How did citizens of Athens serve their government?

Greek democracy created at Athens was direct, rather than representative: any adult male citizen over the age of 20 could take part, and it was a duty to do so. The officials of the democracy were in part elected by the Assembly and in large part chosen by lottery in a process called sortition.

Explanation:

heat from the core of the earth causes convection currents to occur in the mantle. these currents slowly move the crust around.