The Scientific Legacy of Apollo (notes based on the Scientific American article 7/1994)
Seacrest School Moon Crew, Naples, Florida (team discussion 2011)
Notes from the Sci. Am. Article. Read the notes, and examine the photographs in the article.
The 12 Apollo astronauts who travelled to the moon 1969-1972 were time travelers. Their journey of
250,000 miles to the moon also took them billions of years into the past. The moon lacks any of the
erosion and weathering found on Earth, so its entire history is visible on its surface. The moon is almost
unchanged from 1, 2 or 3 billion years ago; NOTHING happens there*. So the astronauts were easily
able to collect rocks, dirt, and dust showing the deep history of the moon back to its origins over 4
billion years ago. All the rocks from the moon that NASA brought back to Earth (over 600 pounds) show
a violent and surprising history; the instruments placed on the moon’s surface by the Apollo astronauts
have revealed the interior structure of our satellite. Without the moon landings we would know almost
nothing of the deep history of the earth and the moon.
Why is so much earth history missing from Earth? Erosion, rain, snow, earthquakes, volcanoes, plate
tectonic action, ice ages, etc. all have conspired to destroy any original earth surfaces. The earth has
some feaures that were formed today, yesterday; some 100 years ago; many that are 1000s of years old;
but very few that are billions of years old. For us this is probably a good thing since erosion and other
Earth processes make our planet more habitable for us. But if you want to understand the deep history
of the planet, it is hard to find evidence of the past. The Moon is the opposite twin of Earth. Almost
everything on the Moon’s surface is very, very old and hardly anything is new.
What good are moon rocks? The 382 kg of rocks brought back from the moon allowed us to accurately
date the moon’s surface and for the first time ever to understand the age of the moon itself. It has an
age! The moon formed at the same time as did the earth, 4.5 billion years ago. Measuring quantities of
radioactive materials in the rocks confirmed that the ages of the moon and Earth are similar.
Where did the moon come from? There were several theories or models of its formation:
1. Was it captured from somewhere else in the solar system? A fully formed moon comes along in
space and enters a precise orbit so as to become gravitationally linked to the Earth forever. This
was always thought to be highly unlikely, given the incredible alignments, orbits, and velocities
required for an object to be captured by the earth and not collide with it or get slung out further
into space. The Apollo rocks show us that the Earth and the Moon are made of the same stuff
and formed in the same place. If the moon formed anywhere else in the solar system it would
be made of entirely different materials. The Capture Model is not supported by the evidence.
2. Did the moon get flung out of the early earth? Charles Darwin though of this first, suggesting
that the moon was a blob of material ejected from the Earth. The light weight nature of the
moon suggests this could be true; but how could it get slung out of the earth? There is no
manner this could happen unless the Earth was spinning at an enormous speed. There is no way
the Earth could spin that fast and then slow down to today’s rate of once a day. The physics of
rotating says that this scenario is impossible. But the moon and Earth do resemble each other…..
3. The Apollo rocks refine this story with real evidence. The Earth and Moon are very similar but
different chemically in revealing ways. Chemistry really does matter here…..
Earth
Moon
Water, everywhere
no water, NONE**
Volatile elements
no volatiles (sodium, potassium) (volatiles are things easily
boiled away)
All elements
Abundance of elements that boil at high temps. (aluminum,
calcium, thorium called “refractories”)
This suggests that the moon was “cooked” to boil away all the water and volatiles but not
cooked enough to remove the refractories: the
heavier elements.
Key ideas:
Volatiles are substances that vaporize easily and will “boil” away: potassium, sodium, bismuth,
thallium, water, common gases. The presence
of these materials means something has
remained cool; the absence implies that the
moon was extremely hot at one time
Refractories: substances that boil at very high temperatures. These materials ( aluminum,
calcium, thorium,
and other rare-earth
elements) are much more common on moon’s
surface that on earth. 42-3
4. The Double Planet Hypothesis: Maybe the moon was formed along with the earth at the same
time, a double planet. That’s a great idea! But it can’t account for the chemistry in #3 above or
the spin and rotation of the two planets. It also fails to account for the iron core of the Earth
being huge and the moon being tiny. So this is a great theory, but the evidence does not
support it. 42
5. Bad idea? Or maybe………Here is an idea that was suggested 66 years ago, that no one liked: just
after it formed and was still a really HOT blob, Earth was hit by a large object, about the size of
Mars. The large object joined with the earth and threw out a huge splatter of matter into orbit
around the earth: viola! The Moon. What a contrived impossible event!
But wait: it accounts for all the known evidence.
a. The moon consists of the surface materials of the Earth
b. The Earth has most iron, the moon least (the iron of the impactor added to and collected in
the core of the new Earth) but didn’t get blasted into space around the Earth.
c. The collision involved high temperatures that eliminated water from the new moon as well
as any elements that vaporized easily (the volatiles); the heavier elements with high boiling
points knocked into orbit remained there in the new moon.
d. The earth and the impactor formed in about the same place in the young solar system, so
they had the same amounts and kinds of oxygen. (O16 to O 18)
e. The rotation and spin of the Earth and moon match this scenario. This is why the Earth spins
at 24 hour period and the moon at 27+ day period.
f. Life in the Earth solar system was dangerous. It is likely there were planet sized objects
moving in irregular paths that could have collided with Earth. Other irregular objects hit
Mercury and Uranus giving them tilts or odd compositions. Eventually all irregular moving
objects left the solar system or hit something. What remains is a bunch of planets in boring
circular orbits that go on for billions of years, not bothering each other. 43
So now the Giant Impactor or Huge Collision Theory is the best model of how the moon came to be. The
chemical evidence from the lunar rocks from Apollo and the ages of the rocks support this idea. That’s a
good theory- one that accounts for all the evidence and doesn’t involve unusual circumstances.
What was the moon like after it formed.?
Magma ocean. Get a large glass. Pour in a soda of your choice, some Kosher salt, then ice cubes. Let
sit. Then using a pipet, add some pure ethy alcohol to the surface where it will stay floating since it is
less dense than water. Stop! You’re underage….. But the finished mixture doesn’t mix…..the water is
on the bottom, the ice cubes float in the water, and the alcohol floats on top of the ice cubes. Heaviest
stuff—the salt crystals, are at the bottom. Liquids will layer themselves (stratify) by the density of the
materials in them.
The baby moon is an ocean of liquid rock. The different substances sort out like the glass above. Heavy
elements join and sink; light elements float toward the surface. So the iron and magnesium compounds
sink toward the core of the moon; aluminum, calcium, titanium float to the surface. Then it cools. The
ancient surface of the moon should be lighter elements. It is! The ancient moon must have been an
ocean of super heated lava, heated from the collision of the Giant Impactor with Earth.
This is the MAGMA OCEAN model. In a liquid moon, lighter, less dense materials form a crust on the
surface of the moon. These rocks are also found on earth: Feldspars. Denser materials sink toward the
core of the moon: they are iron containing materials called: olivine and pyroxene. Notice how
chemistry (chemical compounds and density) provides evidence of the moons developmental history.
How did the moon get so hot to create the magma ocean? The Giant Impact – image 2 planets colliding!
And also as metallic iron sinks into the core of the moon it would release still more heat. (44)
The Apollo moon landings (now over 40 years ago) provided the only real on the ground evidence to
understand lunar and planetary formation. The model is still being developed by more modern
satellites (Clementine and LROC) 45
Then the moon gets shot full of holes. All the “holes” in the lunar surface were once thought to be
volcanic. Satellites and the Apollo missions confirmed that the craters are made by impacts; often
gigantic asteroids smashing the moon’s surface to bits, leaving craters 100s of miles wide. The oldest
moon surfaces (usually called the highlands) are smashed melted, mixed, crushed, and bashed. The
rocks found there by Apollo 16,17 are called brecchias (means broken?) which are melted mixtures of
lots of kinds of rock.
What are the smooth areas on the face of the moon? These are vast lava flows the filled in giant crater
impacts. From the Earth they look like oceans, so they were called “Mare” by the first lunar observers.
Mare Imbrium was a colossal impact that made a hole 800 miles wide, and deep enough to tap into the
deep magmas from the inner moon. The mares have all flooded with lava from the inner moon, bringing
some heavier elements to the lunar surface, somewhat confusing the surface with some older and some
newer rocks. Their compositions (and appearance) and ages are clearly different, so it is pssobile to sort
out the dates and sources of the moon’s rocks.
3.9 billion years ago, the very new moon which was being pelted with ordinary impacts, suddenly got hit
with a storm of meteors and asteroids that obliterated the entire surface. This bombardment was so
intense that it totally reworked the moon’s surface, making what we see today. Most of the rocks
collected by Apollo date from this era: 3.85 to 3.95 billion years ago. That’s the Lunar Cataclysm! Note
the word “suddenly” applies in a geologic sense. We are still referring to a 100 million year period of
intense crater formation: that’s a lot of time by our standard! But notable in the huge time span of
planetary development. Since then -- 3+ billion years, there has been very little crater activity.
Also note the location of the moon. Not too far from Earth. If the moon got blasted 3.85 billion years
ago, so did the earth. The Earth would have had 100s of huge impact craters, 100s of miles across. The
largest impacts would have made basins more than 1000 miles wide. This process would have brought
dense elements to the young Earth’s surface and may have led to the formation of the first continents.
Only after the results of this bombardment period ended and cooled off would there have been an
opportunity for life to get started. There is strong evidence that life on Earth first emerged about 3.6
billion years ago, 200 million years after the Bombardment period ended. That is what the young solar
system was all about: The duck and cover days of meteor bombardment. The Lunar Cataclysm theory of
lunar development has become more accepted in the 1990s and 2000’s. Some lunar rocks do date from
earlier than 3.85 billion years. These rocks are thought to be survivors of the bombardment, and
evidence of the moon’s real age 4.5 billion years.
(Lunar rocks are dated by measuring amounts of Uranium and Lead. The date of the rock is the last time
it melted. So the oldest moon rocks (4.3 billion years) haven’t melted since then. Newer moon rocks at
about 3.85 billion years, melted during the cataclysm. )
What does the moon tell us? It reveals the deep history of the Earth-Moon system, casting light on the
process of planetary formation in our solar system. Any return trips to the moon will be able to answer
more specific questions of the timing of the bombardment the we see today on the Moon’s surface but
has been weathered and eroded away on Earth.
*something does happen on the moon’s surface, but very slowly. With no atmosphere, the moon is
zapped by solar radiation which does change the surface layers of rock, soil, and dust.
**The moon rocks have no water molecules in them. Many substances on Earth have water molecules
attached in one way or another. Moon is super dry, BUT there may be water ice at the north and south
poles in permanent dark craters. Water has a funny way of showing up everywhere, it is a very common
substance throughout the universe.