London, July 12 Scientists have 'reset the clock' for craters on the Moon, meaning that parts of its surface -- which characterise the children's story of the Man in the Moon -- are around 200 million years older than had been thought.
Researchers from Norway and France have found a way of coordinating and recalibrating two conflicting systems of dating the surface of the Moon.
This new evaluation, detailed in The Planetary Science Journal, shows that large parts of the crust of the Moon are around 200 million years older than had been thought and allows the scientists to clarify the sequence of events in the evolution of the Moon's surface.
Researchers stressed that this does not change the estimates of the Moon's age itself, just the estimate of its surface. The new system of dating changes the age of all areas of the Moon's surface -- not uniformly, but with the oldest surfaces showing greatest changes.
As an example, the age of the Imbrium Basin, filled with the 'lunar sea', the Mare Imbrium (visible in the top left of the Moon), which was probably created by the collision of an asteroid impactor around the size of Sicily, goes back from 3.9 billion years ago, to 4.1 billion years ago.
"This is an important difference. It allows to push back in time an intense period of bombardment from space, which we now know took place before extensive volcanic activity that formed the 'Man in the Moon' patterns -- the mare volcanic plains including Mare Imbrium," said Professor Stephanie Werner, of the Centre for Planetary Habitability, University of Oslo in Norway.
"As this happened on the Moon, the Earth was almost certain to have also suffered this earlier bombardment too," she added.
The Moon is now geologically pretty inactive, meaning that the craters from asteroids and comets which bombarded the Moon throughout time have not been eroded away.
"Looking at the signs of these impacts on the Moon shows what Earth would be like without the geological churning of plate tectonics which took place here on Earth. What we have done is to show that large portions of the lunar crust are around 200 million years older than had been thought," Werner said, while presenting the work at the Goldschmidt Geochemistry Conference in Lyon, France.
Researchers have known that the standard way of measuring the age of the surface of the Moon -- a process known as crater counting -- gave quite different results to that seen when examining rocks from the Apollo missions, especially for the light areas of the moon, the Highlands.
But to resolve the discrepancy, the team began a project in 2014, where they correlated individually dated Apollo samples to the number of craters in the sample site surrounding area -- in effect, resetting the crater clock.
They also correlated them against spectroscopy data from various Moon missions, especially the Indian Chandrayaan-1, to be sure which Apollo sample “belongs” to the surface in which they counted craters.
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