amenable to some form of life, said Munir Humayun, a planetary geochemist at Florida State University who was not involved in the study.]]> gauge how long a rock has been around since it fully crystallized.]]> Conflicting age estimates for certain rocks differ by up to 4 billion years - the vast majority of Mars' planetary existence.]]> intact - like shaking up a sealed gift box of chocolates.]]> existence.]]> differ by up to 4 billion years - the vast majority of Mars' planetary existence.]]> dislodged on the inside," Schmitt said.]]> hurtling through space and surviving the searing fall through our atmosphere.]]> interpret what they see when they can't agree how old a rock is.]]> impact that melts the rock down, erasing the geochemical trail.]]> diameter of a human hair," said study co-author Axel Schmitt, a geochemist at University of California, Los Angeles.]]> thriving underground with the heat energy provided by volcanism," Humayun said.]]> meteorite known as Northwest Africa 5298.]]> atmosphere.]]> examined a meteorite known as Northwest Africa 5298.]]>