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The energy we receive for life on Earth comes from primarily from the sun.At 93 million miles or 150 million kilometers from the sun, Earths global mean temperature is well suited for life.The atmosphere, through the greenhouse effect, is also essential for maintaining Earths Temperature. Even at our present position from the sun, if earth had no atmosphere, it would much colder than at present.Venus is much hotter than Earth not only because it is closer to the sun but also because its atmosphere is composed primarily of carbon dioxide, a potent greenhouse gas. Well learn more about the greenhouse effect later.2Early atmosphere~4.5 billion years ago Mostly Hydrogen and HeliumEscaped into space

Outgassing of water vapor and CO2 created a secondary atmosphere with some nitrogen

As liquid water formed the oceans and CO2 was removed from atmosphere The atmosphere became dominated by nitrogen.

~ 2 billion years ago oxygen increased in the atmosphere because of plant life and photosynthesis. This allowed for the formation of the stratospheric ozone layer which further enhanced conditions for life on Earth.78 % Nitrogen N220.95 % Oxygen O20.93 % Argon Ar

H2O 0 to 4 %

Carbon Dioxide CO2 0 to .037 % (or 370 ppm)Methane CH4 1.8 ppmNitrous Oxide N2O .3 ppmOzone 0.04 ppm or 40 ppb)Aerosols (particles) highly variableClick to listen

Click to listenIt is important to realize that water vapor is invisible. The clouds you see in this photo are compose of liquid water droplets formed as water vapor condenses into liquid. When we breathe out our breath contains lots of water vapor. This water vapor can becomes visible water drops if we breath onto a cool piece of glass.By far invisible water vapor is the most important atmospheric greenhouse gas.5

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Click to listenCarbon Dioxide is the second most significant greenhouse gas.

Click to listenMethane is another important greenhouse gas. Preindustrial levels were less than half of what they are today. In the early part of the past decade it looked as if methane was stabilizing. More recently is has started to increase again.

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Low densityHigh density

Click to listenMass - quantity of matter

Click to listenWeight = mass x gravity

Click to listenDensity = Mass /volume

Click to listenPressure = Force /Area

300 lbs or 4 sq inches=75 psi

100 lbs or 0.25 sq inches=400 psi

Click to listenStandard Sea Level pressure is:

1 Atmosphere

14.7 psi

1013 milli bars

Click to listenAir Pressure (& density) drop by 1/2 for every 5.5 km altitude gain.

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Click to listenLapse Rate is the temperature drop per kilometer height increase

Typically about 6 C/km = 6 C/1000m

Or

About 3 F/1000 ft

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Synoptic Weather map

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