
Natural resources such as , (crude oil) and take thousands of years to form naturally and cannot be replaced as fast as they are being consumed. It is projected that fossil-based resources will eventually become too costly to harvest and humanity will need to shift its reliance to such as solar or wind power. An alternative hypothesis is that carbon-based fuel is virtually inexhaustible in human terms, if o.

Astronomers sometimes divide the Solar System structure into separate regions. The includes Mercury, Venus, Earth, Mars, and the bodies in the . The includes Jupiter, Saturn, Uranus, Neptune, and the bodies in the . Since the discovery of the Kuiper belt, the outermost parts of the Solar System are considered a distinct r.