Researchers solve Martian meteorite age conundrum

Dr James Darling

The discovery that Martian meteorites are four billion years younger than previously suggested means that Mars could still be geologically active

In a paper published today in the journal Nature, a team of researchers show that a meteorite from the Mars collection at the Royal Ontario Museum in Canada started as a 200 million year old lava flow on Mars.

This finding is significant because it paints a much clearer picture of the red planet’s geological history. It shows that if volcanoes on Mars were active 200 million years ago, there is a possibility it could still be an active planet, and if it isn’t, that it was geologically active much more recently than thought.

The team of scientists from the University of Portsmouth, the Royal Ontario Museum, the University of Wyoming and the University of California, Los Angeles used a new technique to determine the age of the rocks, by directing energy beams at tiny crystals found inside them.

They also discovered crystals that grew while the meteorite was launched from Mars towards Earth, allowing them to narrow down the time it left Mars to less than 20 million years ago.

University of Portsmouth scientist, Dr James Darling, from the School of Earth and Environmental Sciences, said: “There has been a long debate about the actual age of precious Martian rocks that have been found on Earth. Some scientists suggested they were formed as part of the ancient Martian crust and are therefore around 4000 million years old – almost as old as the Solar System itself. And others believed they were much younger.

“The meteorites found on Earth have been ejected from Mars, probably after being dislodged by a large meteorite impact, and have eventually been hoovered up by Earth. This process causes extensive damage to the samples, including deformation and melting of the crystals that make up the rock.

“The real challenge has been interpreting whether the measured age of the rock is the time at which it was formed or the time at which it was ejected from the Martian surface.”

The team used a number of high resolution techniques to analyse the Martian crystals, examining samples far smaller than a human hair. The researchers combined isotopic analysis with micro-structural analysis, which means they looked at both the structure of the crystals and the chemistry in order to determine the growth history of the crystals.

“This is a really exciting study,” said Dr Darling, “not only because it gives us a much better understanding of the geological activity on Mars, but also because we can apply this new technique to meteorites from the Moon and other asteroids, which means we can start to analyse hundreds of rocks from the Solar System.”

Nearly 100 meteorites found on Earth are thought to be from Mars. They are kept in collections all over the world and are hugely valuable scientifically as they provide researchers with unique insights into the history of the ‘Red Planet’. The scientists analysed a ‘shergottite’ meteorite found in North Africa, which is kept at the Royal Ontario Museum.

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