Prior to the early 1960s, the atmosphere of Venus was believed by astronomers to have an Earth-like temperature. When Venus was understood to have a thick carbon dioxide atmosphere with a consequence of a very large greenhouse effect, some scientists began to contemplate the idea of altering the atmosphere to make the surface more Earth-like. This hypothetical prospect, known as terraforming, was first proposed by Carl Sagan in 1961, as a final section of his classic article in the journal "Science" discussing the atmosphere and greenhouse effect of Venus. Sagan proposed injecting photosynthetic bacteria into the Venus atmosphere, which would convert the carbon dioxide into reduced carbon in organic form, thus reducing the carbon dioxide from the atmosphere.