I turned on Proctor's stream and he's discussing periods and so I instantly turn it off.
He really wants to go that far huh?
There are lots of interesting periods. The cambrian, the ordovician, the silurian, the devon, the... actually, things kind of went to shit afterwards. But you get the idea.
There are also the neolithic, the chalcolithic, the bronze age, the iron age... again, things kind of went to shit afterwards, but it was nice while it lasted.
I for one applaud Proctor for talking about these fascinating periods.
There's also the periodic table! Hydrogen, Lithium, Sodium, Potassium, Rubidium, Cesium, Francium...
Unless you're talking about some other, weird kind of periodization that I'm not familiar with.