1578
Sea Level
(imgs.xkcd.com)
Alt text: They're up there with coral islands, lightning, and caterpillars turning into butterflies.
Maybe‽
We don't have much of a basis for comparison outside of our solar system just yet, but we should have better data soon.
And it being "normal" would just make it more science fictiony. =D
We probably won't have better data soon. Actually resolving planets directly is incredibly far out of reach. Measuring their core is implausible.
The core, no, but detecting the effects of a magnetic field are not out of the question.