GEF

Unit 4   |  The Global Ecosystem 91 4.2  The Earth as a System Our planet is connected by interdependent Earth systems , including the atmosphere (gases), the hydrosphere (water), the biosphere (life), and the lithosphere (rock). An under- standing of Earth systems and how they interact is crucial to understanding sustainability. The carbon cycle is an important example of how Earth sys- tems are linked. It also illustrates how human activity impacts these systems. 1. Carbon is found in all four of Earth’s systems. Carbon is found in Earth’s atmosphere system as the gas carbon dioxide. In the atmosphere, CO 2 is responsible for the green- house effect, which traps heat that would otherwise be lost to space. Without atmospheric CO 2 and the greenhouse effect, the average temperature of Earth would be about zero degrees F (-18°C) instead of its present 57°F (14°C). The carbon cycle describes the transition of carbon dioxide on Earth. EARTH SYSTEMS Large-scale realms of the Earth that are interdepen- dent with each other, such as the atmosphere and the oceans. ATMOSPHERE The gases that surround the Earth and form a protective layer from external radiation and temperature extremes. HYDROSPHERE All liquid and frozen surface waters, groundwater, and vapor on the Earth. BIOSPHERE The zone of life on Earth. LITHOSPHERE The Earth’s crust and upper mantle.