In 1961, President John F. Kennedy stood before the U.S. Congress and declared a goal of placing a man on the moon before the current decade had ended. With this action, he placed the country on a course of exploring the Moon through a series of Apollo missions. These culminated when the crew of Apollo 11 fulfilled Kennedy’s promise and when subsequent missions repeated the feat.

While the Apollo missions and other research helped extend our knowledge of Earth’s nearest neighbor, what did we know before then? How much of this knowledge changed? Let’s take a look.

Theories about the moon’s surface

Prior to the Apollo missions, popular lore indicated the moon was made of green cheese, that it was hollow, and that it was possibly inhabited. In the scientific community, many suspected the moon’s surface was almost fluffy and worried that it was so soft any vehicle landing on it would sink.

As it turned out, these theories were disproved. The moon doesn’t yet appear to support life and has a firm crust. In fact, once scientists began collecting samples from the moon’s surface they confirmed it was made of oxygen, silicon, magnesium, iron, calcium, and aluminum with extremely small amounts of titanium, uranium, and other trace elements.

The Apollo missions also confirmed that the moon wasn’t hollow. To get a better sense of the moon’s firmness, crews from Apollo 11 crashed their lunar lander into the moon’s surface with an impact equal to the force of a ton of explosives. It shook the moon for about an hour. Similarly, Apollo 13 and other mission crews crash-landed even more equipment producing even stronger vibrations.

Knowledge of lunar layers

Scientific understanding of the composition of the moon evolved beyond simply establishing that it was solid. As researchers examined the nearly 50lbs of samples that NASA crews brought back from the moon, they learned even more about what the moon was made of. They ultimately identified that the moon contains a crust, a mantle, and a core similarly to Earth and gained some understanding of what each of these sections may be made of.

The moon’s age and how it was formed

Apollo mission samples are also helping to more accurately identify the moon’s age, suggesting it is 4.5 billion years old. This dates the moon’s origin to a time that is close to the earliest days of the solar system and ages appear to vary based on the specific location where a moon rock sample was found.

Through the years, there have been many theories to describe how the moon was formed. In the 19th Century, Charles Darwin’s son believed the moon was formed in the very early days of the solar system when a fast spinning earth ejected molten material into space. Others have believed that the moon was formed at the same time as the Earth, developing as its satellite. A third theory is that the moon is the result of collisions between planetary debris.

The challenge for understanding the moon’s origin remains and the most current working theory has some elements of things that were previously proposed. It proposed that while the Earth was still Magma-covered, a giant planet-sized body slammed into it. Scientists support this theory because it verified observations scientists have documented through the years.

Formation of the moon’s craters

For as long as scientists had been able to use telescopes, they could observe craters covering the surface of the moon. Researchers guessed that the craters were formed by either volcanic activity or by a series of impacts with smaller objects from space. With the Apollo missions, scientists were able to more closely observe the moon’s surface and to retrieve samples for analysis. Ultimately, this work points towards the idea that craters were caused by collisions. Because the moon doesn’t have rivers, these impacts remain undisturbed.