The Cosmic Dust Laboratory at JSC. Cosmic-dust particles are typically about a micron in diameter. For comparison, a normal human hair is about 30 micrometers in diameter. Contamination, then, is a big no-no. That's why everybody who enters the Cosmic-Dust Lab has to dress like a Q-tip. When other geoscientists are talking about them, for better or worse, geochemists and petrologists are often put into one group. These are folks who study, among other things, the chemistry, mineralogy, and textures of rocks to learn more about the conditions of formation of the rocks and their constituent minerals. In doing so, they can get a better idea of what the environment was like in that part of the planet where the rocks originated. When rocks are studied on this kind of level, though, things get very complicated very quickly. Not only are there all those elements to worry about, but they occur in different configurations in the different minerals that make up the rock. (Check your periodic table -- most of those elements are found in rocks. Then there are the different isotopes, which can make matters even more complex. On the other hand, the different isotopes can be extremely useful, too. More about that later, maybe.) The worst part of all this is that many of those elements occur in only trace amounts -- well under a part per million in many cases. A part per million is roughly a paper clip's weight relative to a small car, like a Honda Civic or a Ford Aspire. Not much. Geochemists who work with lunar samples and cosmic-dust particles have developed techniques that will allow them to analyze particles of rock as small as a few micrograms -- or a few millionths of that paper clip. Geophysicists and other planetary scientists who look at big things like volcanoes or craters or asteroids are continually amazed at the amount of information that geochemists can derive from something that makes a grain of sand look as big as a house. Not only are thin sections extremely useful from a scientific point of view, but they can be really nice to look at, too. This is a thin section of Apollo 12 basalt 12004, which is more than 3.2 billion years old. Petrographers -- scientists who, among other things, classify rocks on the basis of their mineralogies and textures -- use them to evaluate the different relationships between the component minerals. The colors result from the use of polarizing filters in the light path. Each mineral puts its own "signature" on the beam of light passing through the thin section, and the polarizer is used to decipher that signature. Among other types of analysis, petrologists look at thin sections of rocks (slices of rock that are just about as thick as a hair on your head, which means that light passes right through them) with special "petrographic" microscopes. These microscopes have more controls and gizmos hanging from them than you might want to imagine, but they're all there for a reason: to polarize or otherwise manipulate the light passing through the thin section. It's great when the geochemists can tell us how much of a specific trace element is in a speck of mineral that came from that rock over there, but that information must be placed in the correct context. For instance, did that rock have an igneous origin -- that is, did it solidify directly from a liquid, like lava? Or is it a sedimentary kind of rock, which was once fragmental material like lunar soil and maybe hardened into a breccia by a strong shock wave? Petrologists can tell an awful lot about a rock's history just by looking at a thin section for a while. When you hear something like "scientists will be analyzing the lunar rocks for years to come," well, that's why. There are a lot of samples, and they hold a lot of information for us to uncover. Unfortunately, they came from just a few locations on the Moon. How would you like to be asked to come up with the history of the entire Earth from a couple samples from, say, the Sahara Desert, Siberia, and the middle of the Pacific Ocean? This is very similar to what lunar scientists have been trying to do since 1969. And another thing -- in the 1960's, when NASA was preparing to get the lunar samples and analyze them, it invested quite a bit of money into developing techniques to measure very small traces of elements in very small quantities of planetary materials. The result is the kind of capability described above. Not only that, but many of the analytical techniques used in crime labs, medical institutions, and other scientific and engineering facilities are direct spin-offs of those used on the lunar samples and meteorites.