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Chapter 37 Earth’s atmosphere and oceans. Earth’s Oceans Moderate Land Temperatures. Water has a large heat capacity. So earth is slow to heat up or cool down; to cool down, water has to transfer heat to its surroundings/water absorbs a great deal of heat before its temperatures increase.
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Earth’s Oceans Moderate Land Temperatures • Water has a large heat capacity. • So earth is slow to heat up or cool down; to cool down, water has to transfer heat to its surroundings/water absorbs a great deal of heat before its temperatures increase. • Water’s large heat capacity is why land bordering on the ocean have moderate temps. • Compare seasonal variations: San Francisco, Ca stays moderate year-round while Witchita, KS (on the same line of latitude but not bordering on an ocean) experiences major seasonal changes.
Evolution of the Earth’s Atmosphere and Oceans • The ancient atmosphere did not have free oxygen. • It was mostly H & He, with ammonia and methane. • Volcanoes expelled other gases: 80% water vapor, 10% CO2, and 5% N. • Blue-green algae and stromatolites put O2 in the atmosphere thru photosynthesis; took in CO2 and released O2. • Ozone (O3) was formed in our atmosphere; ozone filters ultraviolet radiation. • As Earth cooled, water vapor condensed to form oceans.
Components of the Earth’s Atmosphere • At sea level, the air is dense and warm. • It gets thinner and cooler as elevation increases. • The atmosphere doesn’t have a defined top- it just gradually thins to outer space. • Air has weight. It exerts pressure. The pressure decreases with increasing height. • Gases include: 78% N, 21% O, 1% Ar, Ne, He, CH4, and H2.
Vertical Structure of the Atmosphere Exosphere Thermosphere Mesosphere Stratosphere Troposphere Ionosphere: between upper mesosphere and thermosphere
Solar Energy • Why are the Earth’s equitorial regions always warmer than the polar regions? • Tilt Rays • High noon at the equator is direct light • High noon at the poles is light at an angle
The Seasons • Seasons are caused by variations in the angle of the sun’s rays striking the Earth’s surface. • Earth follows an elliptical path around the sun; the Earth is farthest from the sun when the Northern Hemisphere experiences summer! • It’s not the distance from the sun- it’s the angles of the rays that is responsible for the earth’s surface temperatures.
Tilt Rays also affect the length of daylight. • That’s why at the arctic/antarctic circles they experience 6 months of continuous daylight and 6 months of continuous night. • Summer solstice: longest daylight, June 21/22 • Winter solstice: shortest daylight, Dec. 22/23 • Vernal Equinox: Mar. 20/21 • Autumnal Equinox: Sept. 22/23 • In each equinox, the light to day hour ratio is equal
Terrestrial Radiation • The sun emits “solar radiation.” • It enters the atmosphere. • It gets absorbed by the land. • The heat gets remitted back into the atmosphere = “terrestrial radiation.” • Therefore it’s not the solar radiation that directly warms the lower atmosphere, it’s the terrestrial radiation. • The temperature of the earth depends on the amount of solar radiation that comes in versus the terrestrial radiation that goes out.
The Greenhouse Effect & Global Warming • Terrestrial radiation gets absorbed by atmospheric gases: H2O vapor and CO2. • This the greenhouse effect. It’s good. It keeps earth from freezing. • As carbon levels rise in the atmosphere, more heat gets trapped so the average temperature of the earth also increases. • Ways in which carbon gets added to the atmosphere are natural and by man: volcanic eruptions, industries and factories burning coal/oil, burning fossil fuels.
