Imagery from a NASA spacecraft has revealed that the Moon has shrunk significantly in recent times: indeed, instruments placed by the Apollo astronauts are thought to have recorded the rumbling, crunching sounds of lunar shrinkage carrying on in just the last few decades.
The shrinkage has mostly occurred on a timescale in the hundreds of millions or billions of years.
They rationalize that a "wrinkling" moon is a "shrinking" moon.
That's easy to understand. However, we wonder how "hundreds of millions or billions of years" can equate to "shrinking fast."
Maybe we'll just go back to our whimsical childhood belief that, shrinking or not, the moon is made of green cheese.