Good game!
I do tend to have some problems with trying to place buildings, though. Sometimes, I'll select a building and then click on the Earth, and for whatever reason, the game doesn't recognize that I clicked on an empty tile and the build action cancels. This can be a bit nerve-wracking given the time limit.
As it doesn't seem to matter where on the Earth a building is placed, I suggest that when a player clicks a building type from the build menu, the building just gets placed on a random empty tile.
4/5