And knowing the ages of Moon rocks, which can be computed to within 20 million years, has enabled scientists to establish a baseline that allows them to date geologic features throughout the solar system. The surface of the Earth, one of the solar system’s youngest topographies, is constantly changing, as it is faulted, folded, shaped and reshaped by eruptions, earthquakes and erosion. By contrast, the Moon is as old as it gets.

“It’s hard to wrap your mind around a place where nothing ever happens,” Mr. Allen said. “But the Moon is that place.”

In recent years the rocks have also helped researchers to answer practical questions that have emerged since President Bush’s 2004 proposal to return to the Moon by 2020 and set up a permanent outpost. Planners are using the rocks to study the pernicious effects of regolith on machinery and astronaut health. They are learning how to extract oxygen and other vital elements from lunar rocks and soil. And they need to understand how to shield living spaces from the deadly radiation that eternally pounds the lunar surface.

The samples  2,200 of them  are kept in nitrogen-filled boxes in a stainless steel vault on the second floor of the 14,000-square-foot repository, and are transferred to other parts of the lab in airlocks. Technicians prepare shipments in glove boxes containing sterile tools and containers.

The samples are numbered and sorted by expedition. All of the Apollo landings, beginning with Apollo 11’s historic mission in 1969 and ending with Apollo 17 in December 1972, were at equatorial sites, but terrain differed each time and the samples reflect the differences. The genesis rock was collected by Apollo 15 astronauts near Hadley Rille at the border between a lowland “sea,” or mare, and the lunar highlands.

Image Carlton C. Allen with the genesis rock in the lunar lab. Credit... Michael Stravato for The New York Times

The arrival of the first Moon rocks in 1969 was eagerly anticipated by scientists. “We had no idea what the Moon was made of,” Mr. Allen recalled, and the first two decades of research focused on basic questions  the age and composition of the Moon rocks and the origin and evolution of the Moon’s geology and salient topographical features.