Linneus developed the concept of binomial nomenclature, whereby scientists speaking and writing different languages could communicate clearly. For example Man in English is Hombre in Spanish, Mensch in German, and Homo in Latin. Linneus settled on Latin, which was the language of learned men at that time. If a scientist refers to Homo, all scientists know what he or she means.
William Strata Smith employed by the English coal mining industry, developed the first accurate geologic map of England. He also, from his extensive travels, developed the Principle of Biological Succession. This idea states that each period of Earth history has its own unique assemblages of fossils. In essence Smith fathered the science of stratigraphy, the correlation of rock layers based on (among other things) their fossil contents. He also developed an idea that life had changed over time, but did not overtly state that.
Abraham Gottlob Werner and Baron Georges Cuvier were among the foremost proponents of catastrophism, the theory that the earth and geological events had formed suddenly, as a result of some great catastrophe (such as Noah's flood). This view was a comfortable one for the times and thus was widely accepted. Cuvier eventually proposed that there had been several creations that occurred after catastrophies. Louis Agassiz proposed 50-80 catastrophies and creations.
Jean Baptiste de Lamarck developed one of the first theories on how species changed. He proposed the inheritance of acquired characteristics to explain, among other things, the length of the giraffe neck. The Lamarckian view is that modern giraffe's have long necks because their ancestors progressively gained longer necks due to stretching to reach food higher and higher in trees. According to the 19th century concept of use and disuse the stretching of necks resulted in their development, which was somehow passed on to their progeny.
Today we realize that only bacteria are able to incorporate non-genetic (nonheritable) traits. Lamarck's work was a theory that plainly stated that life had changed over time and provided (albeit an erroneous) mechanism of change.