Excavation is the act of digging and is required to be done with a shovel of some kind. As the skill levels up, you get a higher chance of receiving treasures from what you dig.
Super Ability: Giga Drill Breaker
You can also use Giga Drill Breaker in bursts to speed up digging, at the expense of extra durability wear on your shovel. To counteract this, use diamond shovels. Often when you are past level 350, you'll get at least 1 diamond from a single Giga Drill Breaker, allowing you to repair the shovel whenever durability starts to drop.