Petroleum is essentially a nonrenewable natural resource, an almost useless mixture comprised of very useful substances. It exists underground in liquid, solid, semisolid, and gaseous states. The name "petroleum" is derived from the Latin words petra and oleum, meaning "rock oil". Created only by nature but exploited by man, petroleum is a nonrenewable resource because people consume it approximately one million times faster than nature can create it. Timber is a renewable natural resource; it can be harvested, replanted, and then reharvested in a few decades. In a sense, petroleum "seeds" are being planted today because the natural processes that create petroleum occur continuously. However, the results cannot be harvested for many millions of years. The petroleum that man "harvests" today was "planted" 30-6,000 million years ago! That is why petroleum is considered nonrenewable.