Martian rocks photographed by the robotic Spirit rover in 2006 as it rolled across Mars. Photo: Mars Exploration Rover Mission, Cornell, JPL, NASA

###### They looked at very tiny deposits within it known as baddeleyites - tough, zirconium-rich minerals that are "10 times smaller than the diameter of a human hair," said study co-author Axel Schmitt, a geochemist at the University of California, Los Angeles.

Researchers generally measure relative amounts of pairs of radioactive elements in rocks to gauge how long a rock has been around since it fully crystallized. ######

That's why scientists picked the tiny baddeleyites: Once they form, they are resilient little minerals. It's not easy to melt them down and reset their isotopic clock. ###### This confirmed that the baddeleyites were young.

The scientists could also see evidence of the damage done to the meteorite by the event that may have released it from the Martian surface about 22 million years ago (give or take 2 million). ######

"It looks good on the outside, but all the pieces are dislodged on the inside," Schmitt said. The study further shows that the shergottites weren't old rocks, Humayun said - although he also called the argument that they were ancient a "straw man that's been set up that everybody's trying to take down." ######

The researchers say they can use their method of dating these rocks to study the other Martian meteorites in Earthly possession, and see if it reveals new information about the Red Planet's geophysical inner life.]]>