WIDESPREAD outcrops on Mars of a green rock called olivine suggest the planet
has long been too dry and cold for life to flourish on its surface.
A blend of iron and magnesium silicates, olivine is found inside some
volcanic deposits on Earth, but it doesn’t last long once it has been exposed.
In warm, moist environments it starts weathering in months, says Roger Clark of
the US Geological Survey in Boulder, Colorado. Yet spectroscopic data shows that
olivine covers over 2.5 million square kilometres on Mars, including some
ancient regions that are heavily cratered or eroded, he told a…
