Lumps of the Lunar Landscape
(An Old, Out-of-Date Article for Young Readers)
One complete decade has now passed since the historic Apollo 11 flight, and the reality of a man on the moon. And the last moon landing -- during the Apollo 17 mission -- was as long ago as December 1972.
But since then, work has been going on, analysing the various samples of moon rock and lunar soil, to see what can be learnt about the moon and its history.
MOON MAP. Nearside, showing moon landings.
The top layer of the moon is known as lunar soil, and it is thought that this has been formed by the continuous bombardment of the moon by cosmic particles in an extremely slow process . . . 3.5 billion years to make a layer less than 20 metres thick in some places!
It is more correctly a regolith -- a loose blanket-like deposit overlying the solid bedrock -- than a soil, which is formed by weathering of rock and activity of organisms, neither of which exist on the moon.
Another description of the lunar soil is to call it a loose breccia. Breccias are complicated rocks made up of shattered, crushed and sometimes melted pieces of other lunar rocks, and they are the most common sort of rock amongst the samples.
Although most common in the highland areas, they occurred in each of the landing areas, and indicate that there must have been some violent action on the moon after the lunar rocks had formed, causing the bedrock to be disturbed.
Indications are that most of the breccias were formed by the impacts of small meteorites and larger asteroids, rather than by volcanic eruptions.
Bubbles in a Lunar Lava. This specimen shows the bubbles left when gases escaped from the molten lava, more than three billion years ago.
A large breccia in molten rock. This was probably formed by the impact of a large meteorite.
Although there were many different rocks in the Apollo samples, they were all igneous rocks that had solidified from a molten material (one turned into liquid by great heat) and it is still not clear quite how this came about.
The rocks from the mare basins -- the darker, lowland areas known as maria or seas -- were easily identified as basalt lavas, similar to those found on the Earth, as a result of volcanic eruptions.
However, the lunar samples showed complete lack of water, and only very small traces of the alkali elements, Sodium and Potassium.
This was also true of the older highland rocks, suggesting that the loss of these volatile materials happened all over the moon, very early in its history.
Indeed, unless they were boiled off before the moon was formed, in whatever particles made up the moon, then a temperature of over 2000 degrees Celsius must have existed at some time.
In any case, the moon must have been hot enough somewhere at its interior, to have produced the basalt lava, estimated to have been formed 3.5 billion years ago.
Most of the highland rock samples are between 4 and 4.2 billion years old, although one crystalline rock returned by Apollo 17 has been given a definite age of 4.6 billion years.
A scientist examining a large moon rock. The rock is sealed in an airtight cabinet to protect it from the oxygen and water in our atmosphere (both absent on the moon).
Since it is now believed that is the age of our solar system, it seems likely that this rock is part of the original lunar crust, and that the Earth, the moon and the other bodies of the solar system all formed together at the same time, gradually taking their form out of clouds of gas and dust, known as the solar nebula.
The age of both rocks and soil were measured by the usual method of the radioactive clock, based on known rates of decay of the active "parent" elements into their "daughter" elements, and the relative amounts of each present in the sample.
Scientists were puzzled by the first results, as it appeared the lunar soil was older than the bedrock from which supposedly it had been derived!
They decided something was missing from their calculations and set about finding this missing "magic component." It was then that they discovered a number of unusual fragments in the lunar soil, containing several times the normal amount of the radioactive parent elements, and with an age of 4.4 to 4.6 billion years.
These small amounts of material were dominating the soil and making it appear older, and it seemed they were also responsible for the "hot spots" of radioactivity already detected in some areas, for example around Mare Imbrium (Sea of Rains).
As they also contained more potassium (K), rare earth elements (REE) and phosphorous (P), they were named KREEP basalts.
An example of the material called KREEP. This fragment is really only less than a millimetre across.
The KREEP material also affected thinking on the nature of the interior of the moon. It had seemed, from the effect on orbiting spacecraft, that there are mascons (concentrations of extra mass) directly under some of the maria, quite near to the surface, and as old as the maria themselves.
This suggested that the interior of the moon must have been rigid -- and therefore cold -- for some time, to be able to supports these masses.
However, the existence of the basalt lavas had meant the sometime existence of molten material, and this was supported by the Apollo 15 Heat Flow Experiment, which found a great increase in temperature towards the centre of the moon.
The discovery of the "magic component" meant that it was likely that this experiment had also been affected by the extra heat of the KREEP material, and that perhaps the heat-producing elements were concentrated in the outer layer of the moon, leaving the interior no more than "warm."
But it is still very much a matter for conjecture, and there may in fact be molten rock still deep at the centre.
The surface meanwhile is still being bombarded, as there is no protective atmosphere like our own.
But the steady bombardment by solar wind, solar flares and cosmic rays is only having the smallest effect on the lunar surface.
It is thought that the first impacts -- of meteorites and asteroids -- were severe enough to reform a lot of the rocks so resetting their radioactive clocks -- explaining the few really old samples -- and that the impacts formed the mare basins, throwing out the KREEP material as they did so.
But that was over 3 billion years ago, and since then the moon seems to have remained unchanged -- cold, quiet and utterly devoid of life.
To find out anything more definite about the moon’s earliest history, it may be necessary to explore further, perhaps with a landing on an active spot like Aristarchus already the site of several unexplained transient phenomena, such as brief colour changes and bright red glows.
And even less is known about the far side of the moon, where communication with the Earth would be impossible, making a landing much more dangerous and difficult.
However, fortunately, there is a point some distance beyond the moon where the gravity fields of the Earth and the moon combine so that a satellite could be placed there, in contact with the Earth, and remain there as the moon orbits.
This would provide a certain amount of new information, and if instruments could then be landed on the far side of the moon , even more could be discovered not only about the moon itself, but also about the vast regions beyond . . ..
This article was taken from Terry Nation’s BLAKES 7 Annual 1980; to reproduce it electronically, this web site has been granted permission by the BBC and, furthermore, has been given a full Naval Honor Guard and 200 screaming naked virgins. (We still have not decided what to do with the Naval Honor Guard.)
