Integrated Science
Unit 10, Chapter
28

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.


Original Heat – this is the left over heat of Earth’s creation from the bombardment of meteorites and asteroids. Only about 1% left
 Friction between atoms – this heat is generated by gravity squeezing the Earth into its sphere shape. Accounts for about 40% of heat
 Radioactive decay – the breakdown of radioactive isotopes like uranium provides the
Earth with most of its internal heat, about 60%.

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 10 – 80km
Density 2.75 g/cm 3
Oldest Known
5 – 10km
3.0 g/cm 3
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.

 The apparent movement of the continents relative to one another over the Earth’s crust.

 1 st 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)

 2 nd 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!!

 3 rd 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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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, intermediate and deep EQ, volcanoes occur

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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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.

 Epicenter – point on earth’s surface where the EQ waves touch surface first.

Northridge,
California in
January 1994.
 Focus – point inside crust where the
EQ movement first occurred.

 Seismic waves – common name given to all EQ waves.
 Hawaii earthquake damage

Worldwide Earthquakes
Notice- most earthquakes occur on plate boundaries.

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