The term BRANCH OF SCI is used to refer to the four main branches of science: Geology, Hydrology, Ecology, and Zoology. Geology is the study of the Earth's physical structure and the processes that shape it. Hydrology is the study of water and its properties, circulation, and distribution on Earth and other planets. Ecology is the study of the relationships between organisms and their environment. Zoology is the study of animals and their behavior, physiology, and evolution.