Once in a while, you are confronted with a disarmingly simple experiment, frequently performed years ago, that blows you away with its elegant simplicity.
A simple question is; which of the myriad wavelengths of light that we are exposed to, is reponsible for photosynthesis? To resolve this problem, T. W. Englemann in 1882 placed a long filament containing chloroplasts linearly along the projected spectrum of sunlight from a prism in a solution. He then introduced aerobic bacteria into the system. Where there's photosynthesis, there's generation of oxygen, and the bacteria, by migrating to the red band in the spectrum in large numbers, told convincingly that it is this wavelength of light that is most responsible for photosynthesis. Case closed (almost)
Interestingly, entire species of organisms have created ecological niches for themselves, especially in the depths of the ocean, by exploiting this principle. Sunlight that reaches deep down into the ocean usually contains only a few wavelengths, as the remaining ones have been absorbed by physical elements and biological flora and fauna on the top. By adapting themselves and their proteins and molecular assemblies to absorb exactly these wavelengths, these microorganisms have created a home for themselves where there was none. Before we move on to SETI, let us be enraputured by the intelligence on our own planet, generated through the frenzied agency of 'the blind watchmaker'.
Based on "Lehninger Principles of Biochemistry- 4th edition"