William Whewell (1794–1866) classified paleontology as one of the historical sciences, along with archaeology, geology, astronomy, cosmology, philology and history itself: paleontology aims to describe phenomena of the past and to reconstruct their causes. Hence it has three main elements: description of past phenomena; developing a general theory about the causes of various types of change; and applying those theories to specific facts. When trying to explain the past, paleontologists and other historical scientists often construct a set of one or more hypotheses about the causes and then look for a "smoking gun", a piece of evidence that strongly accords with one hypothesis over any others. Sometimes researchers discover a "smoking gun" by a fortunate accident during other research. For example, the 1980 discovery by Luis and Walter Alvarez of iridium, a mainly extraterrestrial metal, in the Cretaceous–Paleogene boundary layer made asteroid impact the most favored explanation for the Cretaceous–Paleogene extinction event – although debate continues about the contribution of volcanism.
William Whewell (1794–1866) classified paleontology as one of the historical sciences, along with archaeology, geology, astronomy, cosmology, philology and history itself: paleontology aims to describe phenomena of the past and to reconstruct their causes. Hence it has three main elements: description of past phenomena; developing a general theory about the causes of various types of change; and applying those theories to specific facts. When trying to explain the past, paleontologists and other historical scientists often construct a set of one or more hypotheses about the causes and then look for a "smoking gun", a piece of evidence that strongly accords with one hypothesis over any others. Sometimes researchers discover a "smoking gun" by a fortunate accident during other research. For example, the 1980 discovery by Luis and Walter Alvarez of iridium, a mainly extraterrestrial metal, in the Cretaceous–Paleogene boundary layer made asteroid impact the most favored explanation for the Cretaceous–Paleogene extinction ?event – although debate continues about the contribution of volcanism.