December 1968- first man vessel to escape earth and go around the dark side of the moon. Earth is a planet that is small and self-contained. Earth"s four spheres are linked as a system through their interactions. Vary on spatial scales from fractions of a millimeter to thousands of kilometers. Have time scales that range from milliseconds to billions of years. The earth system is powered by the sun that drives external processes in the: atmosphere, hydrosphere, and earth"s surface. The earth system is also powered by the. Earth"s interior: heat remaining from earth"s formation, and heat that is continuously generated by radioactive decay, power the internal processes that produce volcanoes, earthquakes and mountains. Best defined as all that surrounds us with which we interact . This can be pretty far-reaching (eg. mars rovers, voyager, etc). From the greek term geo (earth) and logos (discourse). The science that pursues an understanding of planet earth.