What happens if the ground of a PCB touches the earth?
Your anti-static wrist has a 1 Megohm resistor. This will allow the potential to equalize slowly without any damage or spark. If you carry a PCB, and then you must place it on a grounded surface, touch the surface with your other hand before you set down the PCB. Don't let the PCB be the first thing to contact a grounded conductor. If you hand a PCB to another person, touch the person first (shake hands or fist bump or whatever), then transfer the PCB.
Soldering stations usually have anti-static mats, and you are supposed to wear the anti-static wrist band when you solder, also. So the PCB should be at earth potential prior to the soldering tip touching the work piece.