As the Apollo missions matured, the astronauts could carry back larger volumes of samples. The Apollo 11 astronauts returned some 48 pounds (22 kg) of rocks; Apollo 12, 76 pounds (34 kg); Apollo 14, 94 pounds (43 kg); Apollo 15, 169 pounds (77 kg); Apollo 16, 210 pounds (95 kg); and Apollo 17, 243 pounds (110 kg). The Moon rocks were carefully wrapped and set into containers to prevent contamination, then sent away to a storage facility at the Johnson Space Center in Houston, where they reside today. Well, mostly: Some Apollo samples are periodically loaned out to museums or for research, and sadly, some lunar samples have been stolen, or turned up missing.
Along the trail of discovery, some Moon rocks have better stories than others. Genesis Rock, collected near Spur Crater by Jim Irwin and Dave Scott during Apollo 15, was originally considered extremely old because of its strange, whitish, fractured appearance. The thick rock, measuring about 3.5 inches (9 cm) across, was later determined to be 4.1 billion years old, not as old the astronauts had hoped. But the talk and analysis of Genesis Rock has made it the most famous of all lunar specimens.
Another famous rock was collected during the last mission, Apollo 17, and designated sample 70017. It is a titanium-rich basalt from the Taurus-Littrow Valley, and after an initial analysis President Richard Nixon ordered the sample sliced up and distributed to the 50 States plus 135 foreign heads of state.
After all of this effort and journey, what did the Moon rocks tell us? Ultimately, they revealed Apollo’s biggest story, the origin of the Moon itself. The most striking analytical finding showed the samples are eerily similar to Earth rocks in several ways. The signature detail was that oxygen isotopes sealed in Moon rocks — the “flavors” of oxygen atoms — matched those on Earth. This and other factors led to scientists in the 1970s proposing what came to be called the Giant Impact Hypothesis. Planetary scientists believe the Moon likely formed when a Mars-sized body, which they have named Theia, struck a newborn Earth some 4.5 billion years ago. The collision produced a ring of debris surrounding the young planet, which eventually accreted into the Moon. Much of the mass of Theia was absorbed into early Earth. This idea explains the tremendous similarities between Earth and Moon rocks.
The collection of Apollo Moon rocks returned to Earth, mostly residing in Houston, has given planetary scientists their first detailed look at the geology of another world. As a result, they have a pretty good idea of how the Moon came to be. Thankfully, we can study lunar science in the peaceful current age, only imaging what a violent and dangerous place the early solar system was.
For much more on the Apollo missions, make sure to check our special Celebrating 50 years of Apollo webpage, where you'll find everything you want to know about the equipment, plans, and people that made the Apollo missions possible.