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-Introducing our Planet-
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Earth's Energy Imagine what would happen if the sun stopped shining! This disastrous scenario emphasizes the crucial role of solar energy. Our planet relies on a constant input of energy from the sun. Earth receives an inflow of solar energy that is more than 15,000 times the amount of energy consumed by all human societies. This constant flow of solar energy into the planet system provides virtually all the energy to keep our planet warm, drive the cycles of matter and sustain life. If Earth retained all that energy, it would become so hot that it would just boil away. But energy does not stay in any one place. Energy flows away from Earth in the form of heat radiating to outer space. The amount of energy radiating to outer space balances the amount of energy flowing in from the sun. Note the difference between Earth's matter and Earth's energy. With respect to matter, Earth is a closed system. Matter does not enter or leave. With respect to energy, Earth is an open system. Sunlight energy flows in and heat energy escapes.
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