General Science Chapter 23 Notes

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
• 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
• Erosion forms canyons, caves
• 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
• 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
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
• 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
• 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
• Stalagmite- pillar of minerals on cavern floor
• Sinkhole- weakened limestone can collapse
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,
• Features deposited by wind include sand dunes
and loess deposits
• Dune- deposit formed from windblown sand
• Loess (less)- deposit formed from windblown
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
• 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

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