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

In a paper last month in the journal Nature, an international team of scientists sought to sort this out for a particular group of meteorites known as shergottites. Martian space rocks tend to be very old, but shergottites are thought to be remarkably young.

Formed When Dinosaurs Roamed Earth

###### This would place their formation during Earth's Jurassic period, when dinosaurs roamed the Earth.

If so, shergottites are a sign that Mars might have been geologically active fairly recently. That in turn means it might still have been hospitable to some form of life, said Munir Humayun, a planetary geochemist at Florida State University who was not involved in the study. ###### Most of us understand that if there is to be life on Mars, it's not going to be roaming on the surface. ... but it could be thriving underground with the heat energy provided by volcanism," Humayun said.

However, "if there hasn't been [volcanic activity in] 4 billion years, ... it would be very difficult to believe there was life left on Mars."

To settle the question, Desmond Moser of Western University in Ontario, Canada had his team examine a meteorite known as Northwest Africa 5298. ###### These tough, zirconium-rich minerals 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.

A Tough Tiny Mineral In Meteorites

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. But that isotopic ratio can be reset by a big impact that melts the rock down, erasing the geochemical trail. ###### It's not easy to melt them down and reset their isotopic clock. By looking at the isotopic ratios of radioactive uranium and lead in this tough rock, the scientists found that it formed about 187 million years ago, give or take 33 million years. This confirmed that the baddeleyites were young. ###### The shock from that impact muddled up the mineral structure inside, while keeping the chemicals themselves mostly intact.]]>