The '69 moon landing was science-free. Until someone said, "they'd better have something to do." So they studied rocks.
In three, short years — five decades ago — human space exploration set us on a path we're still traveling today. The American space agency landed six times on the moon.
One mission — Apollo 13 — was aborted, with that famous line, "Houston we've had a problem." An understatement after an oxygen tank blew up.
But all-in-all it was a monumental time for Western politics, science and technology.
Rockets got built, flags got waved and astronauts brought 382 kilograms of lunar rocks and other soil samples back to Earth.
Read more: From Apollo 11 to the new space race
The astronauts will need something to do
It's hard to imagine that science almost got overlooked.
"The scientists wanted to learn more about the moon, but they were kind of secondary in the early days," says Professor Simon Kelley, who heads the School of GeoSciences at the University of Edinburgh.
Read more: Asteroids and comets: How to tell them apart
"The first step was the technology — beat the Russians, develop rockets and missiles," he says.
But the scientists, including one Eugene M. Shoemaker, were getting restless.
So enter Max Faget, a director of engineering at NASA's Manned Spacecraft Center.
Faget has been immortalized with the line: "It wouldn't look very good if we went to the moon and didn't have something to do when we got there." Too true.
Read more: A cinematic flight to the moon
Apollo 11 astronauts training in geology. Neil Armstrong uses a sample scoop. Buzz Aldrin films him on a Hasselblad camera
"So, it evolves through the program," Kelley continues. "But it wasn't until Apollo 17 — the final mission — that someone with a geology background actually went to the moon."
That was Harrison Hagan "Jack" Schmitt.
Before Schmitt, the astronauts tended to be aeronautical engineers, military men, test pilots. The sort of men — and it was all men, and true to the cliché, white men — who knew the risks of human space flight and didn't mind taking them. Tough guys.
Only one other Apollo astronaut had a science background — Richard F. Gordon Jr.
Gordon was the Command Module Pilot on Apollo 12. And a chemist. But he never set foot on the moon, so does he even count?
Tough guys got good at geology. By Apollo 15 in 1971, they found a sample of the moon's primordial crust.
Looks like lunar geology
Those who did walk on the moon had to train in geology. And they did that in places like Texas, Hawaii, or Iceland, places of remote geological and volcanic interest.
They also learned how to document their trip and finds with Hasselblad cameras.
The idea was to teach them how to "see like a geologist," understand what the colors of different rocks mean, or how to interpret rock textures.
"And the moon is really, really simple," says Kelley. "There are two main types of rock on the moon."
"First, there's basalt that flows from volcanoes just like on Earth," he says.
"And the other," says Kelley, "is the smashed remnants of that same material, which has been hit by thousands of meteorites and ends up in the sediment, stuck together with glass and other things." That's called Breccia.
Loads of samples
The Lunar and Planetary Institute in Houston, Texas, lists 941 samples of Lunar rock and dust, including basalt, breccia (debris from impact craters), plutonic rocks (coarse, crystalline rocks that cooled slowly), and soil.
Scientists can learn a lot about the history of the moon, or any planet, from a single grain of sand. A rounded grain, for instance, shows that it's been moved by water.
"You won't find a lot of rounded grains on the moon because we don't have any history of water there, except the recent history from orbiters that show there may be ice at the polar craters," says Robert Anderson, a geoscientist and research supervisor at NASA's Jet Propulsion Laboratory.
"So, a lot of the particles on the moon are very angular, very sharp," Anderson says. "You can tell they were formed when meteorites hit the moon, and that forms glass. The moon has a lot of these glass beads."
Read more: Our first InSight into the interior of Mars
The astronauts practiced to scale. Armstrong sending a rockbox up to the lander. Does this explain the conspiracy theories?
They don't only look pretty. They also tell scientists that if we ever want to build a moon base, astronauts will probably have to take water from Earth — for drilling or to make a kind of lunar concrete.
"We understand how hard the rocks are, so if we want to get materials from them, we know how to do that," says Kelley. "There's all this physical data that they brought back during the Apollo landings."
All smiles at NASA: The first Apollo 11 sample return container, containing lunar surface material, arrives at Ellington Air Force Base
From the moon to Mars
Moon geology during the Apollo era meant hard labor.
"On the moon, the astronauts went down about a meter and they did it by physical quarrying as you would on Earth. It was very difficult, with a spacesuit on and one-sixth gravity and all the laws of Newton acting on it," says Anderson.
Things are a little different on Mars. Anderson helped develop a drill for NASA's Mars Science Laboratory (MSL), a spacecraft which landed a rover called Curiosity on the Red Planet in 2012.
It has delivered useful data, including the apparent presence of clay, which tends to form in water. But it had its geological challenges too.
"One of the problems we had on the MSL drill was that a lot of the drilling on Earth is done with fluids to remove heat and to remove the cutting," Anderson says. "But you can't do that on planetary surfaces, because if you added water it would bubble off like a rocket exhaust."
But Mars does have water.
"It's not like water on Earth. But below the surface in the pores between the grains there is frozen water and perhaps CO2," says Kelley. "So Martian rocks might be easier to fuse [than moon rocks], because water makes rocks fuse at lower temperatures."
More insight into Mars than the moon?
Six years after Curiosity, an international team launched the InSight mission to Mars.
InSight aims to drill about three meters into the planet to detect heat flows — another sign of planetary life — and tectonic activity.
It's another "work in progress" that occasionally leads people to complain that scientists should rather focus on the moon — it's closer and we've been there before.
Plus, Mars missions lack that human touch — they are robotic, so we've never got anything back.
But think of Mars as being on a continuum from the Earth to the moon and beyond —starting with the American and Soviet missions of the 1950s and 60s — and it starts to make a little more sense.
"Humankind has sent several sophisticated missions to Mars," says Kelley. "But people still talk about putting astronauts on the planet, even though it takes such a long time to get there, and it's so dangerous, because they learnt so much by having astronauts on the moon."
One day, people may want to live on both. Perhaps.
"Once we understand the technology of getting there," says Anderson.
And the technology to get back?