Praxis Review for Science.ppt by wangnuanzg


									 Praxis Review for
   Earth Science
Frank H. Osborne, Ph. D.

3: Earth Materials and
   Surface Processes
          Earth Materials
•A mineral is a naturally occurring substance
with characteristic physical and chemical
•Nearly all rocks are composed of minerals.
•Polymineralic rocks are composed of more
than one mineral, ex. granite.
•Monomineralic rocks are composed of only
one mineral, ex. limestone.
          Earth Materials
Mineral Composition
Minerals are composed of elements. Some
minerals contain only one element (copper,
sulfur and graphite (carbon)).
•Most minerals are made up of only a few
•Oxygen is the most common element by
weight and volume.
•Silicon is second most abundant by weight.
          Earth Materials
Properties of Minerals
Characteristics of minerals include:
•cleavage and fracture
          Earth Materials
Properties of Minerals
Differences in properties are used to
categorize and identify minerals.
•The acid test is the use of hydrochloric acid
on limestone. The result is that bubbles of
CO2 are liberated.
•Minerals have a characteristic crystalline
structure, in many cases the silicon-oxygen
            Rock Formation
The Rock Cycle relates the three types of
          Earth Materials
The Rock Cycle
•Any one rock type can change into any other
rock type.
•There is no preferred direction of movement
of materials in the rock cycle for any one
mass of material.
•There is no exact point of separation
between the rock types.
          Earth Materials
The Rock Cycle
•Sedimentary rocks often contain sediments
or fragments which have varied origins.
•The composition of some rocks suggests that
the materials (sediments or minerals) in the
rock have undergone multiple
transformations (changes) within the rock
    Weathering and Erosion
Weathering is the breakdown of rocks to
form particles called sediment.
•Physical weathering is the breakdown of rock
without chemical changes
  –Freezing and thawing (frost action)
  –Thermal expansion and contraction
•Chemical weathering is the breakdown of
rock by chemical action
  –oxidation, hydration, solution by acids
    Weathering and Erosion
Factors affecting weathering are:
•Exposure--more exposure means faster
•Particle size--the smaller the particles, the
greater the surface area
•Mineral composition--some minerals (quartz)
are more resistant to weathering than others
(mica and feldspar)
•Climate--warmth and moisture enhance
    Weathering and Erosion
Soil is a product of weathering.
•Residual soil forms from the weathering of
rocks nearby.
•Transported soil is brought in by erosion.
Soil layers develop over time. The soil
composition generally tends to reflect the
composition of the rocks below.
    Weathering and Erosion
Soil Profiles
•A soil horizon is a vertical layer of soil with
certain characteristics. For example, the top
layer of soil usually is rich in organic
•Lower horizons result from weathering. The
horizon just above the bedrock will contain
partially weathered rock.
•There is a subsoil layer just below the topsoil
    Weathering and Erosion
Soil types
•Residual soil is formed from the rocks or
regolith below the soil layer. These soils
usually relate to the underlying rocks. They
can be sandy, clayey or loamy if they have
much organic material.
•Transported soil is one that has been move
into an area from someplace else by erosion.
    Weathering and Erosion
Erosion is the process by which sediments are
obtained and transported.
•Transporting agents include water (streams),
glaciers, waves, density currents in water,
wind, and people.
•Driving forces include gravity and change of
potential to kinetic energy.
    Weathering and Erosion
Stream Erosion
Stream water carries sediments.
•Dissolved minerals are carried in solution.
•Small solid particles are carried in
•Large solid particles are moved by rolling or
bouncing along on the bottom of the stream.
    Weathering and Erosion
Stream Erosion
The ability to carry sediment depends on
velocity. The velocity depends on the
gradient (slope) and discharge (volume) of the
•Stream velocity varies. On a curve, it is fast
on the outside and slow on the inside.
    Weathering and Erosion
Stream Erosion
    Weathering and Erosion
Wind Erosion
•Wind causes erosion. When wind carries
sediment, it forms dunes.

Glacial erosion
•A glacier can carry large amounts of dirt.
•When the glacier stops moving, it drops the
dirt forming a moraine.
    Weathering and Erosion
Glacial Erosion
An example is the Hubbard Glacier in Alaska
    Weathering and Erosion
Glacial Erosion
•There is a moraine
in New Jersey left
over from the last
ice age. The glacier
also formed Long
Deposition is also known as sedimentation.
Deposition occurs when the velocity of water,
wind or other erosional system decreases.
Deposition depends on:
•Particle size--heavier particles sediment
•Shape--spherical particles sediment faster
•Density--denser particles sediment faster
Rock layers are formed by sediments. The
size of the particles determines the rock type.
Boulders, gravel, pebbles--conglomerate
Colloids, clay--shale
Colloids, chemical sediments--limestone
Deposition by moving water
Deposition by moving water
•When a river enters the ocean, the velocity
•Sediments are deposited and form a delta.
•An example is the Mississippi River Delta.
         Rock Formation
Rocks are the solid material that make up the
Earth. There are three types:
•Sedimentary Rocks--formed by solid
sediments weathered from pre-existing rocks
•Igneous Rocks--formed by cooling of liquid
•Metamorphic Rocks--formed by
transformation of igneous or sedimentary
rocks by reheating
          Rock Formation
Formation of sedimentary rocks
•Cementation--larger particles are cemented
by minerals precipitated out of the water
•Compression--very small particles are
compressed by immense weight of water and
sediment layers about them
•Chemical action--ionic materials precipitate
out of the water
•Biological processes--precipitation of
minerals by biological organisms
          Rock Formation
Properties of sedimentary rocks
•Particles of sedimentary rocks resemble the
sediments they came from
•Some contain a mixture of sediments, others
a single type of sediment
•Some sedimentary rocks are of organic
origin (example: coal)
•Sedimentary rocks form layers called strata
•Sedimentary rocks frequently contain fossils
           Sedimentary Rocks
Identifying sedimentary rocks
• There are three major groups of sedimentary
• Detrital rocks form from sediments washed
  in by water, such as gravel, sand and mud.
• Chemical sedimentary rocks have crystalline
  texture: limestone, dolostone, gypsum, salt
• Biochemical sedimentary rocks: clastic
  (limestone from shells), chert, coal
               Igneous Rocks
Properties of igneous rocks
• Igneous rocks are nonsedimentary in origin
• They form by solidification or crystallization
  of liquid rock under the Earth called magma
• Longer cooling time causes big crystals in the
  rock. Shorter cooling time causes small
  crystals in the rock.
• Texture of igneous rock depends on the size
  of the crystals.
               Igneous Rocks
Types of igneous rocks
Igneous rocks form a gradation between two
• Felsic rocks are high in Al and Si.
• Mafic rocks are high in Mg and Fe.
Generally, igneous rocks are identified on the
 basis of crystal size (texture) and mineral
               Igneous Rocks
Sequence of cooling of silicate minerals--
  Bowen’s Reaction Series
• Bowen’s reaction series accounts for the
  crystallization of intermediate and felsic
  magmas from an original basaltic (mafic)
  magma. It has two branches, continuous and
• In the continuous branch, calcium-rich
  plagioclase feldspar crystallizes first followed
  by sodium-rich plagioclase feldspar.
               Igneous Rocks
Sequence of cooling of silicate minerals--
  Bowen’s Reaction Series
• In the discontinuous branch there is a series
  of one mineral changing to another over time
  as the melt cools.
• The sequence is: olivine --> pyroxene -->
  amphibole --> biotite mica.
• At this point the two sequences finish with:
  potassium feldspar (orthoclase) --> muscovite
  mica --> quartz.
              Igneous Rocks
Importance of texture and composition
The texture of igneous rocks depends on the
 size of the crystals as well as their
 arrangement. Rocks with large crystals
 cooled slowly. Those with small crystals
 cooled faster.
Mafic rocks are denser and darker than felsic
 rocks (ex: pyroxene, olivine). Felsic rocks are
 lighter in color and denser (ex: quartz,
 felspar, mica)
           Metamorphic Rocks
Properties of metamorphic rocks
• Metamorphic rocks are also nonsedimentary
  in origin.
• Metamorphism is a response to heat and
  pressure within the Earth’s crust.
• Such conditions result from plate collisions,
  mountain building and sometimes localized
  heating such as with volcanic eruptions.
           Metamorphic Rocks
Properties of metamorphic rocks
• Metamorphic rocks form from
  recrystallization of pre-existing rocks.
• Metamorphic rocks often show banding
  where like crystals are arranged in layers.
• They have a distorted structure caused by
  curving and folding of the bands.
           Metamorphic Rocks
Foliated vs nonfoliated metamorphic rocks
• Foliated rocks have crystals arranged in
  parallel planes. Examples are slate, schist,
• Nonfoliated rocks do not have a preferred
  orientation among their minerals. Examples
  are marble, quartzite, greenstone.
          Metamorphic Rocks
Steps leading to the formation of gneiss
• Most gneiss begins with recrystallization of
  clay-rich sedimentary rocks during regional
• Gneisses are composed mainly of quartz
  and/or feldspar, which cause the light bands.
• The dark bands come from biotite and
          Metamorphic Rocks
Origin and composition of marble
Marble is a metamorphic rock that was
 originally limestone or dolomite. Limestone
 marble is made of CaCO3. Dolomite marble
 is made of CaMg(CO3)2.
Limestone marble reacts with the acid test.
  Dolomitic marble also reacts with the acid
  test but it must be powered first.
          Metamorphic Rocks
Regional metamorphism
• Regional metamorphism occurs over a wide
  area and results from tremendous
  temperatures, pressures and deformation
  conditions deep under the surface.
• It results in a gradation from from low to
  high metamorphism depending on the levels
  of temperature and pressure involved.
  Civilization and Earth Materials
Humans use fossil fuels for the major part of
 their energy needs. These include coal, oil
 and natural gas.
Minerals are used in a variety of human
Rocks are quarried and used as building stones
 and pavement.
Earth resources are not renewable. They
 cannot be restored easily in your lifetime.
        Landscape development
Landscapes are the features of the surface of
 the Earth.
Features include:
• slope of the land
• shape of surface features
• stream drainage patterns
• stream slope
• soil characteristics
        Landscape development
Measuring Landscape Characteristics
• Measurements can be made using actual
  observations, maps, aerial photographs or
  satellite images.
• Gradients, slopes and profiles are given on
  topological maps.
• Major types are mountains, plateaus and
        Landscape development
Forces that produce landscapes
• Uplift is a raising up of a region of land
  caused by forces in the crust or by tectonic
• Leveling forces break down rocks and
  transport material on the Earth’s surface.
  These include weathering, erosion,
  deposition, subsidence.
        Landscape development
Forces that produce landscapes
• Erosion is the removal of weathered rock
  materials from their source area.
• Mass wasting is the downslope movement of
  rocks, sediments, or soil under the influence
  of gravity.
        Landscape development
Factors that influence landscape development
• Climate affects the rate of change of a
• Glaciers produce U-shaped valleys and deposit
  soil with a wide range of particle sizes.
• Streams may not flow all the time in arid
  climates. Some arid regions have internal
  drainage where streams deposit water into a
  basin rather than leading to the ocean. The
  Great Salt Lake is an example.
        Landscape development
U-shaped valley caused by a glacier
        Landscape development
Factors that influence landscape development
• Bedrock greatly influences the landscape above
• Different types of rock have different degrees of
  resistance to weathering and erosion.
• Stream drainage patterns indicate information
  regarding the contour of the bedrock below.
        Landscape development
Human influence on landscape development
• Removal of forests for development leads to
  accelerated erosion of soil when it rains.
• Acid rain causes increased chemical weathering
  of rocks. Example: accelerated erosion of
• Environmental conservation can help conserve
  limited natural resources.
        Landscape development
Geologic features can be represented by
 photographs, as well as topographic and
 geological maps.
Maps are interpreted using scales and colors to
 represent features.
Topographic maps indicate locations of equal
 altitude using contour lines.
Geologic maps use colors and symbols to
 represent rock ages and structures.
        Landscape development
On a topographic map, the steepness of a slope is
 indicated by the nearness of the contour lines.
A very steep slope has contour lines very close
A long, gradual slope has contour lines far apart.
Direction on a contour map is indicated by an
 arrow pointing north. Distances are given by a
 distance scale.
              Natural Hazards
People live in risky places.
A flood plain can fill up with water and carry
 away the work of generations.
Seismic hazards are issues near faults, such as the
  San Andreas Fault.
It is not a good idea to live on the slopes of a
  volcano, lest it erupt. People live near Mt.
  Etna, anyhow.
    The End
3: Earth Materials and
   Surface Processes

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