Do these rocks tell the beginning, or the end, of Mars' story?

###### a paper last month in the ###### Nature, an international team of scientists ###### to sort out this issue for ###### particular group of meteorites known as ######. Martian space rocks tend to be ###### old, but shergottites are generally thought ###### be remarkably young- forming as a ###### of volcanic activity about 150 million ###### 250 million years ago, around the ###### time that dinosaurs roamed during Earth's ###### period.
If so, shergottites are a ###### that Mars might have been geologically ###### fairly recently, and thus perhaps still ###### to some form of life, said ###### Humayun, a planetary geochemist at Florida ###### University who was not involved in ###### study.]]> Researchers ###### measure relative amounts of pairs of ###### elements in rocks to gauge how ###### a rock has been around since ###### fully crystallized. But that isotopic ratio ###### be reset by a big impact ###### melts the rock down, erasing the ###### trail.
That's why scientists picked the ###### baddeleyites: Once they form, they are ###### little minerals.]]>