Chapter: Earth’s Changing Surface Table of Contents Section 2: Shaping the LandscapeShaping the...

Chapter: Earth’s Changing Surface

Table of ContentsTable of Contents

Section 2: Shaping the Landscape

Section 1: Weathering and Soil

Section 3: Groundwater

Section 4: Geologic Time

• Weathering is an example of physical and chemical processes that involve the interaction of air, water, and rock over time.

• Weathering is the process of physical or chemical breakdown of a material at or near Earth’s surface.

Weathering

Weathering and SoilWeathering and Soil

11

• Factors that influence weathering include the agent, such as water or air, the nature of the material being weathered, climate, and time.

• Forces that can cause mechanical weathering include impact, expansion or contraction of materials, and biological effects.

• Variables that control mechanical weathering include the nature of the material being weathered, climate, and time. Of these variables, time is the least noticeable.

Mechanical Weathering


11

• When water freezes, it expands. This forces the cracks apart and ultimately forces the rock apart.

• This type of weathering is called frost wedging.

Prying Rock Apart


11

• The figure illustrates what happens when a large object breaks apart.

Prying Rock Apart


11

• Rocks can also act as impact agents.

• As a large particle breaks into smaller particles, the amount of surface area increases. More surface area compared to volume increases the likelihood that a material will be attacked by chemical agents.

Prying Rock Apart


11

• The process of chemical weathering forms new compounds and releases elements into the environment.

• Water and oxygen are the key agents of chemical weathering, along with naturally occurring acids.

Chemical Weathering


11

• Soil is a mixture of weathered rock, organic matter, water, and air that is capable of supporting plant life.

• Soil originates from weathering of the bedrock beneath it or from materials transported from another location.

Soil


11

• The figure shows a complete set of horizons, designated as O, A, E, B, C, and R from the surface to bedrock.

• The O horizon, for organic, and the A horizon often are referred to as topsoil.

Soil Horizons


11

• The E horizon is a zone in which finer sediments and soluble materials are transported downward.

• The B horizon collects the materials from above and is usually darker than the E horizon.

Soil Horizons


11

• The C horizon is partially crumbled and weathered bedrock. The R horizon is unweathered bedrock.

Soil Horizons


11

• Climate often is used as a basis to characterize many different types of soil.

Soil Types


11

Soil Types


11

• They are separated according to composition and physical properties.

• The amount of precipitation and the temperature range of a region, together with the type of parent material, affect the soil that forms.

• Soil depletion is a serious agricultural problem in many regions.

Soil Conservation


11

• Soil depletion is most often corrected by the addition of fertilizers containing nitrogen, phosphorous, or potassium.

• Most soil lost to erosion occurs because the vegetative cover has been removed or because the land is overly steep.

Section CheckSection Check

11Question 1

Which is NOT an agent of mechanical weathering?

A. contractionB. expansionC. impactD. oxygen


11Answer

The answer is D. Oxygen is an agent of chemical weathering.


11Question 2

Which mineral, present in rocks, turns a brownish-red color?

A. calciteB. feldsparC. hematiteD. silicon

11Section CheckSection Check

Answer

The answer is C. Hematite is often mined to obtain iron for steel production.


11Question 3

Which horizons combine to form topsoil?

A. A and OB. E and HC. B and CD. C and R

11Section CheckSection Check

Answer

The answer is A. Plants get most of their nutrients from topsoil.

Shaping the LandscapeShaping the Landscape

22

• Erosion is the removal of surface material through the process of weathering.

Erosion, Transport, and Deposition

• Sediment transport is the movement of eroded materials from one place to another by water, wind, and/or glaciers.

• When a transporting agent drops its load of eroded material, deposition occurs.


22

• An important agent of erosion that exerts a downward force on slopes is running water.

Running Water

• In most river systems, small streams called tributaries flow into larger streams, which in turn flow into even larger streams.

Drainage Basins

• All of the land area that gathers water for a major river is the river’s drainage basin.


22

• As surface water flows downhill under the influence of gravity, water erodes the surface, creating its own path or following existing paths called channels.

Channel Development

• When running water slows down, it drops part of the sediment load it is carrying, largest particles first.

Stream Deposits


22

• Floodplains are part of a river, but they are only submerged during floods.

Floodplains

• As the mouth of a stream that empties into a body of water, a fan-shaped sediment deposit called a delta will form.

Deltas


22

• Valley glaciers form at the top, or head, of river valleys in mountainous regions. They move down slope, usually following the path of the preexisting valleys.

Glaciers

• Continental glaciers, which occupy huge land areas, cover all but the highest peaks. Ice moves away in all directions from where it accumulates.


22

• Glaciers become effective agents of erosion as they move either down slope as in valley glaciers or under their own weight as in continental glaciers.

Glaciers


22

• Valley and continental glaciers leave behind deep grooves or striations, which give clues about the direction the ice was moving.

Erosional Features

• Glacial ice exerts pressure to the sides as well creating the distinct and easily recognized U-shaped valley.


22

• Till is composed of random sediment sizes ranging from tiny clay particles to house-sized boulders.

Glacier Deposits

• The large ridges of till that accumulate at the edge of a glacier are called moraines.


22 Wind

• As wind velocity decreases, the load of sediment is dropped.

Wind Deposits

• The shapes and sizes of landforms that form depend on how constant the wind velocity is and on the supply of sediment.

Erosion by Wind• The removal of small particles by wind,

leaving heavier particles behind is called deflation.


22

• Longshore current occurs when waves approach a shoreline at an angle and are refracted.

Wave Action

• The backwash returns to the sea perpendicular to the shoreline.


22

• Longshore currents move sediment along the shore.

Deposition by Wave Action

• Where this current slows, sediments are deposited as offshore sand ridges or bars.

• Sandbars run parallel to the shore.• Spits are sand bars that project into the

water from land and curve back toward land in a hook shape.


22

• Mass wasting occurs when erosion occurs primarily as a result of gravity, whether triggered by an influx of water, by earthquakes, or by human activity.

Mass Wasting

• Wasting erosion caused by mass wasting is dependent upon the type of event and the type of materials involved: slumps, landslides, rockslides, or mudflows.

• Mass wasting events tend to dump their material in disorganized masses.

22Question 1

_______ is the removal of surface material through the process of weathering.

A. DepositionB. ErosionC. SedimentD. Transport


22Answer

The answer is B, erosion.


22Question 2

_______ form when wind moves sand-sized particles into distinct forms.

A. CirquesB. DunesC. GlaciersD. Waves


22 Answer

The answer is B. The shapes and sizes of dunes that form depend on how constant the wind velocity and on the supply of sediment.


22Question 3

Bowl-shaped basins called _______ form by erosion at the start of a valley glacier.

A. arêtesB. bowlsC. cirquesD. horns


22Answer

The answer is C. Valley glaciers form at the head of a river valley in mountainous regions.


The Water Cycle

• Freshwater supplies are constantly being replenished through the water cycle.

GroundwaterGroundwater

33

• A lesser amount enters the cycle through transpiration.

• The energy to power both evaporation and transpiration comes from the Sun.

enters Earth to become groundwater below the surface.

• Infiltration is the process by which water

The Water Cycle


33

Groundwater

• The region near the surface where water can infiltrate freely is the unsaturated zone.


33

• The region below that is the saturated zone.

• The water table is the boundary separating these two zones.

Groundwater Storage

• A rock unit that can transmit water through its pore space is called an aquifer.


33

• A rock that slows or stops infiltration is an aquitard.

Porosity and Permeability

• The combined volume of these shapes defines the material’s porosity.


33

• Permeability is a measure of how well a fluid can pass through a material.

Water Resources

• Wells are holes dug or drilled into Earth.


33

• Much like surface water, groundwater flows downhill.

Obtaining Groundwater

Pollution and Groundwater Resources


33

• Pollutants that are spilled or dumped onthe ground enter groundwater through infiltration, as shown.


Question 1

What is illustrated in this figure?

A. carbon cycleB. nitrogen cycleC. oxygen cycleD. water cycle

33


Answer

The answer is D. The water cycle continually redistributes Earth’s water.

33


Question 2

What is an artesian well?

33

Answer

Wells drilled into aquifers that are under sufficient natural pressure to force water up into a well are called artesian wells.


Question 3

Which is not formed as a result of groundwater?

33

A. cavesB. sinkholesC. springsD. wells


Answer

The answer is D. Wells contain groundwater but they are man-made structures.

33

Time

• Absolute dating is the process of assigning a precise numerical age to an organism, object, or event.

• Relative dating is the process of placing objects or events in their proper sequence in time.

Geologic TimeGeologic Time

44

Absolute and Relative Dating

Uniformitarianism

• Uniformitarianism states that the laws of nature operate today as they have in the past.

• The only changes might be in their rate or scale.


44

Principles of Relative Dating

• Principle of superposition states that the oldest rocks in an undisturbed sequence of rock layers will be at the bottom of the sequence.

• Sedimentary layers always start off as horizontal layers.


44

Original Horizontality

• The principle of cross cutting relationships. states that any rock formation or fault is younger than the rock or feature that it cuts through.

Overlapping Features


44

Unconformities

deposition was absent.

• Unconformities represent gaps in the rock record during which erosion occurred or


44

• A disconformity is an erosional surface between horizontal rock layers.

Unconformities


44

• A nonconformity is an erosional surface between sedimentary rock and igneous or metamorphic rock.

• An angular unconformity is an erosional surface between rock layer segments that intercept at an angle.

Fossils• The remains or traces of organisms found in

the geologic rock record are called fossils.


44

• The process of matching distinctive rock units from different regions is called correlation.

Correlation

Geologic Time Scale

• Paleontologists observe changes in the fossil record and associate them with boundaries of time units.


44

• At these boundaries, fossils of certain life forms are no longer present and new life forms begin to appear.

Absolute Dating

• Some types of atoms are unstable and decay by casting off, or emitting, parts of their nuclei.


44

Radioactive Decay

• The half-life is the time it takes for one-half of a radioactive parent sample to decay to its stable daughter.

Geologic Maps

• Geologic cross-sections represent a vertical slice taken through Earth.


44

• Geologic maps show the horizontal surface distribution of various rock formations.

Basins and Domes

• The principle of original horizontality states that sediments are laid down in horizontal layers.


44

• Compressional forces cause the layers to fold and to dip downward.

Basins and Domes


44

• In basins, the youngest rocks are exposed in the center and tilt or dip inward.

• Domes are essentially the opposite of basins.

Folds• Folding of the crust can also be recognized

on geologic maps.


44

• An upward wrinkle of rock formations is an anticline and a downward wrinkle is a syncline.

wrinkle up or fold. • Rocks subjected to the compression might

Plunging Folds


44

• If the forces are applied unevenly the axis of the fold might plunge back into theEarth, producing a surface pattern of rock like the one shown in the figure.


Question 1

_______ is the process of placing objects or events in their proper sequence in time.

A. Relative datingB. Absolute datingC. Carbon datingD. Fossil dating

44


Answer

The answer is A. When you date events relatively, you know which came first, second, and so on.

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Question 2

Why is Fossil C considered to be between 2.1 and 2.4 million years old?

44


Answer

You could conclude from the rock layers at Location A that Fossil C is between 2.1 and 2.4 million years old, Fossil A is older than 2.4 million years, and Fossil E is younger than 2.1 million years.

44


Question 3

Which time unit of the geological time scale is the shortest?

A. eonB. epochC. periodD. era

44


Answer

The answer is B. An epoch is the shortest time unit of the geological time scale.

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