Everything in the Earth system can theoretically be placed in one of five subsystems: earth, fire, water, air and life. Earth is an open system, which means that energy and matter can be exchanged between several different systems. Since the formation of the planet, key subsystems have continually co-evolved. They are symbiotic in nature and the world would be completely different than it is today if any of these key subsystems were changed or disappeared altogether. These subsystems are frequently divided into different spheres of the Earth, such as the biosphere or the hydrosphere. The Earth's subsystem, often called the geosphere, can be considered as all the parts that make up the mass of the Earth. The Earth has three main layers: the core, the mantle and the crust. However, the lithosphere only represents the upper part of the geosphere, the crust and the upper part of the mantle. These parts contribute to active plate tectonics. The theory of plate tectonics is that the Earth's crust is divided into distinct solid plates that move independently above the mantle. The two major processes of plate tectonics are spreading and subduction. This idea was discovered by Alfred Wegner to support his idea that Earth originally had one large common continent, Pangea, before drifting into the different continents we have today. Plates have three types of boundaries: constructive, destructive and conservative. The constructive limits are mainly the oceanic ridges. They are simultaneously created and destroyed and the crust is moved horizontally in the process. Destructive is when oceanic plate boundaries dip diagonally under a neighboring plate. These neighboring plates are frequently...... middle of paper...... gazine, 227 (5325), 494-499. doi:10.1126Olbers, D. (January 29, 2012). The earth system. Accessed May 11, 2014 from http://www.awi.de/fileadmin/user_upload/Research/Research_Divisions/Climate_Sciences/Climate_Dynamics_new/Publications/earth_system_olbers.pdfPlate Tectonics. (1993). Bloomsbury Guide to Human Thought. Retrieved from http://search.credoreference.com/content/entry/bght/plate_tectonics/0Pollard, D. (ed.). (2010). Hunaity now needs 1.5 Earths. Living Planet Report. Snow, D.J. (August 24, 2001). Fundamental concepts of Earth systems. (University of Oklahoma) Retrieved May 11, 2014, from Earth System Science Education: http://www.esse.ou.edu/fund_concepts/fund_concept_ess.html#FunCon06What is Soil Pollution. (2014). Retrieved May 13, 2014 from Conserve Energy Future: http://www.conserve-energy-future.com/causes-and-effects-of-soil-pollution.php