David Scott, who became the first person to drive on another world in 1971, likened the undisturbed landscape to a picture by the photographer Ansel Adams. “There was no color, but great contrast between the brightly illuminated surface and the black shadow of the mountain slopes and craters where no sunlight fell,” he wrote in a 2004 memoir. And the smell! “The moon turned out to have a slightly metallic smell, almost like gunpowder, which pervaded the [lunar module] for the remainder of our trip,” Scott recalled.

These experiences and others are well documented—in grainy footage and scratchy audio, flight transcripts, books, documentaries, Hollywood films, and countless news reports and interviews. There’s a wonderful little clip of Jack Schmitt, one of the four remaining moonwalkers, pleading with Mission Control to let him throw his hammer into the lunar sky before getting into the lander to go home. Schmitt, 84 years old now, is the first and only scientist—a geologist—to have visited the moon, and it must have seemed appropriate to leave behind his profession’s tool of choice. “Look at that!” he exclaimed after the flight directors assented and the hammer tumbled, end over end, a small white smudge moving in an arc over the hulking gray background. Schmitt had spent a total of 22 hours outside the capsule, helping to produce the biggest haul of lunar samples.

Read: The best banter from Apollo 11

But these records are not as evocative as hearing from the moonwalkers themselves, says Charlie Bolden, a former space-shuttle astronaut who served as NASA administrator in the Obama administration. When the last moonwalker dies, “it will be like the day we lose the last veteran of World War II—and we’re perilously close to that day—or the last Korean War veteran,” Bolden says. “You will lose any semblance of opportunity to listen to people and hear their firsthand experience.”

Bolden had that chance in 1980, as a new NASA recruit from the Marine Corps. The Apollo astronauts would stop by the NASA astronaut office in Houston once a year for their annual physical exams and reminisce with the newbies. Alan Bean, the Apollo moonwalker who died last year at age 86, was a mentor to Bolden’s class during training.

“Here’s a guy who had walked on the moon, who gave up a year of his life when he could be doing all other kinds of things, to shepherd around these snotty-nosed kids who aspired to be astronauts,” Bolden says. “You know how you see the day-school caregivers walking around with the kids on a rope? That’s kind of the way it felt.”

The Apollo astronauts’ memories of the surface are easier to preserve than the distinct cognitive experience of looking back at the Earth. Some astronauts who travel into Earth’s orbit say they come home with a distinct shift of perspective on the planet. From up there, this ball of swirling blues and whites, suspended in the inky blackness of space, looks fragile, especially against the perilous backdrop of climate change. The effect would only be magnified on the moon, where Earth appears like a gleaming marble. “We have seen it from space as whole and bright and beautiful; we have seen it from the surface of the moon as not very large and somehow vulnerable,” Aldrin wrote in his book. “With all its imperfections, it is a great place to come from and an even greater place to go back to.”

Joan Wong; Photo courtesy of Getty

The Apollo astronauts who had touched the surface of the moon were walking testaments to human achievement. They seemed to ooze unalloyed inspiration. When you ask people to consider the morbid, hypothetical reality of a world without them, most often you hear about that inspiration—and how depressing it would be to lose it.