The Blue Marble: A Single System
Earth is a dynamic planet. Complex and interconnected processes make up the Earth system. This Earth system is made up of smaller subsystems/components: the geosphere is the land, the air is the atmosphere, life is the biosphere and the hydrosphere is all forms of water, including a smaller subsystem of the cryosphere which is ice. These smaller systems interact together and create change. Most events on Earth are going to involve more than one sphere. Let's look at a fairly simple example to begin like volcanoes. Volcano eruptions are events in the geosphere because this is both rock being pushed out from under the surface as well as a change in the surface land itself. Volcanoes also spew a lot of gas and particulate matter into the atmosphere, as well as send hot lava flowing down mountainsides, disrupting the biosphere. Water will condense around that particulate matter in the atmosphere, so now we've involved the hydrosphere as well.
Astronaut photographs taken during the Apollo missions provided full-color images of Earth, and fostered a greater awareness of the need to understand our home planet. Photographs of Earth taken from space show that our planet is a single system. When students observe Earth from this perspective, they can readily see oceans, clouds, and continents that are lit by sunlight, and the energy that supports life on Earth. They will understand that photographs reveal features and events that would be impossible to detect with other means of analysis.
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