Is there a "good" function $f$ that models the temperature of the Earth's crust/mantle/core measured $r$ miles from the center of the earth? By good, I mean a function that strikes a nice balance between being accuracy and being presentable—easy on the eyes. My intent is to use such a function in an activity for my precalculus class. I'm worried such a function doesn't exist, or would be inherently inaccurate because the temperature isn't sufficiently uniform at a fixed distance from the center.
If no such good function exists, we should list the best we've got.