Understanding Earth as a System
Earth is the only planet we know of that sustains life. A number of factors contribute to making our planet unique and habitable. First, Earth exists within the Sun's zone of habitation, and with the Moon, maintains the precise orbital inclination needed to produce our seasons. Second, life on Earth is critically dependent on the abundance of water in all three phases — liquid, vapor, and ice. Third, carbon, which is the very basis of life on our planet, is abundant, existing in a variety of forms. Carbon makes up about 12% of our bodies’ atoms: we are literally the stuff of stars. In the atmosphere, carbon present as part of both carbon dioxide and methane contributes to the greenhouse effect that keeps the planet’s surface from being permanently frozen. And fourth, Earth's atmosphere and electromagnetic field protect the planet from harmful radiation while allowing useful radiation to reach the surface and sustain life.
These remarkable factors have contributed to Earth maintaining a temperature range conducive to the evolution of life for billions of years. The great circulation systems of Earth — the water cycle, carbon cycle, and nutrients — replenish what life needs and help regulate the climate system. Earth is a dynamic planet; the continents, atmosphere, oceans, ice, and life are ever changing, and ever interacting in myriad ways. These complex and interconnected processes comprise the Earth system.
A number of changing factors, including seasons, vegetation, and incoming solar energy, affect the Earth system. This animation shows how seasonal vegetation changes in the biosphere influence Earth’s carbon cycle.
Examining Connections Among the Parts of the Earth System
Viewing Earth as a system means understanding each of the system’s parts and how they work together. We can learn about the Earth system by beginning with observation. Scientists explore extreme weather events in the context of changing climate, earthquakes and volcanic eruptions in the context of tectonic shifts, and losses in biodiversity in the context of changes in Earth's ecosystems. These studies lead to the exploration and discovery of causes and effects in the environment. As examples, ocean temperatures and circulation are linked to the moderate climate of northern Europe relative to its latitude, annual changes of ozone concentration over Antarctica have been linked to the production and use of industrial refrigerants in the Northern Hemisphere, and the physics and chemistry of the atmosphere directly affect air quality, fresh water availability, and other components of the Earth system.
From space, we can more easily view the Earth system as a whole, observe the net results of complex interactions, and begin to understand how the planet is changing in response to natural and human influences. For example, studies of the Earth system have revealed and quantified the effects of the Sun's solar variability and of the atmosphere's increasing concentrations of carbon dioxide and aerosols on the climate system. The fact that researchers detect not just variability but also trends in the key measures of Earth systems makes it imperative for us to study not just the individual parts, but the workings and interactions of the Earth system as a whole.