Geology (from the Ancient Greek γῆ, gē, i.e. "earth" and -λoγία, -logia, i.e. "study of, discourse") is an earth science concerned with the solid Earth, the rocks of which it is composed, and the processes by which they change over time. Geology can also refer to the study of the solid features of any terrestrial planet or natural satellite, (such as Mars or the Moon).
Geology may be defined to be that branch of natural history which investigates the successive changes that have taken place in the organic and inorganic kingdoms of nature. It is a science founded on exact observation and careful induction; it may termed the physical history of our globe; it investigates the structure of the planet on which we live and explains the character and causes of the various changes in the organic and inorganic kingdoms of nature.
William Humble in: Dictionary of geology and mineralogy: comprising such terms in botany., H. Washbourne, 1843, p. 104.