Transcript Notes Chapter 28

Integrated Science
Unit 10, Chapter
28.1 Understanding Earth
 Geology
is the study of
rocks and materials that
make up Earth and the
processes that shape it.
 In
1666, Nicholas Steno
(1638-87) noticed that
shark’s teeth resembled
mysterious stones called
“tonguestones” that were
found in local rocks.
28.1 Understanding Earth
 Steno’s
explanation helped
him develop ideas about how
rocks and fossils form.
 These
ideas are used in a
technique called relative
dating.
 Relative
dating is a way to
put events in the order in
which they happened.
What happened here and
in what order?
28.1 Understanding Earth
 The
approximate age of each layer of a rock
formation can be determined by applying
Steno’s idea called superposition.
A
stack of newspapers
illustrates superposition.
 Superposition
means that
the bottom layers of rock
are older than the layers on
the top, unless they have
been disturbed.
28.1 Understanding Earth

Original horizontality states that sediment particles fall to
the bottom of a basin, such as a riverbed, in response to
gravity and result in horizontal layers.
28.1 Understanding Earth


Lateral continuity is the idea that layers of sediment
extend in all directions when they form and before they
become rock layers.
The idea of lateral
continuity states that
layers of rock are
continuous unless a
geologic event like a river
interrupts the layers or an
earthquake offsets them.
28.1 Understanding Earth
 Another
important idea, developed by Scottish
geologist James Hutton (1726-97), is that the
"present explains the past."
 The
idea of crosscutting relationships
states that a vein of
rock is younger than
the rock that
surrounds the vein.
vein
28.1 Understanding Earth


Sometimes rock pieces called inclusions are contained
in another rock.
During the formation of a
rock with inclusions,
sediments or melted rock
surround the inclusion and
then become solidified.
 Therefore, the inclusions
are older than the
surrounding rock.
28.1 Understanding Earth

Over geologic history,
many animals and plants
have lived and become
extinct.

Their remains have
become fossils.

The idea of faunal
succession states that
fossils can be used to
identify the relative age of
layers of a rock formation.
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28.1 Calculating Earth's Age
William Thompson Kelvin
(1824-1907), known for
proposing the absolute
temperature scale that came to
be named after him,
meticulously calculated Earth’s
age to be between 10 million
and 100 million years.
 Lord Kelvin’s calculation was
not accurate because he did
not realize that Earth has
internal heat from the core and
radioactive decay.

Earth’s 3 “internal”
heat sources
Heat – this is the left over heat of Earth’s
creation from the bombardment of meteorites
and asteroids. Only about 1% left
 Original
between atoms – this heat is generated
by gravity squeezing the Earth into its sphere
shape. Accounts for about 40% of heat
 Friction
decay – the breakdown of
radioactive isotopes like uranium provides the
Earth with most of its internal heat, about 60%.
 Radioactive
28.1 Calculating Earth's Age

Today Earth’s age has been
given by measuring the
radioactive decay of uranium
into lead. Absolute dating

As techniques and evidence
from tree rings and glaciers,
and rock layers, improved
Earth’s age has been
determined to be about 4.6
billion years.
28.1 The Layers of the Earth

Earth’s surface is covered with a thin crust.

There are two kinds of crust:
— continental
— oceanic
Continental Crust
Oceanic Crust
Average Thickness
Density
Oldest Known
10 – 80km
5 – 10km
2.75 g/cm3
3.0 g/cm3
4.28 B.Y. (Hudson Bay) 200 M.Y.
Composition
Granite
Basalt
28.1 Convection inside Earth

The rocky material of the
mantle moves in very slow
convection currents.

This movement is related to
density and temperature
differences in the mantle.

Hot material is less dense
and rises.

Cold material is denser and
sinks.
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28.2 Continental Drift

In 1915, Alfred Wegener (1880-1930), a German
meteorologist, wrote a book titled The Origin of
Continents and Oceans.

Wegener gathered evidence that supported his idea that
all the continents had been connected.
Continental Drift
The
apparent movement of the
continents relative to one another
over the Earth’s crust.
1st
evidence: Fit of the continents.
— He cut out and pieced together a
crude map.
— He called the great ocean
Panthalassa (meaning all seas)
— The continent was called Pangaea
(meaning all lands)
2nd
body of evidence: Matching
rocks:
Found on these continents.
— 1. North Eastern N. America & Western
Europe.
— 2. Southern N. America & North Africa.
— 3. South America & Africa.
— 4. Not enough proof!!
3rd
body of evidence Identical fossils
found all over the world:
—
1. East South America & West Africa.
— 2. Southern North America & Northern
Africa.
—
3. Northern North America and Europe.
pangaea animation
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next day
28.2 Plate Tectonics

Theory of plate tectonics, started in
1965, and explains the movement of
continents and other geological
events, like earthquakes and
volcanoes through the movement of
giant plates of rock called tectonic
plates.

Tectonics means construction or
building.
28.2 Sea Floor Spreading

In the early 1960s, Henry
Hess (1906-69), a geologist
and former commander of a
Navy ship equipped with an
echo sounder, used the
profile of the sea floor to
propose that it was
spreading at the mid-ocean
ridges.

An echo sounder is
used to make a profile
of the sea floor.
28.2 Sea Floor Spreading

At the same time, Robert
Dietz (1914-95), a
scientist with similar
ideas, coined the term
sea-floor spreading.

Sea-floor spreading says
the sea floor on either
side of a mid-ocean ridge
is moving away from the
ridge and creating a rise
or valley.
28.2 Sea Floor Spreading

Magma from the mantle enters the rise or valley and
cools, creating new oceanic crust).
28.2 Magnetic Patterns

Over eons the magnetic
polarity of Earth switches,
(North South)

Scientists believe the poles
switch because of a magnetic
interaction between the
planet’s inner and outer core.

In the 1950s and 1960s,
scientists discovered that the
rocks of the sea floor have a
very interesting magnetic
pattern.
28.2 Magnetic Patterns
 Stripes
of rock with a
north-south
orientation (normal)
alternate with stripes
of rock with a southnorth orientation
(reversed).
 This
striping tells us
7 important things.
28.2 Magnetic Patterns

First, it tells us the Earth’s magnetic field
changes about every 100,000 years.

Second, it tells us the ocean crust is being
constantly recycled

Third, it tells us the newest crust is at the
center of the ridge or rise.

Forth, it tells us the most heat is being
released from the Earth’s interior at the
center of the ridge or rise.

Fifth, it tells us the direction the convection
currents move, under those plates

Sixth, it tells us the speed of the convection
currents.

Seventh, it tells us if new plate is being
created here, the oldest ocean crust must
be being destroyed somewhere.
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28.2 Describing Plate Boundaries
 There
—
—
—
are three main kinds of plate boundaries:
divergent
convergent
transform
28.2 Plate Tectonics

Tectonic plates are pieces of lithosphere that fit
together and “float” on the asthenosphere.

There are a number of large tectonic plates on Earth’s
surface, and many smaller plates are being identified all
the time.
Can you identify which of the plates are only made of oceanic crust?
Section 28.2 Plate Boundaries
Divergent Boundary– where 2 plates are pulled
apart. In this picture 2 ocean crusts.
 Here
hot less dense magma rises up through
the asthenosphere toward surface, causing the
convection currents, & undersea EQs
 MID-OCEAN
RIDGE -string of undersea
divergent boundaries where new ocean crust is
formed.
 Called
spreading centers & are associated with
mountainous areas on ocean floor
 Earthquakes,
volcanoes, rifts common
28.2 Divergent Plate Boundaries
 Diverging
plates move apart and new crust forms.
28.2 Divergent Plate Boundaries

Divergent boundaries
are sites of
earthquakes and
volcanic activity.
 Mid-ocean ridges and
associated sea-floor
spreading occur at
divergent plate
boundaries.

In effect, a mid-ocean
ridge is like a very long
volcano.
Plate Boundaries Convergent
 Where
2 plates collide by moving together.
 SUBDUCTION
ZONE area where an ocean plate
dives or sinks under another ocean plate, or
continental plate.
 Old
crust is subducted and destroyed here.
Dives into the Asthenosphere, melts then rises
and circulates again.
 Volcanic
islands & trenches are the most
common landforms. EQ of all depths occurs
 Volcanoes
common This is 2 Ocean crusts.
Plate Boundaries Convergent
 This
is an oceanic and continental plate
subduction zone.
 The
plates move toward each other.
 Volcanoes
& trenches are most common
landforms.
 Magma
is generated at all subduction zones
where dense oceanic plates are pushed under
lighter continental plates, melted, and rises
back up through the crust.
 Shallow,
occur
intermediate and deep EQ, volcanoes
Plate Boundaries
 This
convergent boundary is where 2 continental
crusts collide.
 The
rock layers are folded and bent forming
mountains.
 The
plates move toward each other.
 Mountains
and Valleys are the common land
forms
 Volcanoes
rare
28.2 Convergent Plate Boundaries

Convergent plate
boundaries occur where
two plates approach
each other.
 One result of two plates
converging is
subduction.
 A deep oceanic trench
marks the boundary
between a subducting
and an overriding plate
at a convergent
boundary.
Plate Boundaries Transform
Plate Boundaries Transform
 This
boundary is a lateral boundary where two
plates slide past each other.
 Earthquakes
occur frequently at these
boundaries.
 The
plates can move in same direction but at
different rates. Many rolling hills and shallow
trenches are common.
 ANY
TYPE OF CRUST, transform is most
common on earth.
28.2 Movement of Plates

The movement of tectonic plates is related to the
distribution of heat by convection currents in the mantle.
28.2 Plate Tectonics
Key Question:
 What
will Earth look like in 50 millions
years?
*Read text section 28.2 BEFORE Investigation 28.2
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next days notes
28.3 Earthquakes

As tectonic plates move, friction
causes rock at plate boundaries to
stretch or compress, this causes
rocks to store energy.

When the rocks break, change
shape, or decrease in volume, the
stored energy is suddenly
converted to kinetic energy and an
earthquake occurs.
28.3 Earthquakes

A seismograph measures
earthquakes, and
seismologists use seismic
waves to study Earth’s
internal structure.

This is similar to how a
doctor uses X rays to look
at bone structure.
28.3 Earthquakes

The majority of
earthquakes occur at the
plate boundaries.

Earthquakes also occur at
a fault.

Fault - a place crack in
rocks along which
movement occurs.
Earthquake
Terms
–
point on earth’s
surface where
the EQ waves
touch surface
first.
Epicenter
Northridge,
California in
January 1994.
– point inside crust where the
EQ movement first occurred.
Focus
waves –
common name
given to all EQ
waves.
Seismic

Hawaii earthquake damage
Worldwide Earthquakes
Notice- most earthquakes occur on plate boundaries.
2 Categories of
Seismic Waves
Body & Surface
P waves

Short for Primary waves
 Fastest
and First body wave recorded by a
seismograph (17,000 mph)
 Travel
through solids and liquids (generate sound)
 Faster
through more rigid material
 They
—
are Compression waves
Cause rock particles to move
together and apart along the
direction of the waves
P-Wave movement
S waves
short for
Secondary Waves
 Second
body wave recorded
by a seismograph (8,000 mph)
 Only
travel through solids
 Can’t
be detected on the side of the
earth opposite the earthquake’s
epicenter.
 They
—
are Shear waves
Cause rock particles to move up & down
or side to side (right angle) to the
direction in which the waves are
traveling
S-Wave movement
Surface Waves
 Slowest
moving wave & last to be
recorded by seismograph
 Travel
similar to ocean waves
 Cause
the surface to rise, fall, turn
and twist
 Very
destructive: especially in loose
earth
2 Types of Surface waves
 Love
Waves (5,000 mph)
 Fastest
kind of surface wave is called a Love
wave , (named for A.E.H. Love, a British
mathematician)
 Love
worked out the mathematical model for
this kind of wave in 1911.
 It
moves the ground from side-to-side.
2 Types of Surface waves
 Rayleigh
Waves (4,000 mph)
 Slower
kind of surface wave (named for John
William Strutt, Lord of Rayleigh
 Rayleigh
predicted mathematically the
existence of this kind of wave in 1885.
 It
moves the ground up & down and side-toside rolling the ground like waves on water.
 Most
of the shaking felt from an earthquake is
due to the Rayleigh wave, which can be much
larger than the other waves
Surface Waves movements
28.3 Earthquakes in the U.S.
 The
west coast of U.S.
experiences most
earthquakes because
of the San Andreas
fault a boundary
between Pacific and
North American Plate,
and the 10,000 +
smaller faults.
 The
Midwest and
Eastern U.S. does
experience EQ but
they are more rare.
28.3 Earthquakes in the U.S.

Minor earthquakes release
stored energy in small, less
destructive amounts.

Rocks in areas that do not
experience frequent small
earthquakes may have a lot
of stored potential energy.

When this potential energy
is finally converted to kinetic
energy, the earthquake could
be big.
28.3 Earthquake Safety
 Get
outside to an open area (if possible), far
from buildings and objects that could fall. Sit
down to avoid falling.
 If
you are inside: Drop, cover, and hold.
28.3 Preparing for Earthquakes

A huge wave generated by an underwater earthquake
or landslide is called a tsunami.
 The speed at which this wave travels can be about 700
kilometers per hour. (435MPH)
28.3 Earthquakes
Key Question:
 What
mechanical factors affect earthquakes?
*Read text section 28.3 BEFORE Investigation 28.3