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December 01, 2005
How old is the Moon?
Do you know? I've learnt a few day ago that is 4,527 million years old - give or take 10 million years that is. At least that is what a team of scientists from Münster and Köln in Germany and Oxford Great Britain say. But how do they know?
They analysed the content of the metal isotope Wolfram-182 in a number of rock samples taken during various Apollo missions. During the first 60 million years of our solar system Wolfram-182 was partly formed by the radioactive decay of Hafnium-182. But being a very instable isotop Hafnium-182 vanished completely within these first 60 million years. That means that if variations in Wolfram-182 content are found in rock samples the rocks must have been formed within the first 60 million years. If the rocks had been formed after the first 60 million years one would expect no variations in Wolfram-182 content of the rock samples because in that case Hafnium-182 would not have contributed to the Wolfram-182 content.
Variations in the Wolfram-182 content were indeed detected in the rock samples from the Moon. These enabled the scienstists to calculate that the Moon must have been formed 30 to 50 millions years after our solar system, i.e. 4,527 million years ago. The Moon itself is most probably the product of a collision between the so-called proto-Earth and a marslike object as described in the "Giant Impact Hypothesis". According to this hypothesis the Earth as we know it is as old as the Moon. The oldest rocks which are found on the Earth are at least 500 million years younger than the Earth itself and therefore useless for exactly determining the age of the Earth. But now the rock samples from the Moon, which contain information about both Earth and Moon, will certainly open up new insights into the hour of birth of our own planet.
Posted by Mausi at December 1, 2005 12:29 PM
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