Sunlight and Life

Abstract

We know that sunlight provides the energy for all living matter, but we probably do not fully realize that it is the only external source of energy for the earth as a whole. If it were not for sunlight, the earth would not only be a dead planet, but would have cooled rapidly as it lost its irreplaceable energy. This loss of energy, which accompanies all processes throughout the universe, is known as ‘entropy’. Newton’s laws state that energy can neither be created nor destroyed, but it can be lost within a system or between systems as in friction between moving bodies. The rate of loss from our earth system is slowed down by the energy of sunlight, chiefly through the agency of chlorophyll. There are other ways in which sunlight can contribute energy which are important in earth history. For instance, finely-divided iron (iron powder), in the presence of sunlight, can catalyze a number of reactions and greatly increase their rate of progress. An old-fashioned method of reproducing plans and drawings was the blue-print process, where an iron salt and sunlight were the necessary materials. Then, of course, there is the use of sunlight in photography, which is really a chemical process activated and accelerated by light. These photocatalytic processes were certainly very important on primitive earth, and probably played a major role in the evolution of living matter.