While no single energy source is ready to take theplace of fossil fuels, their diminishing availability may beoffset by a regimen of conservation and a combination ofalternative energy sources. This will not solve the problem,however. As long as population continues to grow, conservation isfutile; at the present rate of growth (1.6% per year), even a 25%reduction in resource use would be obliterated in just overeighteen years. And the use of any combination of resources thatpermits continued population growth can only postpone the day ofreckoning.
Controlled thermonuclear fusion is an alluringsolution to the world's energy problems because the"fuel" it would use is deuterium, which can beextracted from plain water. The energy from one percent of thedeuterium in the world's oceans would be about five hundredthousand times as great as all the energy available from fossilfuels. But controlled fusion is still experimental, thetechnology for its commercialization has not yet been developed,and the first operational facility could not come on line muchbefore 2040 (Browne, 1993, p. C12).
But given enough time, today's forests couldbecome tomorrow's petroleum, and given an astronomical sweepof time, the sun itself will burn out. Only in terms of humantime is an energy resource renewable or nonrenewable; and it isnot even clear how human time should be measured. Wood is oftenconsidered a renewable resource, because if one tree is choppeddown, another will grow in its place. But if a tree is taken offthe mountainside rather than allowed to rot where it falls,nutrients that would nourish its successor are removed. If woodis continually removed, the fertility of the forest diminishes,and within a few human generations the forest will be gone.
The short tenure of the human species marks aturning point in the history of life on Earth. Before theappearance of Homo sapiens, energy was being sequestered morerapidly than it was being dissipated. Then human beings evolved,with the capacity to dissipate much of the energy that had beensequestered, partially redressing the planet's energybalance. The evolution of a species like Homo sapiens may be anintegral part of the life process, anywhere in the universe ithappens to occur. As life develops, autotrophs expand and make aplace for heterotrophs. If organic energy is sequestered insubstantial reserves, as geological processes are bound to do,then the appearance of a species that can release it is all butassured. Such a species, evolved in the service of entropy,quickly returns its planet to a lower energy level. In anevolutionary instant, it explodes and is gone.
Resources may be used for their material propertiesor for the energy they contain. Bauxite is a material resource,while coal is an energy resource. Some resources may be usedeither way; wood, for example, may be used as a constructionmaterial or burned in a wood stove, and petroleum may be used tomake plastics or to power cars.
It is not clear how photosynthesis got started,although it is a combination of two systems that can be foundsingly in some life forms that still exist. But blue-green algae,which are among the earliest organisms documented in the fossilrecord, already employed the two-stage process that waseventually handed down to green plants. This is a complexsequence of events that has a simple outcome. Carbon dioxide (ofwhich there was an abundance in the earth's early atmosphere)reacts with water through energy from light, fixing carbon andreleasing oxygen, and a portion of the energy remains captive aslong as the carbon and the oxygen remain apart. Plants releasethis energy when and where necessary to conduct their metabolicbusiness (Starr & Taggart, 1987).
We are caught up, as organic beings, in the naturalprocess through which the earth accepts energy from the sun andthen releases it. There has been life on Earth for at least threeand a half billion years, and over this time there has been aclear and constant evolution in the way energy is used. The firstliving things may have obtained energy from organic moleculesthat had accumulated in their environment, but photosyntheticautotrophs, able to capture energy from sunlight, soon evolved,making it possible for life to escape this limited niche. Theexistence of autotrophs made a place for heterotrophs, which useenergy that has already been captured by autotrophs.