Mankind’s Explanation:

 New Version


  “Taking all the evidence together, what conclusions can be made about the history of moon?  At some time more than 4.6 billion years ago, the moon began to be built up from a swarm of smaller bodies.  Either these bodies had already been degassed in some great heating episode, or the early moon contained volatiles that subsequently vanished from its crust.  Neither of these theories seems attractive.  If the volatiles were absent at the start, an implication would be that the moon formed much closer to the sun than it is now, and somehow was transferred out to a cooler part of the solar system where it became captured by the earth.  No plausible model for such a chain of events has yet been put forward.  A related theory has the moon building up within a giant incandescent silicate atmosphere of the proto-earth.  This model, too, encounters difficulties in meeting all the present data constraints.

   If the early volatiles were not absent, then they were present but have since been very thoroughly removed from at least the outer equatorial parts of the moon.  This raises the prospect of a baked-Alaska moon (cool inside, hot outside) at the outset, a possibility that would have required a very special series of events.  In any case, sometime after its initial formation the early lunar crust was thoroughly heated (perhaps by short-lived radioactive elements), chemically differentiated, and degassed.

   A giant bombardment by asteroid-sized objects went on, probably for millions of years, forming the repeatedly smashed and pulverized highland rocks called breccias, some of which include the oldest samples--4.6 billion years old--yet recovered from the moon.  The crust then cooled enough to become rigid, preserving much of the topography of the huge impact basins and their surrounding ejected matter.

   A billion or more years later, the lava flooding of the basins that are now on the moon’s earthward side began, creating the maria and the mascons.  Long-lived radioactive elements may have provided the energy for this second and long-continued episode of partial melting.  Meanwhile, a diminishing number of meteorites continued to fall on maria and highlands alike, pulverizing the surface and creating the broken-up surface material called the regolith.

   One discovery made by the Apollo astronauts while walking on the moon is that the regolith is rich in blobs and spherules of glass, formed by the rapid cooling of materials melted by impact shock.  An important finding of the Apollo seismic experiments is that the regolith causes great dispersion of seismic waves because of its chaotic structure.  Also, the regolith has very low damping, when struck, the moon “rings” much longer than the earth.  Only at great depths do the waves propagate as if through solid rock.

   After the formation of the maria, it seems that the moon has just been cooling and quieting down.  Three billion years ago it may have looked much as it does today.  The only more recent changes are those wrought by occasional volcanic emanations and the continuing influx of meteorites, dust, elementary particles, and radiations.

   This simplified picture ignores the variety of local tectonic and morphologic features on the moon.  It leaves unsolved the problem of origin, and it is silent on such subjects as the possibility of polar cold-trapped volatiles.  Truly, there is much more to be discovered by future explorers of the moon.”

See also SPACE EXPLORATION.  James D.Burke, Jet Propulsion Laboratory California Institute of Technology




Alfven, Hannes, and Gustaf Arrhenius, Evolution of the Solar System (USPGO 1976).

Baldwin, Ralph B., A Fundamental Survey of the Moon (McGraw-Hill 1965).

Cherrington, Ernest H., Exploring the Moon through Binoculars and Small Telescopes (Dover 1983).

Gully, Rosemary, Moonscapes: A Celebration of Lunar Astronomy, Magic, Legend, and Lore (Prentice-Hall 1991).

Kopal, Zdenek, The Moon in the Post-Apollo Era (Reidel 1974).

Runcorn, S. K., et al., eds., The Moon: A New Appraisal from Space Missions and Laboratory Analyses (Royal Society 1976).

Taylor, Stuart R., Planetary Science: A Lunar Perspective (Lunar and Planetary Inst. 1982)



Information acquired within the quotes is from: Encyclopedia Americana-International Edition

Copyright 1994, Grolier Incorporated, Volume 19, page 437

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