Since organisms depend on a number of elements in addition to those contained in organic compounds, the biological evolution may be studied from the viewpoint of the interaction between inorganic elements and the biological systems, i.e., bioinorganic chemistry. The bases of this approach [1] are (1) differential requirements for elements (different organisms may need different elements), and (2) the historical variation in the availability of elements on the earth, especially n the hydrosphere. One fundamental assumption is that an organism which would require a specific element would not evolve (come into being) before that element becomes readily available to it. The historical variation in the availability of elements depends mainly on the oxidative state of the hydrosphere, which in turn may be controlled by the oxygen content of the atmosphere. The latter is believed to have changed substantially during the course of earth's history, from a very low value at the beginning to the rather value in the present atmosphere. Accordingly the oxidation states of elements could have been altered throughout. These principles are illustrated here by the case of copper. Copper, because of its rather high reduction potential (E for Cu(II)/Cu(I) = +0.34 v at pH = 0), seems to have been unavailable (in the soluble Cu(II) form) until quite late in the history of the earth. An estimate [1, 2] puts the time when Cu(II) became readily available in the hydrosphere to be around 1.7 billion years ago and thereafter. It is inferred that copper was not utilized in the organisms that developed earlier than that time. Most of the copper proteins and enzymes of today are found only in uekaryotes, the more advanced form of organisms. Such proteins include hemocyanin, tyrosine, ceruloplasmin, ascorbate oxidase, laccase and dopamine-beta-hydroxylase. Azurin is found in some aerobic pro-karyotes, whereas plastocyanin and cytochrome c oxidase (copper-dependent) are found in a limited number of cyanobacteria and aerobic bacteria, in addition to most eukaryotes. Superoxide dismutase (SOD) in prokaryotes and mitochondria contain either iron or manganese, while SOD in the cytoplasm of most eukaryotic cells is a Cu,Zn enzyme. It may then be inferred that these organisms, some prokaryotes and most eukaryotes, that contain Cu-dependent proteins could have evolved later than 1.7 billion years ago. The biological evolution is now studied (among other things) from sequencing of homologous proteins and polynucleotides of different organisms. The information obtained from bioinorganic studies of different elements (such as outlined here) could be complementary to the molecular evolutionary studies in elucidating the biological evolution.