Martian rocks photographed by the robotic Spirit rover in 2006 as it rolled across Mars. Photo: Mars Exploration Rover Mission, Cornell, JPL, NASA
Most Martian space rocks are very old. But shergottites are believed to be very young. ###### Most scientists believe shergottites were formed by volcanoes about 150 to 250 million years ago. That was during Earth's Jurassic period. Dinosaurs roamed our planet then.

If they are right, then Mars had volcanoes not too long ago. ###### But some people believe that shergottites are actually very old - about 4 billion years old. If this is true, other scientists will have to change the way they think about life on Mars.

Tiny, But Tough

"If there is ... life on Mars, it's not going to be roaming on the surface. ... but it could be thriving underground with the heat ... provided by [volcanoes]," Humayun said. However, "if there [haven't been volcanoes in] 4 billion years, ... it would be very difficult to believe there was life left on Mars."

###### They looked at very tiny minerals within it called baddeleyites. These tough minerals are "10 times smaller than ... a human hair," said scientist Axel Schmitt.

To figure out how old a rock is, scientists measure certain parts inside it. But sometimes a big crash or explosion melts the rock down. ###### That's why scientists picked the tiny baddeleyites: They are hard little minerals. It's not easy to melt them down. By looking at the uranium and lead inside this tough rock, the scientists found that it formed sometime around 187 million years ago. This proved that the baddeleyites were young.

New Discoveries Ahead?

###### The shock had muddled up the minerals inside.

The result was something like shaking up a sealed box of chocolates.]]>