Focus On Life Science

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Lesson 1 Relative Ages of Rocks Lesson
2 Absolute Ages of Rocks
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lesson.
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7.1 Relative Ages of Rocks

• uniformitarianism
• rock cycle
• clast
• lithification
• stratum
• superposition
• relative age

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The Beginning of Modern Geology
7.1 Relative Ages of Rocks

• James Hutton was the first person to realize that
  one process formed rock and another process tore
  it down.

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The Principle of Uniformitarianism
7.1 Relative Ages of Rocks

• Scientists can observe the processes that are
  active today, and interpret what happened in the
  past.

• Uniformitarianism states that the same Earth
  processes have been at work for a very long time.

• Geological processes that are at work today were
  also at work in the past.
• Geological processes are so slow that direct
  observation is not possible.

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The Rock Cycle
7.1 Relative Ages of Rocks

• The rock cycle is a series of processes that make
  and change rocks through

• heating
• melting
• cooling
• uplift

• weathering
• burial
• increasing pressure

Metamorphosis
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The Rock Cycle (cont.)
7.1 Relative Ages of Rocks
How are materials from the earth broken down?
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The Rock Cycle (cont.)
7.1 Relative Ages of Rocks
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Three Major Types of Rocks
7.1 Relative Ages of Rocks

• Igneous rocks

• produced when magma solidifies
• Metamorphic rocks
• any rock that is put under extreme pressure or
  heat
• Sedimentary rocks
• form from compacted and cemented sediments

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Sediment Formation and Layering
7.1 Relative Ages of Rocks

• Sedimentary rocks form from preexisting rocks.

• Four steps in the formation process
• Weathering
• Transportation
• Deposition
• Lithification

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Weathering
7.1 Relative Ages of Rocks

• Weathering is the physical or chemical breakdown
  of rocks into smaller pieces.

• Physical weathering breaks down rocks without
  changing the mineral composition.
• Chemical weathering changes the mineral
  composition of rocks.

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Weathering (cont.)
7.1 Relative Ages of Rocks
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Transportation
7.1 Relative Ages of Rocks

• Transportation occurs when sediments move
  downhill to lower areas and come to rest.

• Clasts, different-sized sediments such as large
  boulders to microscopic bits of rocks that
  require different amounts of force to move them.

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Deposition
7.1 Relative Ages of Rocks

• Deposition occurs when sediment being
  transported by water, wind, or a glacier slows
  down or stops.

• This usually happens in low areas called
  depositional environments.
• Two characteristics are parallel, horizontal
  layers, and sorting.

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Lithification
7.1 Relative Ages of Rocks

• Lithification occurs when older sediment layers
  become compacted beneath younger layers.

• Mineral-rich liquids seep into the pore spaces
  between the sediment grains.
• The water evaporates and the minerals are left
  behind to cement the grains together.

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Superposition and the Fossil Record
7.1 Relative Ages of Rocks

• Layers of rocks are called strata.

• Four principles help geologists study strata and
  interpret the rocks history.
• Superposition

• Original horizontality
• Original lateral continuity
• Cross-cutting relationships

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Principle of Superposition
7.1 Relative Ages of Rocks

• In a stack of undisturbed sedimentary rock
  layers, the layers on the bottom were deposited
  before the layers on top.

• Relative age tells how old something is when
  compared to something else.

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Remaining Principles
7.1 Relative Ages of Rocks

• Original horizontality

• Rock layers are originally deposited in
  horizontal, or nearly horizontal, layers.
• Original lateral continuity
• Sedimentary rocks form layers that cover large
  areas.
• Cross-cutting relationships
• A layer or feature that cuts across other rock
  layers is younger than the layer(s) being cut.

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Fossils and Relative Age
7.1 Relative Ages of Rocks

• Geologists keep track of which fossils came from
  which strata and apply the principle of
  superposition.

• Fossil occurrences in layers are used to confirm
  or assign relative ages to rock strata.

Stenos Principles
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Lesson 1 Review
7.1 Relative Ages of Rocks

1. A
2. B
3. C
4. D

What principle states that processes at work
today are the same processes that occurred in
Earths past? A superposition B relative
age C original lateral continuity D uniformitari
anism
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Lesson 1 Review
7.1 Relative Ages of Rocks

1. A
2. B
3. C
4. D

What type of rock is formed when put under
extreme pressure or heat? A igneous B metamorphic
C strata D sedimentary
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Lesson 1 Review
7.1 Relative Ages of Rocks

1. A
2. B
3. C
4. D

What process slows or stops sediments in low
areas of the landscape? A deposition B lithificati
on C weathering D transportation
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End of Lesson 1
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7.2 Absolute Ages of Rocks

• isotope
• radioactive decay
• half-life

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What is Earths Age?
7.2 Absolute Ages of Rocks

• Scientists discovered and used a natural clock
  to date the age of Earth, meteorites, and the
  moon.

• Scientists used this natural clock to determine
  the age of bog bodies.

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Atoms and Isotopes
7.2 Absolute Ages of Rocks

• Atoms are the microscopic building blocks of all
  matter on Earth.

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Atoms and Isotopes (cont.)
7.2 Absolute Ages of Rocks

• An isotope is the term for atoms of an element
  that have the same number of protons, but a
  differing number of neutrons.

• Carbon isotopescarbon-12, carbon-13,
  carbon-14have 6, 7, or 8 neutrons.

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Radioactive Decay
7.2 Absolute Ages of Rocks

• Radioactive decay occurs when an unstable nucleus
  changes into another nucleus by emitting
  particles and energy.

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Parent and Daughter Isotopes
7.2 Absolute Ages of Rocks

• The isotope that undergoes radioactive decay is
  the parent isotope.

• The stable form of the element that forms is the
  daughter isotope.

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Half-Life
7.2 Absolute Ages of Rocks

• Parent isotopes decay into daughter isotopes at a
  constant ratethe decay rate.

• The half-life of an element is the calculated
  length of time it takes for half a specific
  amount of a parent isotope to decay.

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Half-Life (cont.)
7.2 Absolute Ages of Rocks
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Radiometric Dating
7.2 Absolute Ages of Rocks

• Scientists use radiometric dating to calculate
  absolute ages of rocks and minerals.

• Comparing the amount of parent to daughter
  material determines the number of half-lives the
  material has been through.
• Igneous rock is most commonly used for
  radiometric dating.

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The Absolute Age of Earth
7.2 Absolute Ages of Rocks

• Rock grains from continental shieldswhere the
  oldest rocks on Earth occurare estimated to be
  4.0 to 4.4 billion years old.

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Meteorites and the Moon
7.2 Absolute Ages of Rocks

• Scientists used radiometric dating to determine
  the ages of meteorites and the Moon.

• The closeness of calculated ages of Earth, the
  Moon, and meteorites helps confirm that the
  entire solar system formed at the same time.

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Lesson 2 Review
7.2 Absolute Ages of Rocks

1. A
2. B
3. C
4. D

The isotopes of an element have a different
number of what? A protons B neutrons C electrons D
atoms
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Lesson 2 Review
7.2 Absolute Ages of Rocks

1. A
2. B
3. C
4. D

What important feature of radioactive decay has
allowed geologists to date Rocks? A the isotopes
of an element may be stable or unstable
B the nucleus gains or loses protons C parent
isotopes decay into daughter isotopes D the
decay occurs at a constant rate
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Lesson 2 Review
7.2 Absolute Ages of Rocks

1. A
2. B
3. C
4. D

What do scientists use to measure the absolute
age of a rock? A radiometric dating B amount of
carbon in the rock C absolute dating
D relative dating
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End of Lesson 2
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Chapter Resources Menu
Chapter Assessment California Standards
Practice Concepts in Motion Image Bank Science
Online Interactive Table Virtual Lab BrainPOP
Click on a hyperlink to view the corresponding
feature.
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Chapter Assessment 1

1. A
2. B
3. C
4. D

How can the rounded peaks of older mountain
ranges be explained? A erosion B weathering C upli
ft D deposition
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Chapter Assessment 2

1. A
2. B
3. C
4. D

What term describes the physical or chemical
breakdown of rocks into smaller
pieces? A deposition B erosion C lithification D w
eathering
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Chapter Assessment 3

1. A
2. B
3. C
4. D

What principle states that the bottom layers of
sedimentary rocks were deposited before the top
layers? A lithification B uniformitarianism C supe
rposition D original horizontality
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Chapter Assessment 4

1. A
2. B
3. C
4. D

What type of rock is most commonly used in
radiometric dating? A metamorphic B igneous C sedi
mentary D minerals
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Chapter Assessment 5

1. A
2. B
3. C
4. D

What term describes time it takes for a sample of
a radioactive isotope to decay to half its
original mass? A absolute age B half-life C radiom
etric dating D relative age
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CA Standards Practice 1

1. A
2. B
3. C
4. D

What process includes heating, melting, cooling,
uplift, weathering, and increasing
pressure? A sediment formation B metamorphic rock
formation C igneous rock formation D the rock
cycle
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CA Standards Practice 2
SCI 4.c

1. A
2. B
3. C
4. D

What does the principal of original lateral
continuity state? A layers on the bottom are
deposited before layers on the top
B sediments are deposited horizontally
C sedimentary rocks form layers that cover
large areas D sediments always remain
horizontal
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CA Standards Practice 3
SCI 4.c

1. A
2. B
3. C
4. D

Which type of rock is the most useful for
relative dating? A igneous B sedimentary
C magma D metamorphic
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CA Standards Practice 4
SCI 4.d

1. A
2. B
3. C
4. D

Which describes a daughter isotope? A decays into
a parent isotope B is an unstable form of
the parent isotope C is the result of parent
isotope decay D is heavier than its parent
isotope
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CA Standards Practice 5
SCI 4.d

1. A
2. B
3. C
4. D

What percentage of parent isotope remains after 2
half-lives? A 75 B 30 C 37.5 D 25
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Concepts in Motion 1
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Concepts in Motion 2
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Image Bank
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Interactive Table
Stenos Principles
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End of Resources