Astronaut Footprints on the Moon Will Last 100 Million Years — Here's Why

Prints That Outlast Civilizations

When Neil Armstrong pressed his boot into the lunar regolith on July 20, 1969, he left an impression that will endure longer than any monument, building, or record created by human civilization. The footprints left by the six Apollo missions that landed on the Moon are still there, unchanged. They will almost certainly remain there for at least 100 million years, and possibly much longer.

This longevity is not the result of any special property of the footprints themselves — it is a consequence of the Moon's profoundly different relationship with time and change compared to Earth.

The Moon's Frozen Surface

Earth's surface is constantly changing. Wind erodes rock faces and fills depressions with sediment. Rain dissolves minerals and reshapes landscapes. Biological activity churns soil and deposits organic material. Tectonic activity reshapes continental boundaries over millions of years. On the timescales relevant to surface features like footprints, erosion by wind and water dominates — a human footprint left in a forest or on a beach will typically disappear within hours or days.

The Moon has none of these processes. It has no atmosphere, so there is no wind and no water cycle. It has no liquid water on its surface. It has no plate tectonics, no volcanic activity on a timescale relevant to human footprints, and no biological processes. The Moon's surface is bombarded by micrometeorites and cosmic radiation, and these processes do very gradually disturb the uppermost layer of regolith — but at rates measured in millimeters per million years.

The lunar regolith itself is a fine, powdery layer of crushed rock created by billions of years of micrometeorite impacts. It has a remarkable property: it holds impressions exceptionally well, like freshly packed flour. Under the vacuum conditions of the Moon's surface, fine particles cling together through electrostatic forces. An impression pressed into regolith remains essentially unchanged because there is nothing to disturb it.

What 100 Million Years Looks Like

The 100-million-year estimate for footprint survival accounts for the slow but cumulative effect of micrometeorite bombardment, which gradually gardensizes the uppermost lunar surface at a rate of roughly 1 millimeter per million years. Over 100 million years, this process would slowly blur surface features, eventually softening and then obliterating clear impressions. But "eventually" covers an almost unimaginable span of time.

One hundred million years ago, Earth's continents were in different positions. Dinosaurs had another 35 million years to live. The Atlantic Ocean was narrower than it is today. No human footprints existed anywhere on Earth — our species would not appear for another 99.8 million years. The footprints in the lunar regolith will still be there, essentially unchanged, when timescales of that magnitude have elapsed.

The Apollo footprints are, in a very literal sense, the most durable physical record humanity has ever created. They will outlast every building, every document, every digital record, and every bone. On a geologically quiet surface with no weather, a human boot print becomes, almost accidentally, as close to permanent as anything made by human hands can be.