Geological clock reveals moon's age

The secret about when the midnight romance under a full-blown moon night on earth began is out.

A heartening discovery by an international team of planetary scientists has revealed that the moon formed nearly 100 million years after the start of the solar system.

"We were excited to find a 'geological clock' for the formation time of the moon that did not rely on radiometric dating methods. This correlation just jumped out of the simulations and held in each set of old simulations we looked at," said an excited Seth Jacobson from the Observatory de la Cote d'Azur in Nice, France.

The moon's age is defined on measurements from the interior of the earth combined with computer simulations of the proto-planetary disk from which the earth and other terrestrial planets formed.

The team of researchers from France, Germany and the US simulated the growth of the terrestrial planets (mercury, venus, earth and mars) from a disk of thousands of planetary building blocks orbiting the sun.

By analyzing the growth history of the earth-like planets from 259 simulations, the scientists discovered a relationship between the time the earth was impacted by a Mars-sized object to create the Moon and the amount of material added to the earth after that impact.

This is the first 'geologic clock' in early solar system history that does not rely on measurements and interpretations of the radioactive decay of atomic nuclei to determine age.

"This result is exciting because in the same simulations that can successfully form Mars in only two to five million years, we can also form the Moon at 100 million years. These vastly different timescales have been very hard to capture in simulations," explained Kevin Walsh from the Southwest Research Institute (SwRI) Space Science and Engineering Division.

Other scientists previously demonstrated that the abundance in the earth's mantle of highly siderophile elements, which are atomic elements that prefer to be chemically associated with iron, is directly proportional to the mass accreted by the Earth after the Moon-forming impact.

This estimate for the moon-formation agrees with some interpretations of radioactive dating measurements, but not others, said a paper published in the journal Nature.

Because the new dating method is an independent and direct measurement of the age of the moon, it helps guide which radioactive dating measurements are the most useful for this long-standing problem, the paper added.