Paleontology or palaeontology is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geologic time, and assess the interactions between prehistoric organisms and their natural environment. While paleontological observations are known from at least the 6th century BC, the foundation of paleontology as a science dates back to the work of Georges Cuvier in 1796. Cuvier demonstrated evidence for the concept of extinction and how the life of the past was not necessarily the same as that of the present. The field developed rapidly over the course of the following decades, and the French word paléontologie was introduced for the study in 1822, which was derived from the Ancient Greek word for 'ancient' and words describing relatedness and a field of study. Further advances in the field accompanied the work of Charles Darwin who popularized the concept of evolution. Together, evolution and extinction can be understood as complementary processes that shaped the history of life.