I'm somewhat surprised he didn't talk about evidence of space-faring ancient civilizations. If humans perish and a new intelligent species comes around in millions of years, they would be able to find stuff we've left on the moon, provided we pepper it all over its surface so as to survive any future meteor impacts.
12 people have been to the moon for about a total human surface time of about 6 days 17 hour mostly spent most of that time spent within a small radius near the six landing sites. and we haven't bothered to go back in over 51 years the number of tablet you would have to bury on the moon for a civilization as advanced as our to find one would be ridiculous you would essentially have to tile the moon in them for us to have guarantee we would have found one of them.
The Lunar Orbiter Laser Altimeter has mapped the lunar surface to, best as I can tell from a quick search, about 1m resolution. So I think a reasonably sized stele or 2001-style monolith would probably have been discoverable at our current tech level.
But we wouldn’t be able to detect human level lunar activity in a million years time.
We can barely detect human activity from 50 years ago when we know exactly where it is.
I think we are More likely to spot ancient Geostationary satellites, which will have drifted away from a perfect circle but should still be noticeable. LAGEOS aren’t in anywhere near that high an orbit but should survive 8 million years. They have a plaque on them designed by Sagan should a future civilisation find them.
How long would it survive as a monolith on the surface before it would appear to be another boulder? How long until it is illegible due to micrometorite abrasions?