"The Moon preserves the early history of the Earth-Moon system" -Carolyn Van Der Bogert

Geological time. Crater counting and whatnot. Anyone who says they understand it intuitively, is lying. You have to let the scale sink in, and then bunches of things you don't know start assaulting your insecurities. This LPI can help. 

One funny thing that lurks in the back of my mind is that if you google 'how old is the surface of the moon', it spits out 4.51 billion. If you change that to Callisto... 4 billion. The odds are great that Callisto is way way older than Luna. Jupiter formed first, Luna formed well after Earth was formed, resurfacing Earth and Theia. That was long after Callisto should have been a thing. Of course the rules are different for each world, but when you go down the list, how old is the surface of Mercury, Iapetus, Hyperion, Ceres, Vesta, even Ganymede, you keep getting 4 billionish. Hell, even Noachian Mars comes to 3.7 (aka first life on Earth) to 4 billion. A billion is a lot, but it's hard to imagine Luna's surface is as old or older than Callisto's, Mercury's surface is extremely-likely much younger than Mercury, so the dating that is being used is clearly inexact. 

And this LPI teaches you all you need to know about exacting. 

• The slide at 7:20 is a pretty on-the-nose guide to the rules of relative dating via crater counting. 
• A very statistical comparison of Luna and Mars comes at 18:40
• At 20:30, somewhat unrelated but I wish I had a URL for the slide/image she keeps referring to. A painting one student did for her. 
• The slide at 25:50 is a geological map of the Apollo 12 site. 
• At 47:30, another great geoplogical map, this time of Aitkin-Basin.
• At 51:30 a marvelous slide comparing of Earth, Luna, Venus, Mercury, and Mars time. Huge payoff. 

This LPI is pretty pointed for an audience composed only of established planetary scientists. So I'll add a shorter LPI that is slightly less so. The two don't overlap much, but combined any dedicated person should understand crater dating much better. 

This one presented by Alexandra E. Huff.