The Face of the Moon: How Old Is It?

The moon has a face like the clock in the hall – Robert Louis Stevenson

screen shot from the film where the rocket lands in the eye on the face of the moon
Le Voyage dans la lune

It’s the way we are wired up as humans that we ‘see’ faces in the most most extraordinary objects. “Face pareidolia – the phenomenon of seeing faces in everyday objects – uses the same brain processes that we use to recognise and interpret other ‘real’ human faces.” – UNSW Sydney

One of the most long lasting of these images is that of the face in the moon. As a species we have been staring up at that since we dropped down from the trees – perhaps even earlier.

Speaking at the Goldschmidt Geochemistry Conference in Lyon, a group of scientists, explained their work on aging that moon face.

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 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.

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; Earth has received a similar barrage throughout time, but the movements on the surface of the Earth will have masked these impacts.

 Professor Stephanie Werner (of the Centre for Planetary Habitability, University of Oslo) explained :

“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”.

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.

“We decided that we had to reconcile these differences, and that meant correlating individually dated Apollo samples to the number of craters in the sample site surrounding area – in effect, resetting the crater clock. We 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 we counted craters. This was a lot of work; we began this project in 2014. We found that by doing this we could resolve the discrepancy and push back the age of the surface of the Moon by up to 200 million years”.

Mare Imbrium from Apollo 17 crater on the surface of the moon
Illustration: Mare Imbrium taken from Apollo 17 in 1972. Left of centre is the Pytheas crater. Near the top is the Copernicus crater. Image credit: Credit NSSDC.

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. 

The researchers stress 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.

Professor Werner added:

“This is an important difference. It allows is 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. As this happened on the Moon, the Earth was almost certain to have also suffered this earlier bombardment too”.

The Goldschmidt Conference is the world’s main geochemistry conference. It is a joint congress of the European Association of Geochemistry and the Geochemical Society (US). It takes place in Lyon, France, from 9-14 July. Almost 5000 delegates are expected to attend.

(1) Sample-Based Spectral Mapping Around Landing Sites on the Moon – Lunar Time Scale Part 1 (2) ) Review and Revision of the Lunar Cratering Chronology – Lunar Time Scale Part 2. is published in The Planetary Science Journal

The moon has a face like the clock in the hall;
She shines on thieves on the garden wall,
On streets and fields and harbour quays,
And birdies asleep in the forks of the trees.

The squalling cat and the squeaking mouse,
The howling dog by the door of the house,
The bat that lies in bed at noon,
All love to be out by the light of the moon.

But all of the things that belong to the day
Cuddle to sleep to be out of her way;
And flowers and children close their eyes
Till up in the morning the sun shall arise.

The Moon by Robert Louis Stevenson

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