Chapter 23 Earth’s Surface

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.

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

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

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

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

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.

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

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.

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

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

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

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

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

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

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

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

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