Final answer:
The order of age of the layers from oldest to youngest, according to the principle of superposition, is 2a (variegated), then 2b (pink), and finally 2c (dark), assuming the variegated layer is the bottommost and the dark layer is the topmost.
Step-by-step explanation:
According to the principle of superposition, in a sequence of undeformed sedimentary rock layers, the oldest layers are at the bottom, with successively younger rocks forming the upper layers. Given the placemarks Problem 2a (variegated), 2b (pink), and 2c (dark), without specific information on their positions relative to each other, we can apply the principle by citing that the variegated layer would be the oldest if it is beneath the pink layer, which in turn would be older than the dark layer if that sequence is observed from bottom to top. Therefore, if arranged from oldest to youngest based on the principle of superposition, it would be 2a (variegated) as the oldest, followed by 2b (pink), and then 2c (dark) as the youngest.