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Biogeochemical Cycles - Part 3.docx

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York University
Natural Science
NATS 1840
Carl Wolfe

Biogeochemical Cycles Part III – Energy Flow The Sun (our source of energy) All of the energy available on Earth comes to us from the Sun. Facts about the Sun: Size: 110 x Earth (diameter) Mass: 333, 000 x Earth Temp: 6000^0 (Surface) 10^7 (core) Composition: 90% hydrogen 10% helium Energy Source: Hydrogen fusion The Suns power output varies continuously, but with some regularity. - 11-year sunspot cycle is correlated with solar output. - Brightness (output) is on a long term increasing trend; has probably risen by 25% since the protestant phase - When the supply of hydrogen to be “burned” runs out, the sun will die out and become a white dwarf….. in about 5 billion years. Earth (our home) Distance from Sun: 150 000 000 km Diameter: 12.745 km Mass: 5.9 x 10^24 kg Age: 4.6 billion years Lithosphere: Solid rock crust floating on a liquid interior. Hydrophere: Temperature allows liquid water (71% of surface) Atmosphere: Mainly nitrogen (78%) and oxygen (21%) Solar Energy Received: The Earth intercepts only a tiny fraction of the Suns total power output: An average of about 1360 W/m² (the solar insolation) at the top edge of the atmosphere. Most of this energy is delivered in the form of visible light. The amount of solar energy that reaches the surface and is absorbed by the planet also depends on: - Albedo - Chemical composition of the atmosphere Albedo: o How much power is reflected away from the Earth (or any planet) as a fraction of the incident power. The albedo depends on the nature of the surface and of the atmosphere.  Albedo = (Power Reflected)/(Power Received) High albedo  more power reflected less power absorbed  cooler (all else being equal) Clouds and ice have a high albedo; water, rocks. And forests have a low albedo. Earths average albedo: about 30% Chemical Composition of the Atmosphere A given gas allows light to pass through it at some frequencies but strongly absorbs light at other frequencies. Some atmospheric gases absorb strongly in the same infra-red part of the electromagnetic spectrum in which the surface of the Earth re-emits received solar energy as heat.  Greenhouse Gasses Eg. Water vapor, carbon dioxide, methane, …. Ozone in the upper atmosphere strongly absorbs light at ultra violet frequencies The Greenhouse Effect: Without greenhouse gasses the average surface temperature would be about 33 degrees colder than it actually is. Because of greenhouse gasses in the atmosphere the Earth must raise its surface temperature by about 33 degrees to a
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