Geography (from Greek: γεωγραφία, geographia, literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets. The first person to use the word γεωγραφία was Eratosthenes (276–194 BC). Geography is an all-encompassing discipline that seeks an understanding of Earth and its human and natural complexities—not merely where objects are, but also how they have changed and come to be. Geography is often defined in terms of two branches: human geography and physical geography. Human geography is concerned with the study of people and their communities, cultures, economies, and interactions with the environment by studying their relations with and across space and place. Physical geography is concerned with the study of processes and patterns in the natural environment like the atmosphere, hydrosphere, biosphere, and geosphere. The four historical traditions in geographical research are spatial analyses of natural and the human phenomena, area studies of places and regions, studies of human-land relationships, and the Earth sciences. Geography has been called "the world discipline" and "the bridge between the human and the physical sciences".