[en] The age of discovering new elements by artificial means began in 1937 when element 43, technetium, was discovered. It so happened, however, that technetium was found to occur in certain stars in 1952 and ⁹⁹Tc produced by the spontaneous fission of ²³⁸U was found to occur in uranium-bearing minerals and ores such as pitchblende, in 1961. When the Oklo phenomenon was discovered in 1972, it became also apparent that a large quantity of ⁹⁹Tc existed in nature approximately 1,700 million years ago, when the pre-Fermi reactors were operating on the earth. Results from recent studies on the occurrences of technetium and another man-made element, plutonium, in nature indicate that the solar system began to form about 5,000 million years ago. (orig.)