises because we know that it is possible for material to be transferred between the two planets. We know of more than 20 meteorites that originated from Mars. Indeed, it was suggested in 1996 that there was evidence for fossil life in the Martian meteorite ALH84001. While the evidence for life in ALH84001 has not been generally accepted, studies of the meteorite have shown that it travelled from Mars to Earth without its interior being heated to more than 40°C. It has also been demonstrated that bacterial spores can survive in space for more than 5 years.