Geography is considered to be the study of place, space and the environment. Geographers explore what places mean, how people shape places, and how places shape our lives. Geographers investigate biophysical environments encompassing terrestrial, marine and atmospheric systems. These investigations include the nature, dimensions and causes of environmental change; the reciprocal relationships between the environment and people; the resources biophysical systems provide and their sustainability. Finally, in their consideration of space, geographers examine how, why and with what effect diverse phenomena vary across the surface of the earth.