Not really a great insulator as such but it’s not a superconductor either. The earth is in space, and space is cold so while heat is conducted slowly through solid rock towards the surface, that heat is then able to both convect and radiate away.

Yes it is very weird. It highlights the fact that there is no such thing as absolute position, only relative position.

The question asked was about the strength of gravity exerted by one planet, so a slightly more apposite formula is the one for the gravitational acceleration felt by an object of any mass in free fall:

g=G.M/r²

i.e. it’s independent of the mass of the other object.

For any given gene the mutation rate will vary depending on how tightly “conserved” (I.e. constrained by necessity) that type of gene is. For instance the genes controlling the creation of certain cytochrome molecules used in cellular respiration are so highly conserved that they haven’t changed since our last common ancestor with the pea plant. Whereas genes controlling something superficial like skin pigmentation or shape of the pinna may diverge much more freely.