Probably ice. Ice that falls into the entrance and then sublimates has a good chance of moving to perpetual darkness regions and to stay there. Factor a couple billion years and you probably will have a decent amount.

Now imagine there is some simple biology happening from the time the Moon had some atmosphere, in caves sealed billions of years ago.

somebody already did image that..

  https://en.wikipedia.org/wiki/The_Lotus_Caves

I wasn't thinking about complex lifeforms, as there isn't enough energy in those dark caves to power anything complicated, but some rock-eaters could have thrived there.

It's remarkable the Moon has so many interesting stories waiting to be uncovered.

The missing back story to Apollo 18!

Really cool rocks, though.

I would love to know the rough cost to send a probe to the moon.

If only there were terrorists on the moon, then no one would worry about the cost.

There probably wouldn't be a moon left either

You just made me start rooting for Iran’s space program.