The soil that is closest to the earth’s surface contains HUMUS (not like the hummus you eat!), which is organic mat ter from decayed animals and plants. Humus is essential for plant growth: The nutrients from decomposing animals and plants get cycled back into the environment through humus in the soil. Erosion When you build a sand castle and waves wash it away, your sand castle is eroded by the waves. EROSION is the removal of weathered material.
The four main forces of erosion are: 1. WATER: When it rains, the force of gravity pulls water down across the earth. GULLIES, RIVERS, and STREAMS: The traveling water is called RUNOFF, or WATERSHED, and it forms gullies (like a gutter or drain in the earth) where it carries sediment away. Over time, these gullies can form large rivers.
The faster the water moves, the heavier the particles it can transport. SHEET FLOW: The rain falling on a sloped surface, like a hill, forms a sheet of water, which carries away loose sediment in a process called SHEET EROSION. It’s like a giant waterslide. ICE: Huge masses of ice, called GLACIERS, move across the earth’s surface, carrying away chunks of rocks and scraping rock surfaces, wearing them down and creating grooves.
Glaciers are like rivers of ice that slowly bulldoze their way down a mountain. GRAVITY: Of course, gravity is the force that carries water and glaciers downhill. But gravity doesn’t only cause water to move, it can also cause erosion through MASS MOVEMENT, or the erosion of land. Some examples are ROCK SLIDES and MUDFLOW.
rock slide mudflow when rocks come Like a rock slide, but with mud: loose and bounce and Sediment that accumulates water slide down a hill or forms mud and gets heavier. The mountain added water weight pulls the mud downhill, creating a mudslide. WIND: Wind blows loose rock and sand against other rock surfaces, and can transport these particles across a landscape. 255 DEPOSITION DEPOSITION is the process of water or wind depositing, or dropping, sediment.
Some examples are: DELTAS: triangular areas of nutrient-rich sediment deposited by rivers FLOODPLAINS: areas of sediment that are created when nearby rivers or streams flood and deposit sediment MORAINES: debris deposited by glaciers TALUS DEPOSITS or SCREE SLOPES: broken rocks that have fallen from nearby cliffs DUNES: hills of sand built by wind or water TOPOGRAPHIC MAPS TOPOGRAPHIC MAPS can contain information about where highlands, like mountains, or lowlands, like valleys, are located. The land’s height above sea level is its ELEVATION. The elevations are presented with CONTOUR LINES, which are lines that connect points of the same elevation. topography the shape and terrain features of land 256 w CheckYour Knowledge 1.
Explain the difference between mechanical and chemical weathering. Give two examples of mechanical weathering. Give two examples of chemical weathering. What are the different ways water erodes land? 6.
Explain how ice wedging works. Give a real-life example of chemical weathering. What do topographical maps tell us? 9. How does a floodplain form? 10.
Explain the differences among weathering, erosion, and deposition. How do glaciers move material? answers 257 Check Your ANSWERS 1. Mechanical weathering is physically breaking rocks down. Chemical weathering is when rocks are broken down by chemical reactions.
Any two of the following: ice wedging, plant and animal action, abrasion, release of pressure, or thermal stress 3. Any two of the following: natural acids, plant acids, or oxidation 4. Humus is organic matter from decayed animals and plants. Flowing water creates rivers and gullies, streams erode land, and sheet erosion pulls down dirt from land.
Water in cracks freezes. As water freezes, it expands, widening the crack. Rust forming on iron-rich rocks 8. The shape of land and its terrain features 9.
A floodplain is created when a nearby river floods and deposits sediment. Weathering is when rocks are broken down into smaller pieces. Erosion is the removal of weathered rocks. Lastly, deposition is the dropping of sediment.
As glaciers move, they scrape the earth’s surface and transport rocks, sediment, and other materials. #7 has more than one correct answer. 258 Chapter 25 THE EARTH’S ATMOSPHERE AND WATER CYCLE The EARTH’S ATMOSPHERE The earth’s ATMOSPHERE, which is a thin layer of gas surrounding the planet, is what allows life to exist on Earth. The atmosphere is like the earth’s blanket : It absorbs and traps just the right amount of heat from the sun to keep our planet at a livable temperature.
The atmosphere also protects us against harmful radiation and has gases, such as oxygen and carbon dioxide, which people, animals, and plants need to survive. 259 WHAT WE OFTEN REFER TO SIMPLY AS “AIR” Composition The atmosphere is made of both gases and AEROSOLS, which are solid particles. The gases are: 78 percent nitrogen 21 percent oxygen 1 percent other gases like argon, carbon dioxide, water vapor, carbon monoxide, OZONE (a colorless, toxic gas), methane, hydrogen, etc. Each of these gases plays an important role in the atmosphere.
WATER VAPOR is like a very fine mist that can create clouds and weather. Ozone absorbs ultraviolet (UV) radiation from the sun. Plants use carbon dioxide for essential processes, and carbon dioxide is also a GREENHOUSE GAS, which means that it traps heat from the sun, warming the earth. Currently, the earth’s atmosphere has too much heat- trapping carbon dioxide, which is causing our overall climate to warm and change-a phenomenon called global warming, or GLOBAL CLIMATE CHANGE.
Along with gases, there are particles in the atmosphere called aerosols. These particles include salt evaporated from oceans, dust from the ground, pollen from plants, ash from volcanoes, acids, and other particles from human pollution. Aerosols can affect the weather and climate because they reflect and absorb sunlight. 260 Atmosphere Layers THE THICKNESS OF EACH LAYER The atmosphere has five layers (listed from VARIES, SO THESE closest to farthest from the ground): ARE AVERAGES.
TROPOSPHERE (0–16 kilometers from the ground) • The layer closest to Earth (the tallest mountains are only about 8 kilometers high) • Contains most of the weather • Contains most of the air molecules • Heated by the warmth of the earth’s surface—so the higher you go in the troposphere, the colder it gets 2. STRATOSPHERE (16–50 kilometers from the ground) • Layer above the troposphere • Most large planes fly here. • The ozone layer is located at the ozone layer a layer of gas in the top of the stratosphere. atmosphere that • Because the ozone, which is located protects humans and high up in the stratosphere, animals from harmful absorbs UV radiation from the sun, UV rays from the sun it gets warmer as you get higher.
MESOSPHERE (50–80 kilometers from the ground) • Temperatures here drop drastically because it contains little ozone and The prefix meso matter to absorb heat.” • Meteors that enter our solar system The meso sphere is the middle layer of usually burn up here. (A “shooting star” the atmosphere. is a meteor burning in the mesosphere. THERMOSPHERE (90–500 kilometers) • The hottest layer in the atmosphere • Filters out gamma rays and X-rays from the sun 5.
EXOSPHERE (500–10,000 kilometers) • The outermost layer of the atmosphere • Has almost no matter, and eventually Exo is a Greek suffix that fades into space means “outside.” The exo sphere is the • Satellites orbit the earth outermost layer. in this layer. NOT TECHNICALLY A LAYER; IT RESIDES WITHIN THE BONUS CATEGORY: IONOSPHERE OTHER LAYERS. • An ion is a charged particle—the ionosphere is made of a layer of charged particles.
RADIO RECEPTION IS BETTER AT NIGHT • This layer absorbs the sun’s AM radio waves, BECAUSE OF THE while at night, in the sun’s absence, the IONOSPHERE! ionosphere reflects radio waves from city to city. Ozone Layer The oxygen we breathe is made of two oxygen atoms bonded together; ozone is made of three oxygen atoms bonded together. The ozone layer, which is in the stratosphere, protects us from the sun’s UV rays- the same rays that cause sunburns and skin cancer. THE OZONE HOLE IS NOT WHAT IS CAUSING GLOBAL CLIMATE CHANGE, ALTHOUGH MANY PEOPLE GET THESE CONFUSED.
262 IONOSPHERE Use this mnemonic to remember the order of layers in the atmosphere: Test Scores Make Teachers Excited. Save the ozone layer Chlorofluorocarbons (CFCs), chemicals used in some refrigerators and in aerosol spray bottles (like hairspray), damage the ozone layer. Our use of CFCs has caused a hole in the ozone layer above Antarctica. You can see the ozone layer’s development at ozonewatch.
263 Pressure Changes Because the force of gravity pulls molecules to the earth’s surface, most of the air molecules are concentrated close to that surface, so air pressure is greatest in the troposphere. Air pressure decreases as you go higher in the troposphere. It gets harder to breathe when you are in high altitudes because air pressure decreases with altitude, so there is less oxygen in the atmosphere. Mountain climbers spend months at high-altitude camps in preparation for climbing a big peak in order to get used to the different air conditions.
Temperature Changes Like pressure, temperature changes with altitude. The earth’s surface is heated by the sun. The troposphere, in turn, gets most of its heat from the earth’s surface. So in the troposphere, the temperature decreases as you travel farther from the ground.
The stratosphere is heated by the ozone layer, which absorbs a lot of radiation and heat from the sun. Because the ozone layer is located at the top of the stratosphere, the temperature increases as you travel higher. The part of the mesosphere closest to the ozone layer gets the most warmth. Because the ozone layer is close to the bottom of the mesosphere, temperatures decrease as you travel higher.
264 OZONE Temperatures in the thermosphere and exosphere also increase as you travel farther from the earth’s surface, although there are so few molecules it wouldn’t feel “hot.” WATER CYCLE Water gets cycled through the land and the atmosphere through the WATER CYCLE. The water cycle consists of evaporation, transpiration, condensation, precipitation, and runoff, repeated over and over again: EVAPORATION is when a liquid changes to vapor through heating. The sun’s rays heat water in oceans and on the ground, transforming it into water vapor that rises into the atmosphere. Plants also release water vapors into transpiration or the air through TRANSPIRATION evapotranspiration or EVAPOTRANSPIRATION.
a plant releasing water vapor into the environment CONDENSATION is when a gas changes into a liquid through cooling. After water has been evaporated into the air, the air cools down and the water molecules clump together to form tiny droplets of liquid water, forming clouds. 265 PRECIPITATION is when water droplets in clouds get large and heavy and fall from the atmosphere back to Earth—as rain, snow, hail, and sleet. When precipitation falls on the ground, it gets absorbed and funneled into streams and rivers that eventually flow back into the ocean.
Water flowing above ground is called runoff, while water flowing below the surface is called groundwater. Warm air passes over the ground and the ocean, evaporating water back into the atmosphere, beginning the process all over again! So water never enters or leaves our ecosystem- it just gets cycled through different forms. Most of the gas in the atmosphere is ________ and ______. As you travel higher in the troposphere, temperatures ________.
The hottest layer in the atmosphere is the thermosphere, although it wouldn’t feel hot because the _________ are so few and far between. Describe the stratosphere. Most weather is located in the _ _ _ _ _ _ _ _ _ _ _. What does the ozone layer protect us from? 7.
The air pressure _________ as you get closer to the earth’s surface. Describe the mesosphere. Describe the water cycle. answers 267 Check Your ANSWERS 1.
The stratosphere is above the troposphere. It is where planes fly.