Transcript Minerals of the Earth`s crust

Minerals, Rocks, and the Fossil Record
SES1. Students will investigate the composition and formation of Earth systems, including the
Earth’s relationship to the solar system.
c. Describe how the decay of radioactive isotopes is used to determine the age of rocks, Earth,
and solar system.
e. Identify the transformations and major reservoirs that make up the rock cycle, hydrologic
cycle, carbon cycle, and other important geochemical cycles.
SES2. Students will understand how plate tectonics creates certain geologic features, materials,
and hazards.
d. Associate specific plate tectonic settings with the production of particular groups of igneous
and metamorphic rocks and mineral resources.
SES4. Students will understand how rock relationships and fossils are used to reconstruct the
Earth’s past.
a. Describe and apply principles of relative age (superposition, original horizontality, crosscutting relations, and original lateral continuity) and describe how unconformities form.
b. Interpret the geologic history of a succession of rocks and unconformities.
c. Apply the principle of uniformitarianism to relate sedimentary rock associations and their
fossils to the environments in which the rocks were deposited.
d. Explain how sedimentary rock units are correlated within and across regions by a variety of
methods (e.g., geologic map relationships, the principle of fossil succession, radiometric
dating, and paleomagnetism).
e. Use geologic maps and stratigraphic relationships to interpret major events in Earth history
(e.g., mass extinction, major climatic change, tectonic events).
SES6. Students will explain how life on Earth responds to and shapes Earth systems.
d. Describe how fossils provide a record of shared ancestry, evolution, and extinction that is
best explained by the mechanism of natural selection.
Chapter 5
Chapter 5
Minerals of Earth’s Crust
SES2d. Associate specific plate tectonic settings
with the production of particular groups of
igneous and metamorphic rocks and mineral
resources
SES3d. Explain the processes that transport and
deposit material in terrestrial and marine
sedimentary basins, which result, over time, in
sedimentary rock.
Chapter 5
Section 1 What Is a Mineral?
To be a mineral, a substance must have
four characteristics:
 it must be inorganic—it cannot be made
of or by living things;
 it must occur naturally—it cannot be
man-made;
 it must be a crystalline solid;
 it must have a consistent chemical
composition.
Chapter 5
Section 1 What Is a Mineral?
 The 20 most common minerals are called rockforming minerals because they form the rocks
that make up Earth’s crust.
 Ten minerals are so common that they make up 90%
of Earth’s crust.
 These minerals are quartz, orthoclase, plagioclase,
muscovite, biotite, calcite, dolomite, halite, gypsum,
and ferromagnesian minerals.
 All minerals can be classified into two main
groups—silicate minerals and nonsilicate
minerals—based on their chemical
compositions.
Chapter 5
Section 1 What Is a Mineral?
Silicate Minerals
 silicate mineral a mineral that contains a combination
of silicon and oxygen, and that may also contain one or
more metals
 Common silicate minerals include quartz, feldspars,
micas ,and ferromagnesian minerals, such as
amphiboles, pyroxenes, and olivines.
 Silicate minerals make up 96% of Earth’s crust. Quartz
and feldspar alone make up more than 50% of the
crust.
Chapter 5
Section 1 What Is a Mineral?
Nonsilicate Minerals
 nonsilicate mineral a mineral that does not contain
compounds of silicon and oxygen
 Nonsilicate minerals comprise about 4% of Earth’s
crust.
 Nonsilicate minerals are organized into six major
groups based on their chemical compositions.
 The six major groups of nonsilicate minerals are
carbonates, halides, native elements, oxides, sulfates,
and sulfides.
Chapter 5
Section 1 What Is a Mineral?
 Each type of mineral is characterized by a
specific geometric arrangement of atoms, or its
crystalline structure.
 crystal a solid whose atoms, ions, or molecules
are arranged in a regular, repeating pattern
 One way that scientists study the structure of
crystals is by using X rays. X rays that pass
through a crystal and strike a photographic
plate produce an image that shows the
geometric arrangement of the atoms in the
crystal.
Chapter 5
Section 1 What Is a Mineral?
 Even though there are many kinds of silicate minerals, their
crystalline structure is made up of the same basic building
blocks—silicon-oxygen tetrahedra.
 silicon-oxygen tetrahedron the basic unit of the structure of
silicate minerals; a silicon ion chemically bonded to and
surrounded by four oxygen ions
Isolated Tetrahedral Silicates
 In minerals that have isolated tetrahedra, only atoms other
than silicon and oxygen atoms like silicon-oxygen tetrahedra
together.
 Olivine is an isolated tetrahedral silicate.
Chapter 5
Section 1 What Is a Mineral?
The diagram below shows the tetrahedral arrangement of isolated
tetrahedral silicate minerals.
Chapter 5
Section 1 What Is a Mineral?
Ring Silicates
 Ring silicates form when shared oxygen atoms join the tetrahedra
to form three-, four-, or six-sided rings.
 Beryl and tourmaline are ring silicates.
Single-Chain Silicates
 In single-chain silicates, each tetrahedron is bonded to two others
by shared oxygen atoms.
 Most double-chain silicates are called pyroxenes.
Chapter 5
Section 1 What Is a Mineral?
The diagram below shows the tetrahedral arrangement of ring silicate
minerals.
Chapter 5
Section 1 What Is a Mineral?
The diagram below shows the tetrahedral arrangement of single-chain
silicate minerals.
Chapter 5
Section 1 What Is a Mineral?
Double-Chain Silicates
 In double-chain silicates, two single chains of tetrahedra
bond to each other.
 Most double-chain silicates are called amphiboles.
Sheet Silicates
 In the sheet silicates, each tetrahedron shares three
oxygen atoms with other tetrahedra. The fourth oxygen
atom bonds with an atom of aluminum or magnesium,
which joins the sheets together.
 The mica minerals, such as muscovite and biotite, are
sheet silicates.
Chapter 5
Section 1 What Is a Mineral?
The diagram below shows the tetrahedral arrangement of doublechain silicate minerals.
Chapter 5
Section 1 What Is a Mineral?
The diagram below shows the tetrahedral arrangement of sheet
silicate minerals.
Chapter 5
Section 1 What Is a Mineral?
Framework Silicates
 In the framework silicates, each tetrahedron is bonded
to four neighboring tetrahedra to form a threedimensional network.
 Frameworks that contain only silicon-oxygen
tetrahedra are the mineral quartz.
 Other framework silicates contain some tetrahedra in
which atoms of aluminum or other metals substitute
for some of the silicon atoms.
 Quartz and feldspars are framework silicates.
Chapter 5
Section 1 What Is a Mineral?
The diagram below shows the tetrahedral arrangement of framework
silicate minerals.
Chapter 5
Section 1 What Is a Mineral?
 Because nonsilicate minerals have diverse chemical
compositions, nonsilicate minerals display a vast variety of
crystalline structures.
 Common crystalline structures for nonsilicate minerals
include cubes, hexagonal prisms, and irregular masses.
 The structure of a nonsilicate crystal determines the
mineral’s characteristics.
 In the crystal structure called closest packing, each metal atom
is surrounded by 8 to 12 other metal atoms that are as close
to each other as the charges of the atomic nuclei will allow.
Chapter 5
Section 2 Identifying Minerals
Color
 While color is a property that is easily observed, it is
unreliable for the identification of minerals.
 The color of a mineral sample can be affected by the
inclusion of impurities or by weathering processes.
Streak
 streak the color of a mineral in powdered form
 Streak is more reliable than color for the identification of
minerals.
 Streak is determined by rubbing some of the mineral
against an unglazed ceramic tile called a streak plate.
Chapter 5
Section 2 Identifying Minerals
Luster
 luster the way in which a mineral reflects light
 A mineral is said to have a metallic luster if the mineral
reflects light as a polished metal does.
 All other minerals have nonmetallic luster.
 There are several types of nonmetallic luster, including
glassy, waxy, pearly, brilliant, and earthy.
Chapter 5
Section 2 Identifying Minerals
Cleavage and Fracture
 cleavage in geology, the tendency of a mineral to split
along specific planes of weakness to form smooth, flat
surfaces
 fracture the manner in which a mineral breaks along either
curved or irregular surfaces
 Uneven or irregular fractures have rough surfaces.
 Splintery or fibrous fractures look like a piece of broken
wood.
 Curved surfaces are conchoidal fractures .
Chapter 5
Section 2 Identifying Minerals
Hardness
 The measure of the ability of a mineral to resist scratching is
called hardness. Hardness does not mean “resistance to
cleavage or fracture.”
 The hardness of a mineral can be determined by comparing
the mineral to minerals of Mohs hardness scale.
 Mohs hardness scale the standard scale against which the
hardness of minerals is rated.
 The strength of the bonds between the atoms that make up
a mineral’s internal structure determines the hardness of a
mineral.
Chapter 5
Section 2 Identifying Minerals
The diagram below shows Mohs Hardness Scale.
Chapter 5
Section 2 Identifying Minerals
Density
 density the ratio of the mass of a substance to
the volume of a substance; commonly
expressed as grams per cubic centimeter for
solids
 The density of a mineral depends on the kinds
of atoms in the mineral and on how closely the
atoms are packed.
density = mass  volume
Chapter 5
Section 2 Identifying Minerals
 A few minerals have some additional, special
properties that can help identify those minerals.
Fluorescence and Phosphorescence
 The ability to glow under ultraviolet light is called
fluorescence.
 Fluorescent minerals absorb ultraviolet light and then
produce visible light of various colors.
 The property of some minerals to glow after the
ultraviolet light is turned off is called phosphorescence.
Chapter 5
Section 2 Identifying Minerals
Chatoyancy and Asterism
 In reflected light, some minerals display a silky appearance
that is called chatoyancy, or the cat’s-eye effect.
 A similar effect called asterism is the phenomenon in which a
six-sided star appears when a mineral reflects light.
Double Refraction
 The property of some minerals, particularly some forms of
calcite, to produce a double image of any object viewed
through the mineral is called double refraction.
Chapter 5
Section 2 Identifying Minerals
Magnetism
 Minerals that are attracted to magnets display the
property of magnetism. These minerals may be magnetic
themselves.
 In general, nonsilicate minerals that contain iron are
more likely to be magnetic than silicate minerals are.
Radioactivity
 The property known as radioactivity results as unstable
nuclei decay over time into stable nuclei by releasing
particles and energy.
 A Geiger counter is used to detect the released particles
and, thus, to identify minerals that are radioactive.
Chapter 6
Chapter 6


SES2d. Associate specific plate tectonic
settings with the production of particular
groups of igneous and metamorphic rocks
and mineral resources
SES3e. Explain the processes that transport
and deposit material in terrestrial and
marine sedimentary basins, which result,
over time, in sedimentary rock.
The material that makes up the solid
parts of Earth is known as rock.
Made of a mixture of minerals and
organic material.
Based on the processes that form and
change the rocks of Earth’s crust,
geologists classify rocks into three
major types by the way the rocks
form.
 All rock has physical and chemical
properties that are determined by how and
where the rock formed.
 The rate at which rock weathers and the
way that rock breaks apart are determined
by the chemical stability of the minerals in
the rock.
 The rate at which mineral chemically breaks down is
dependent on the chemical stability of the mineral.
 Rocks have natural zones of weakness that are
determined by how and where the rocks form.
 Igneous rock forms when magma, or molten
rock, cools and hardens.
 Sedimentary rock forms when sediment
deposits that form when rocks, mineral
crystals, and organic matter have been broken
into fragments, called sediments, are
compressed or cemented together.
 Metamorphic rock forms when existing rock
is altered by changes in temperature, by
changes in pressure, or by chemical
processes.
 Any of the three major types of rock can be
changed into another of the three types.
 Geologic forces and processes cause rock
to change from one type to another.
 rock cycle the series of processes in which
rock forms, changes from one form to
another, is destroyed, and forms again by
geological processes
 Igneous rocks are classified according to where magma
cools and hardens.
 intrusive igneous rock rock formed from the cooling
and solidification of magma beneath Earth’s surface
 extrusive igneous rock rock formed from the cooling
and solidification of lava at Earth’s surface
 The texture of igneous rock is determined by the size of
the crystals in the rock. The size of the crystals in
determined mainly by the cooling rate of the magma.
Coarse-Grained Igneous Rock
 Because intrusive igneous rocks cool slowly, they commonly have
large mineral crystals.
 Igneous rocks that are composed of large, well-developed mineral
grains are described as having a coarse-grained texture.
Fine-Grained Igneous Rock
 Because extrusive igneous rocks cool rapidly, they are commonly
composed of small mineral grains.
 Igneous rocks that are composed of small crystals are described as
having a fine-grained texture.

Pumice rocks are igneous
rocks which were formed
when lava cooled quickly
above ground. You can see
where little pockets of air
had been. This rock is so
light, that many pumice
rocks will actually float in
water. Pumice is actually a
kind of glass and not a
mixture of minerals.
Because this rock is so
light, it is used quite often
as a decorative landscape
stone. Ground to a powder,
it is used as an abrasive in
polish compounds and in
Lava© soap.

Granite rocks are
igneous rocks which
were formed by
slowly cooling
pockets of magma
that were trapped
beneath the earth's
surface. Granite is
used for long lasting
monuments and for
trim and decoration
on buildings.

Scoria rocks are
igneous rocks which
were formed when
lava cooled quickly
above ground. You
can see where little
pockets of air had
been. Scoria is
actually a kind of
glass and not a
mixture of minerals.

Obsidian rocks are
igneous rocks that
form when lava cools
quickly above
ground. Obsidian is
actually glass and not
a mixture of minerals.
The edges of this
rock are very sharp.
 Most sedimentary rock is made up of combinations of
different types of sediment, which is loose fragments
of rock, minerals, and organic materials.
 Two main processes convert loose sediment into
sedimentary rock—compaction and cementation.
 compaction the process in which the volume and
porosity of a sediment is decreased by the weight of
overlying sediments as a result of burial beneath other
sediments
 cementation the process in which minerals precipitate
into pore spaces between sediment grains and bind
sediments together to form rock
 Geologists classify sedimentary rocks by the
processes by which the rocks form and by the
composition of the rocks.
 There are three main classes of sedimentary
rocks—chemical, organic, and clastic.
 These three classes contain their own
classifications of rocks that are grouped based
on the shape, size, and composition of the
sediments that form the rocks.
 chemical sedimentary rock sedimentary rock that forms
when minerals precipitate from a solution or settle from
a suspension
 Some chemical sedimentary rock forms when dissolved
minerals precipitate out of water because of changing
concentrations of chemicals.
 When water evaporates, the minerals that were dissolved
in the water are left behind. Eventually, the concentration
of minerals in the remaining water becomes high enough
to cause minerals to precipitate out of the water.
 Rocks that form through evaporation are called
evaporites. Gypsum and halite are common evaporites.

Gypsum rocks are
sedimentary rocks
made up of sulfate
mineral and formed
as the result of
evaporating sea
water in massive
prehistoric basins.
It is very soft and is
used to make
Plaster of Paris,
casts, molds, and
wallboards.
 organic sedimentary rock sedimentary rock that forms
from the remains of plants or animals
 Coal and some limestones are examples of organic
rocks.
 Organic limestones form when marine organisms, such
as coral, clams, oysters, and plankton, remove the
chemical components of the minerals calcite and
aragonite from sea water.
 The organisms make their shells from these minerals,
and when the organisms die, their shells settle to the
bottom of the ocean, accumulate, and are compacted to
form limestone.
Chapter 6
Section 3 Sedimentary Rock
The diagram below shows the formation of organic limestone.

Limestone rocks are
sedimentary rocks that
are made from the
mineral calcite which
came from the beds of
evaporated seas and
lakes and from sea
animal shells. This rock
is used in concrete and
is an excellent building
stone for humid
regions.
 clastic sedimentary rock sedimentary rock that forms
when fragments of preexisting rocks are compacted or
cemented together
 Clastic sedimentary rocks are classified by the size of the
sediments they contain.
 Rock that contains large, rounded pieces is called
conglomerate. Rock that contains large, angular pieces is
called breccia.
 Rock that is composed of sand-sized grains is called
sandstone. Rock that is composed of clay-sized particles is
called shale.
 The physical characteristics of sediments are
determined mainly by the way sediments were
transported to the place where they are deposited.
 Sediments are transported by four main agents: water,
ice, wind, and the effects of gravity.

Conglomerate rocks
are sedimentary rocks.
They are made up of
large sediments like
sand and pebbles.
The sediment is so
large that pressure
alone cannot hold the
rock together; it is also
cemented together
with dissolved
minerals.

Sandstone rocks
are sedimentary
rocks made from
small grains of the
minerals quartz
and feldspar. They
often form in layers
as seen in this
picture. They are
often used as
building stones.

Shale rock is a
type of
sedimentary rock
formed from clay
that is compacted
together by
pressure. They are
used to make
bricks and other
material that is
fired in a kiln.
 metamorphism the process in which one type of rock
changes into metamorphic rock because of chemical
processes or changes in temperature and pressure
 During metamorphism, heat, pressure, and hot fluids
cause some minerals to change into other minerals.
 Minerals may also change in size or shape, or they may
separate into parallel bands that give the rock a layered
appearance.
 Hot fluids may circulate through the rock and change the
mineral composition of the rock by dissolving some
materials and by adding others.
 The type of rock that forms because of metamorphism
can indicate the conditions under which the original
rock changed.
 The composition of the rock being metamorphosed, the
amount and direction of pressure, and the presence or
absence of certain fluids cause different combinations
of minerals to form.
 Two types of metamorphism occur in Earth’s crust—
contact metamorphism and regional metamorphism.
Contact Metamorphism
 contact metamorphism a change in the texture,
structure, or chemical composition of a rock due to
contact with magma
Regional Metamorphism
 regional metamorphism a change in the texture,
structure, or chemical composition of a rock due to
changes in temperature and pressure over a large area,
generally are a result of tectonic forces
Foliated Rocks
 foliation the metamorphic rock texture in which
minerals grains are arranged in planes or bands
 Extreme pressure may cause the mineral crystals in the
rock to realign or regrow to form parallel bands.
 Foliation also occurs as minerals that have different
compositions separate to produce a series of
alternating dark and light bands.
 Foliated metamorphic rocks include the common rocks
slate, schist, and gneiss.

Gneiss rocks are
metamorphic. These
rocks may have been
granite, which is an
igneous rock, but heat
and pressure changed it.
You can see how the
mineral grains in the rock
were flattened through
tremendous heat and
pressure and are
arranged in alternating
patterns.

Schist rocks are
metamorphic. These
rocks can be formed
from basalt, an
igneous rock; shale, a
sedimentary rock; or
slate, a metamorphic
rock. Through
tremendous heat and
pressure, these rocks
were transformed into
this new kind of rock.
Nonfoliated Rocks
 nonfoliated the metamorphic rock texture in which minerals
grains are not arranged in planes or bands
 Many nonfoliated metamorphic rocks contain grains of only one
mineral or contain very small amounts of other minerals. Thus,
the rock does not form bands of different minerals.
 Other nonfoliated metamorphic rocks contain grains that are
round or square. These grains are unlikely to change shape or
position when exposed to directed pressure.
 Nonfoliated metamorphic rocks include the common rocks
marble and quartzite.
 The three factors that affect whether rock
melts include temperature, pressure, and
the presence of fluids in the rock.
Chapter 8
SES1. Students will investigate the composition and formation of Earth systems,
including the Earth’s relationship to the solar system.
c. Describe how the decay of radioactive isotopes is used to determine the age of rocks,
Earth, and solar system.
SES4. Students will understand how rock relationships and fossils are used to reconstruct
the Earth’s past.
a. Describe and apply principles of relative age (superposition, original horizontality,
cross-cutting relations, and original lateral continuity) and describe how unconformities
form.
b. Interpret the geologic history of a succession of rocks and unconformities.
c. Apply the principle of uniformitarianism to relate sedimentary rock associations and
their fossils to the environments in which the rocks were deposited.
d. Explain how sedimentary rock units are correlated within and across regions by a
variety of methods (e.g., geologic map relationships, the principle of fossil succession,
radiometric dating, and paleomagnetism).
e. Use geologic maps and stratigraphic relationships to interpret major events in Earth
history (e.g., mass extinction, major climatic change, tectonic events).
SES6. Students will explain how life on Earth responds to and shapes Earth systems.
d. Describe how fossils provide a record of shared ancestry, evolution, and extinction
that is best explained by the mechanism of natural selection.
uniformitarianism a principle that geologic processes
that occurred in the past can be explained by
current geologic processes
 Geologists estimate that Earth is about 4.6 billion
years old, an idea that was first proposed by James
Hutton in the 18th century.
 Hutton theorized that the same forces that change
Earth’s surface now, such as volcanism and
erosion, are the same forces that were at work in
the past.
relative age the age of an object in relation to the
ages of other objects
 One way to learn about Earth’s past is to
determine the order in which rock layers and other
rock structures formed.
 Layers of rock, called strata, show the sequence of
events that took place in the past.
 Once they know the order, a relative age can be
determined for each layer.
 Relative age indicated that one layer is older or
younger than another layer but does not indicate
the rock’s age in years.
law of superposition the law that a sedimentary rock layer is
older than the layers above it and younger than the layers
below it if the layers are not disturbed
 Scientists commonly study the layers in sedimentary rocks
to determine the relative age of rocks.
 Sedimentary rocks form when new sediments are deposited
on top of old layers of sediment.
 As the sediments accumulate, they harden into layers called
beds. The boundary between two beds is called a bedding
plane.
 Scientists use a basic principle called the law of
superposition to determine the relative age of a layer of
sedimentary rock.
The diagram below illustrates the law of Superposition.
 Scientist know that sedimentary rock generally
forms in horizontal layers.
 The principle of original horizontality states that
sedimentary rocks left undisturbed will remain
in horizontal layers.
 So, scientists can assume that sedimentary rock
layers that are not horizontal have been tilted
or deformed by crustal movements that
happened after the layers formed.
unconformity
a break in
the geologic
record
created
when rock
layers are
eroded or
when
sediment is
not
deposited
for a long
period of
time.
law of crosscutting relationships the principle that a fault or
body of rock is younger than any other body of rock that it
cuts through.
absolute age the numeric age of an object or
event, often stated in years before the present,
as established by an absolute-dating process,
such as radiometric dating
 Scientists use a variety of ways to determine
absolute age, or the numeric age, of a rock
formation.
Rates of Erosion
 One way scientists use to estimate absolute age
is to study rates of erosion.
 Studying the rates of erosion is practical only
for geologic features that formed within the
past 10,000 to 20,000 years.
 For older surface features, the method is less
dependable because rates of erosion can vary
over millions of years.
Rates of Deposition
 Scientists can also estimate absolute age by
calculating the rate of sediment deposition.
 By using data collected over a long period of time,
geologists can estimate the average rates of
deposition for common sedimentary rocks.
 This method is not always accurate because not all
sediment is deposited at an average; therefore it
provides only an estimate of absolute age.
Varve Count
varve a banded layer of sand and silt that is
deposited annually in a lake, especially near ice
sheets or glaciers, and that can be used to
determine absolute age.
 Some sedimentary deposits show definite annual
layers, called varves.
 The varves can be counted much like tree rings to
determine the age of the sedimentary deposit.
radiometric dating a method of determining the
absolutes age of an object by comparing the
relative percentages of a radioactive (parent)
isotope and a stable (daughter) isotope.
 Rocks generally contain small amounts of
radioactive material that can act as natural
clocks.
 Atoms of the same element that have different
numbers of neutrons are called isotopes.
 Radioactive isotopes can be used to determine age.
 Radioactive isotopes have nuclei that emit
particles and energy at a constant rate
regardless of surrounding conditions.
 Scientists use the natural breakdown of isotopes
to accurately measure the absolute age of rock,
which is called radiometric dating.
 To do this, scientists measure the concentration
of the parent isotope or original isotope, and of
the newly formed daughter isotopes. Then, using
the known decay rate, they can determine the
absolute age of the rock.
half-life the time required for half of a sample of a
radioactive isotope to break down by radioactive
decay to form a daughter isotope.
 Scientists have determined that the time required
for half of any amount of a particular radioactive
isotope to decay is always the same and can be
determined for any isotope.
 By comparing the amounts of parent and daughter
isotopes in a rock sample, scientists can determine
the age of the sample.
 The greater the percentage of daughter isotopes
present in the sample, the older the rock is.
Radioactive Isotopes
 Uranium-238, or 238U, is an isotope of uranium that
has an extremely long half-life, and is most useful
for dating geologic samples that are more than 10
million years old.
 Potassium-40, or 40K, has a half-life of 1.25 billion
years, and is used to date rock that are between
50,000 and 4.6 billion years old.
 Rubidium-87 has a half-life of about 49 billion
years, and is used to verify the age of rocks
previously dated by using 40K.
Carbon Dating
 Younger rock layers may be dated indirectly by dating
organic material found within the rock.
 Organic remains, such as wood, bones, and shells that are
less than 70,000 years old can be determined by using a
method known as carbon-14 dating, or radiocarbon dating.
 All living organisms have both the carbon-12 and carbon14 isotope.
 To find the age of a sample of organic material, scientists
compare the ratio of 14C to 12C and then compare this with
the ratio of 14C to 12 C known to exist in a living organism.
 Once a plant or animal dies, the ratio begins to change,
and scientist can determine the age from the difference
between the ratios of 14C to 12C in the dead organism.
fossils the trace or remains of an organism that
lived long ago, most commonly preserved in
sedimentary rock
paleontology the scientific study of fossils
 Fossils are an important source of information
for finding the relative and absolute ages of
rocks.
 Fossils also provide clues to past geologic
events, climates, and the evolution of living
things over time.
 Almost all fossils are discovered in
sedimentary rock.
 The fossil record provides information about
the geologic history of Earth.
 Scientists can use this information to learn
about how environmental changes have
affected living organisms.
 Only dead organisms that are buried quickly or
protected from decay can become fossils.
 Generally only the hard parts of organisms,
such as wood, bones, shells, and teeth, become
fossils.
 In rare cases, an entire organism may be
preserved.
 In some types of fossils, only a replica of the
original organism remains. Others merely
provide evidence that life once existed.
Mummification
 Mummified remains are often found in very
dry places, because most bacteria which cause
decay cannot survive in these places.
 Some ancient civilizations mummified their
daed by carefully extracting the body’s internal
organs and then wrapping the body in
carefully prepared strips of cloth.
Amber
 Hardened tree sap is called amber. Insects
become trapped in the sticky sap and are
preserved when the sap hardens.
 In many cases, delicate features such as legs
and antennae have been preserved. In rare
cases, DNA has been recovered from amber.
Tar Seeps
 When thick petroleum oozes to Earth’s surface,
the petroleum forms a tar seep.
 Tar seeps are commonly covered by water.
Animals that come to drink the water can
become trapped in the sticky tar.
 The remains of the trapped animals are
covered by the tar and preserved.
Freezing
 The low temperatures of frozen soil and ice can
protect and preserve organisms.
 Because most bacteria cannot survive freezing
temperatures, organisms that are buried in
frozen soil or ice do not decay.
Petrification
 Mineral solutions such as groundwater replace
the original organic materials that were
covered by layers of sediment with new
materials.
 Some common petrifying minerals are silica,
calcite, and pyrite.
 The substitution of minerals for organic
material other results in the formation of a
nearly perfect mineral replica of the original
organism.
trace fossil a fossilized mark that formed in
sedimentary rock by the movement of an
animal on or within soft sediment
 In some cases, no part of the original organism
survives in fossil form. But the fossilized
evidence of past animal movement can still
provide information about prehistoric life.
 A trace fossils in an important clue to the
animal’s appearance and activities.
Imprints
 Carbonized imprints of leaves, stems, flowers,
and fish made in soft mud or clay have been
found preserved in sedimentary rock.
 When original organic material partially
decays, it leaves behind a carbon-rich film. An
imprint displays the surface features of the
organism.
Molds and Casts
 Shells often leave empty cavities called molds
within hardened sediment. When a shell is
buried, its remains eventually decay and leave
an empty space.
 When sand or mud fills a mold and hardens, a
natural cast forms.
 A cast is a replica of the original organism.
Coprolites
 Fossilized dung or waste materials from
ancient animals are called coprolites.
 They can be cut into thin sections and observed
through a microscope. The materials identified
in these sections reveal the feeding habits of
ancient animals, such as dinosaurs.
Gastroliths
 Some dinosaurs had stones in their digestive
systems to help grind their food. In many cases,
these stones, which are called gastroliths,
survives as fossils.
 Gastroliths can often be recognized by their
smooth, polished surfaces and by their close
proximity to dinosaurs remains.
Index fossils
 Index fossil a fossil that is used to establish the age of
rock layers because it is distinct, abundant, and
widespread and existed for only a short span of geologic
time.
 Paleontologists can use index fossils to determine the
relative ages of the rock layers in which the fossils are
located.
 To be an index fossil, a fossil must be present in rocks
scattered over a large region, and it must have features
that clearly distinguish it from other fossils.
 In addition, organisms from which the fossil formed
must have lived during a short span of geologic time, and
the fossil must occur in fairly large numbers within the
rock layers.
 Scientists can use index fossils to estimate absolute ages of specific
rock layers.
Because organisms that
formed index fossils lived
during short spans of
geologic time, the rock layer
in which an index fossil was
discovered can be dated
accurately.
Scientists can also use index
fossils to date rock layers in
separate area.
Index fossils are used to
help locate rock layers that
are likely to contain oil and
natural gas deposits.
Chapter 9
SES4. Students will understand how rock relationships and fossils are used to
reconstruct the Earth’s past.
a. Describe and apply principles of relative age (superposition, original
horizontality, cross-cutting relations, and original lateral continuity) and
describe how unconformities form.
b. Interpret the geologic history of a succession of rocks and unconformities.
c. Apply the principle of uniformitarianism to relate sedimentary rock
associations and their fossils to the environments in which the rocks were
deposited.
d. Explain how sedimentary rock units are correlated within and across
regions by a variety of methods (e.g., geologic map relationships, the principle
of fossil succession, radiometric dating, and paleomagnetism).
e. Use geologic maps and stratigraphic relationships to interpret major events
in Earth history (e.g., mass extinction, major climatic change, tectonic events).
SES6. Students will explain how life on Earth responds to and shapes Earth
systems.
d. Describe how fossils provide a record of shared ancestry, evolution, and
extinction that is best explained by the mechanism of natural selection.
geologic column an ordered arrangement of rock layers that is based on
the relative ages of the rocks and in which the oldest rocks are at the
bottom.
 Evidence of changing conditions on Earth’s surface is recorded in the
rock layers of Earth’s crust.
 The geologic time scale outlines the development of Earth and of life
on Earth.
 No single area on Earth contained a record of all geologic time, so
scientists combined observations to create a standard geologic
column.
 Rock layers in a geologic column are distinguished by the types of
rock the layers are made of and by the kinds of fossils the layers
contain.
 Fossils in the upper layers resemble modern plants and animals.
 Many of the fossils discovered in old layers are from species that have
been extinct for millions of years.
 The geologic history of Earth is marked by
major changes in Earth’s surface, climate, and
types of organisms.
 Geologists use these indicators to divide the
geologic time scale into smaller units.
 Rocks grouped within each unit contain similar
fossils and each unit is generally characterized
by fossils of a dominant life-form.
Eons
 The largest unit of geologic unit of time is an
eon. Geologic time is divided into four eons:
the Hadean eon, the Archean eon, the
Proterozoic eon, and the Phanerozoic eon.
 The first three eons are part of a time interval
commonly known as Precambrian Time. This 4
billion year interval contains most of Earth’s
history.
Eras
era a unit of geologic time that includes two or more periods
 After Precambrian time the Phanerozoic eon began. This eon
is divided into smaller units of geologic time called eras.
 The first era of the Phanerozoic eon was the Paleozoic Era,
which lasted 292 million years.
 Paleozoic rocks contain fossils of a wide variety of marine
and terrestrial life forms.
 After the Paleozoic Era the Mesozoic Era began and lasted
about 183 million years.
 Mesozoic fossils include early forms of birds and reptiles.
 The present era is the Cenozoic Era, which began 65 million
years ago. Fossils of mammals are common in Cenozoic
rocks.
Periods and Epochs
 Eras are divided into shorter time units called periods. Each period is
characterized by specific fossils and is usually named for the location
in which the fossils were first discovered.
period a unit of geologic time that is longer than an epoch but shorter
than an era
 Where the rock record is most complete and least deformed, a
detailed fossil record may allow scientists to divide period into
shorter time units called epochs.
epoch a subdivision of geologic time that is longer than an age but
shorter than a period.
 Epochs may be divided into smaller units of time called ages.
 Ages are defined by the occurrence of distinct fossils in the fossil
record.
evolution an inheritable change in the
characteristics within a population from one
generation to the next; the development of new
types of organisms from preexisting types of
organisms over time
 By examining rock layers and fossils, scientists
have discovered evidence that species of
livings things have changed over time.
 Scientists call this process evolution.
Evolution and Geologic Change
 Scientists think that evolution occurs by
means of natural selection. Evidence for
evolution included the similarity in skeletal
structures of animals.
 Major geologic and climatic changes can
affect the ability of some organisms to
survive.
 By using geologic evidence, scientists try to
determine how environmental changes
affected organisms in the past.
Precambrian time the interval of time in the
geologic time scale from Earth’s formation
to the beginning of the Paleozoic era, from
4.6 billion to 542 million years ago.
 The time interval that began with the
formation of Earth and ended about 542
million years ago is known as Precambrian
time, which makes up 88% of Earth’s
history.
 The Precambrian rock record is difficult to
interpret, therefore we do not know much
about what happened during that time.
 Most Precambrian rocks have been so severely
deformed and altered by tectonic activity that
the original order of rock layers is rarely
identifiable.
Precambrian Rocks
 Large areas of exposed Precambrian rocks,
called shields, exist on every continent.
 Nearly half of the valuable mineral deposits in
the world occur in the rocks of Precambrian
shields.
 These valuable minerals include nickel, iron,
gold, and copper.
Precambrian Life
 Fossils are rare in Precambrian rocks mostly
because Precambrian life-forms lacked bones,
or other hard parts that commonly form fossils.
 One of the few Precambrian fossils that have
been discovered are stromatolites.
 The presence of stromatolite fossils in
Precambrian rocks indicates that shallow seas
covered much of Earth during that time.
Paleozoic Era the geologic era that followed
Precambrian time and that lasted from 542
million to 251 million years ago.
 Paleozoic rocks hold an abundant fossil record.
The number of plant and animal species on
Earth increased dramatically at the beginning
of the Paleozoic Era.
 Because of this rich fossil record, the Paleozoic
Era has been divided into seven periods.
The Cambrian Period
 The Cambrian Period is the first period of the Paleozoic Era.
 Marine invertebrates thrived in the warm waters that existed
during this time.
 The most common of the Cambrian invertebrates were trilobites.
Scientists use many trilobites as index fossils to date rocks to the
Cambrian Period.
 The second most common animals of the Cambrian Period were
the brachiopods, a group of shelled animals.
 Fossils indicated that at least 15 different families of brachiopods
existed during this period.
 Other common Cambrian invertebrates include worms, jellyfish,
snails, and sponges.
The Ordovician Period
 During this period, populations of trilobites began to shrink, and
clamlike brachiopods and cephalopod mollusks became the
dominant invertebrate life-form.
 Colonies of graptolites also flourished in the oceans, and the first
vertebrates appeared.
 The most primitive vertebrates were fish, which did not have jaws
or teeth and were covered with thick, bony plates.
The Silurian Period
 During the Silurian Period, echinoderms,
relatives of modern sea stars, and corals
became more common.
 Scorpion-like sea creatures called eurypterids
also existed during this period.
 Near the end of this period, the earliest land
plants as well as animals evolved on land.
The Devonian Period
 The Devonian Period is called the Age of Fishes because fossils of
many bony fishes were discovered in rocks of this period.
 On type of fish, called a lungfish, had the ability to breathe air.
Another type of fish, Rhipidistians, were air-breathing fish that
had strong fins that may have allowed them to crawl onto the land
for short periods of time.
 Land plants, such as giant horsetails, ferns, and cone-bearing
plants also began to develop during this period.
The Carboniferous Period
 In North America, the Carbiniferous Period is
divided into the Mississippian and
Pennsylvanian Periods.
 During this time, the climate was warm, and
forests and swamps covered most of the world.
 Amphibians and fish continued to flourish, and
the first vertebrates that were adapted to live
on land appeared.
The Permian Period
 The Permian Period marks the end of the Paleozoic Era, because a
mass extinction of a several life-forms occurred at the end of this
period.
 During this time, the continents had joined to form Pangaea, and
as a result, the seas that covered the world retreated.
 As the seas retreated, several species of marine life became extinct.
But, reptiles and amphibians survived the environmental changes.
mass extinction an episode during which large
numbers of species become extinct
Mesozoic Era the geologic era that lasted from 251
million to 65.5 million years ago; also called the
Age of Reptiles.
 Earth’s surface changed dramatically during the
Mesozoic Era. Pangaea broke into smaller
continents, and the climate was warm and humid.
 Lizards, turtles, snakes and dinosaurs flourished
during this era.
The Triassic Period
 The Mesozoic Era is known as the Age of Reptiles and is divided
into three periods: the Triassic, the Jurassic, and the Cretaceous
Periods.
 The Triassic period marked the appearance of dinosaurs. Most
dinosaurs were about 4 m to 5 m long and moved very quickly.
 Reptiles called ichthyosaurs lived in the oceans. The ammonite, a
marine invertebrate, was dominant, and serves as a Mesozoic
index fossil.
The Jurassic Period
 Two major groups of dinosaurs evolved during
the Jurassic Period: the saurischians, or “lizardhipped” dinosaurs, and the ornithischians, or
“bird-hipped” dinosaurs.
 Brontosauruses, now called Apatosauruses
were saurischians. Stegosauruses and
Pterosaurs were ornithischians.
The Cretaceous Period
 Among the common Cretaceous dinosaurs were the
Tyrannosaurus Rex, the ankylosaurs, the ceratopsians, and the
hadrosaurs.
 The earliest flowering plants, or angiosperms, appeared during
this period. The most common of these plants were magnolias and
willows.
 Later, trees such as maples, oaks, and walnuts became abundant.
The Cretaceous-Tertiary Mass Extinction
 The Cretaceous Period ended in another mass extinction. No
dinosaur fossils have been found in rocks that formed after the
Cretaceous Period.
 Many scientists accept the impact hypothesis as the explanation
for the extinction of the dinosaurs. This hypothesis is that about 65
million years ago, a giant meteorite crashed into Earth.
 The impact of the collision raised enough dust to block the sun’s
rays for many years, resulting in a colder climate that caused plant
life to die and many animal species to become extinct.
Cenozoic Era the current geologic era, which began 65.5 million
years ago; also called the Age of Mammals
 During the Cenozoic Era, dramatic changes in climate have
occurred. As temperatures decreased during the ice ages, new
species that were adapted to life in cooler climates appeared.
 Mammals became the dominant life-form and underwent many
changes.
 The Cenozoic Era is divided into two periods: the Tertiary Period
and the Quaternary Period.
The Quaternary and Tertiary Periods
 The Tertiary Period includes the time before
the last ice age, and is divided into five epochs:
The Paleocene, Eocene, Oligocene, Miocene,
and Pliocene Epochs.
 The Quaternary Period began with the last ice
age and includes the present.
 The Quaternary is divided into two epochs:
The Pleistocene and Holocene Epochs.
The Paleocene and Eocene Epochs
 The fossil record indicates that during the
Paleocene Epoch many new mammals, such as
small rodents, evolved.
 Other mammals, including the earliest known
ancestor of the horse, first whales, flying
squirrels, and bats, evolved during this time.
 Worldwide, temperatures dropped by about
4ºC at the end of the Eocene Epoch.
The Oligocene and Miocene Epochs
 During these epochs, the worldwide climate
became significantly cooler and drier. The modern
Antarctic icecap began to form. The Mediterranean
Sea dried up and refilled several times.
 This climate change caused many early mammals
to become extinct. However large species of deer,
pigs, horses, camels, cats, and dogs flourished.
Also, the climate change favored grasses, conebearing, and hardwood trees.
The Pliocene Epoch
 During the Pliocene Epoch, animals such as
bears, dogs, and cats, evolved into modern
forms. Herbivores, such as the giant ground
sloth, flourished.
 Dramatic climatic changes occurred, and the
continental ice sheets began to spread. The
Bering land bridge and the Central American
land bridge formed, allowing various species to
migrate between the continents.
The Pleistocene Epoch
 During the Pleistocene Epoch, ice sheets in Europe and
North America advanced and retreated several times.
 Some animals had certain features that allowed them
to survive the cold climate, such as the thick fur that
covered woolly mammoths.
 Other species survived by moving to warmer regions,
while some species eventually became extinct.
 Fossils of the earliest ancestors of modern humans
were discovered in Pleistocene sediments.
 Evidence of more-modern human ancestors indicated
that early humans may have been hunters.
The Holocene Epoch
 The Holocene Epoch began as the last glacial
period ended. As the ice sheets melted, sea
level rose about 140 m, and the coastlines took
on their present shapes.
 Modern humans developed agriculture and
began to make and use tools made of bronze
and iron.