Well the Constitution sets forth no specific requirements. However, members of Congress, who typically recommend potential nominees, and the Department of Justice, which reviews nominees' qualifications, have developed their own informal criteria.
It would be the energy source of "fossil fuel" that is formed when organic matter is trapped underground without exposure to air or moisture, since this material is eventually fossilized.
Landowners turned to African slaves as a more profitable and ever-renewable source of labor and the shift from indentured servants to racial slavery had begun.
The best example of the influence of Athenian democracy on later governments is the representative democracy of the United States. One shared quality is the amount of nationalism and patriotism seen in the people and government.