Where do the white/black letters T K T P stand for?

They line up with the period names.

So from the bottom:

  • P - Permian
  • T - Triassic
  • K - Kretaceous
  • T - Tpaleocene

(no, I have no idea either)

K is indeed for Cretaceous (Kreide in German)
T stands for Tertiary, an old term for the Paleogene
Woah, so I accidentally got to the right answer by making a joke?