Since the 1990's scientists have been able to date surface rocks by using the cosmic rays emitted by stars. Cosmic rays from ancient exploding supernovas bombard the surface of the Earth constantly. When those rays strike a rock on the surface they shatter the elements within the rock minerals. Magnesium, for example, decays into a particular form of helium. By determining the ration of helium to magnesium the approximate age that rock has been exposed on the surface can be calculated.
This method can be used to date surface rocks 10 to 30,000,000 years old and can tell when a rock fall occurred, a glacier melted or a volcano erupted.
Radiometric dating is similar but is used to determine when a rock formed based on the decay or half-life of heavier radioactive elements into lighter elements, such as uranium into lead. Radiometric dating is used for revealing the age of rocks as old as our solar system.
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| Strawberry Crater - 55,000 years old. |
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| SP Crater - 60,000 years old. |
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