Chapter 23

1. Chapter 23 Earth’s Surface

2. 23.1 Fresh Water • Earth is 71% water • 97% is salt water • 3% is freshwater • Most freshwater is in the form of groundwater- water found underground in cracks and between particles of rock and soil. • Some freshwater is found in lakes, streams, water vapor, and clouds.

3. The Water Cycle • The water cycle is made up of several processes, including evaporation, transpiration, condensation, precipitation, and the eventual return of flowing water to the ocean. • Evaporation- liquid to vapor (gas) • Transpiration- when water vapor is released from the leaves of trees and other plants • Condensation- when water vapor expands and cools, water vapor forms droplets which crystallize at lower temperatures • Precipitation- when water droplets or ice crystals get too heavy, they fall as rain, sleet, snow, hail, or freezing rain

4. Fresh Water • A small portion of Earth’s fresh water is located in the atmosphere, streams, and lakes. Most is located in groundwater and glaciers. • Glaciers- large masses of moving ice and snow on land • Runoff- water that flows over Earth’s surface, goes into streams • Tributary- smaller stream that flows into a larger river • Watershed- area of land that contributes water to a river system (Rocky Mountains to Appalachian) • Saturated zone- region where the pore spaces are entirely filled with groundwater • Water table- top of saturated zone • Permeable- water can pass through • Aquifer- permeable rock saturated with water • Impermeable- water cannot pass through

5. 23.2 Weathering and Mass Movement • Erosion- the process that wears down and carries away rock and soil • Erosion acts through weathering, the force of gravity, and through the movement of streams, groundwater, glaciers, wind, and waves. • Erosion forms canyons, caves

6. Weathering • Weathering is the process by which rocks are chemically altered or physically broken down into fragments at or near Earth’s surface • There are two forms of weathering: mechanical and chemical. They cause rocks to disintegrate or decompose. • Mechanical weathering- process of physically breaking rock into smaller fragments • Abrasion- rocks scrape or grind against one another • Chemical weathering- process in which rock is broken down by chemical reactions, such as water, acid, and oxidation

7. Rates of Weathering • The rate at which mechanical and chemical weathering take place depends on three main factors: temperature, the availability of water, and the type of rock. • High temperature and abundant rainfall lead to a higher rate of weathering. • Limestone and marble rapidly weather.

8. Mass Movement • Mass movement- the downward movement of rock and soil due to gravity • Through the process of mass movement, gravity moves loose material down a slope. • Landslide- rapid movement of large amounts of rock and soil • Mudflow- rapid mass movement of soil and other sediment mixed with water • Creep- soil gradually moves down a slope (caused from ice) • Slump- weak layers of soil or rock suddenly move downslope as a single unit

9. 23.3 Water Shapes the Land • Deposition- the process in which sediment is laid down in new locations, usually by flowing water • Saltation- process of particles bouncing along a stream bottom • A stream’s ability to erode depends mainly on its speed.

10. Features Formed by Water Erosion • Water erosion forms V-shaped valleys, waterfalls, meanders, and oxbow lakes. • V-shaped valley- contains rapids and waterfalls, occur at stream’s source • Flood plain- flat area along a stream that is entirely covered only during times of flood • Meander- slight curving of river, looks like a loop • Oxbow lake- a separate, curved lake formed when sediments cut off river

11. Features Formed by Water Deposition • Features deposited by flowing water include alluvial fans and deltas. • Alluvial fan- when a stream flows out the mountains and onto plains, it slows down, sediments settle, and a fan-shaped deposit of sediment is left • Delta- a mass of sediment deposited where a river enters a large body of water

12. Groundwater Erosion • The processes of chemical weathering causes much groundwater erosion, including the formation of caves and sinkholes. • Stalactite- on cavern ceiling, icicle-like formation • Stalagmite- pillar of minerals on cavern floor • Sinkhole- weakened limestone can collapse suddenly

13. 23.4 Glaciers and Wind • Glaciers form in places where more snow falls than melts or sublimates. • Continental glacier- thick sheet of ice that covers a huge area, such as a continent or large island • Valley glacier- glacier that occurs in a high mountain valley • Plucking- glacial ice widens cracks in bedrock beneath the glacier • Glaciers cause many distinctive features in the landscape, including cirques, horns, U-shaped valleys, and glacial lakes

14. Cirque- valleys formed from valley glaciers • When a glacier melts, it deposits its load of sediment, creating a variety of landforms. • Till- glacial sediment • Moraine- mound of sediment at the downhill end of the glacier and along its sides, formed by till

15. Wind Erosion and Deposition • Wind erodes the land by deflation and abrasion. • Deflation- wind picks up and carries away loose surface material • Abrasion- wind blows sand against other rocks, sandblasting • Features deposited by wind include sand dunes and loess deposits • Dune- deposit formed from windblown sand • Loess (less)- deposit formed from windblown dust

16. 23.5 The Restless Oceans • Salinity- the proportion of dissolved salts in water (35g/kg water) • Light and temperature decrease with depth, whereas pressure increases. • Continental shelf- gently sloping plain forms an apron of shallow water along the edges of most continents • Surface current- large stream of ocean water that moves continuously in about the same path. • Winds blowing across the surface of the ocean cause the continuous flow of surface currents • Deep ocean currents are caused by differences in the density of ocean water • Upwelling- movement of water from the deep ocean to the surface • In upwelling, winds blow warm surface water aside. This allows cold water from the deep ocean to rise and take the place of the warmer water. • Two physical processes, hydraulic action and abrasion, are responsible for much wave erosion • Longshore drift- the process that moves sand along a shore

17. 23.6 Earth’s History • Relative age- of a rock is compared to the ages of other rocks above or below it in a sequence of rock layers • Law of superposition- if rock layers are undisturbed, younger rocks lie above older rocks, and the oldest rocks are at the bottom • Geologists use the law of superposition to determine the relative ages of sedimentary rocks from the sequence of rock layers and the fossils within each layer. • Extinct- no longer exists • Index fossil- easily identified, occurred over a large area, and lived during a well-defined period of time • Absolute age- time that has passed since the rock formed, determined by radioactive dating

18. A Brief History of Earth • Era- major stage in Earth’s history • Period- smaller unit of era • Mass extinction- when many creatures die in a short time • Precambrian time- 4.6 Billion to 544 Million years ago, Earth was formed, one-celled organisms • Paleozoic Era- 544 to 248 Million years ago, clam and worm, fish, flood • Mesozoic Era- 248 to 65 Million years ago, dinosaurs • Cenozoic Era- 65 Million years ago to now, ice age, mammals, humans