Dating planetary surfaces
Farley and his colleagues determined the age of the mudstone to be about 3.86 to 4.56 billion years old.
"In one sense, this is an utterly surprising result—it's the number that everybody expected," Farley says.
Although the potassium-argon method has been used to date rocks on Earth for many decades, these types of measurements require sophisticated lab equipment that could not easily be transported and used on another planet.Without a way to reliably identify secondary craters, only subjective inferences can be made about the history of a surface.One might suppose secondaries could be identified by proximity to a large crater, or by similar amounts of erosion or space weathering. Some debris could go into orbit only to fall back centuries later, while other pieces could escape into space to eventually impact other bodies.In March, Curiosity drilled holes into the mudstone and collected powdered rock samples from two locations about three meters apart.Once the rock samples were drilled, Curiosity's robotic arm delivered the rock powder to the Sample Analysis on Mars (SAM) instrument, where it was used for a variety of chemical analyses, including the geochronology—or rock dating—techniques.