Transcript Earth Science

Earth Science
Chapter 4
Plate Tectonics
Evidence from Rock Samples –
Direct (you can hold the rocks)
Evidence from Seismic Waves –
Indirect – speed of waves and their path
are studied
The three main layers of Earth differ in
temperature, composition, pressure and
size.
Temperature – Temperature increases
with depth - heat left over from when earth
formed + radioactive elements release heat
Pressure - Increases with depth weight of rock from above
Earth's Interior
The three main layers of Earth
are the crust,
the mantle,
and the core.
Layers of
the Earth
are similar
to the
layers in a
hardboiled
egg!
The Crust

Solid outer rock – includes land and ocean
floor, 5km – 40km thick (can be 70km beneath
mountains)
Oceanic Crust
• Thinner
• Mostly Basalt
(igneous rock)
• Denser than
continental crust
Continental Crust
• Thicker
• Mostly Granite
(igneous rock)
• Less dense than
oceanic crust
The Mantle – 3000km thick
Lithosphere –
 ‘lithos’ = stone (Greek)
100 km thick
 Rigid
 Uppermost part of mantle and crust

Asthenosphere –
‘asthenes’ = weak
 Bendable + softer + can flow

The Lower Mantle

Solid
The Core - 3486 km thick
Mostly iron and nickel
Outer Core - liquid
Inner Core – dense, solid, extreme
pressure squeezes iron and nickel so much
that they cannot be liquid
Earth’s Magnetic Field
Movements in the earth’s liquid outer core
create a magnetic field. This magnetic field
surrounds the planet
Structure of the earth –
http://www.youtube.com/watch?v=3MFr2cC3erk
Layers of the earth song –
http://www.youtube.com/watch?v=Q9j1xGaxYzY
Convection and the Mantle 4.2
The movement of energy form a warmer
object to a colder object is called Heat
Transfer.
There are three types of heat transfer:
 Radiation
 Conduction
 Convection
Radiation
 Heat
is transferred through space
 No direct contact between heat
source and object
 sunlight, heat around open fire
http://www.youtube.com/watch?v=2JZ
ciWtK6vc&safe=active
Eureka Radiation 4:02 (2:39)
Conduction
Transfers heat by direct contact
 Matter touching matter
 Can occur between any state of matter: solid,
liquid or gas
 Metals are good conductors of heat
 Bad conductors include wood, rubber, glass
 Example: Heat transfers directly from the
element of a stove to a metal pot

http://www.youtube.com/watch?v=wV7gzcKegdU&safe=active
Conduction 2:02
Eureka
Conduction -
Convection
 heat
transfer by the movement of
currents within fluids – liquids and gasses.
 Hotter particles move further apart and
rise (less dense)
 Cooler particles move closer together and
fall (more dense)
 Transfer is therefore vertical (up & down)
 Caused by differences in temperature
and density
http://www.youtube.com/watch?v=ON2Y3FEk_UI&safe=active Eureka Convection 2:06
Convection –.
Convection currents are set in motion
by –
1. Heating and cooling of a fluid
2. Changes in the density of the fluid
3. Force of gravity
2
1
3
3
2
1
1
Convection Currents in the Earth
Happen in the mantle
Caused by heat from the core and the
mantle
Rock in lower mantle is hotter and less
dense than rock in upper mantle .
Hot rock rises
Cools at top mantle
sinks back
Heats up and rises again
Methods of heat transfer  https://www.wisc-online.com/learn/naturalscience/earth-science/sce304/heat-transfer-conduction--convection--radiation

http://openhighschoolcourses.org/pluginfile.ph
p/6926/mod_page/content/1/Week_6_Resourc
es/lsps07_int_heattransfer.swf
Convection in the earth –
http://www.sciencebook.dkonline.com/11.html
Continental Drift C4S3
Wegener's hypothesis was that all the
continents were once joined together in a
single landmass - Pangaea - and have
since drifted apart.
Alfred Wegener
Pangaea – the super continent
Evidence of Continental Drift
Evidence from Land Features
1. Continents fit together like the pieces to a puzzle
 2. Mountain ranges on Africa and South America line up
 3. European coal fields line up with North American coal fields.

2. Fossil evidence of dinosaurs and
prehistoric plants – Glossopteris,
Mesosaurus, Lystrosaurus
3. Ancient Climatic Zones – fossils and rocks
a.
Spitsbergen – an island in the Arctic
Ocean - once had a warm climate –
tropical plants found – island was close
to the equator about 300 million years
ago, then moved
b.
South Africa - rocks and sediments left
behind by glaciers. Continental drift had
moved South Africa away from South
Pole
Sea-Floor Spreading C4L4
The longest chain of
mountains in the world
is the system of midocean ridges –
explored with sonar
and deep diving
vessels (Hess WWII)
Iceland is a part of the midocean ridge that rises above
water
In sea-floor spreading, the sea floor spreads
apart along both sides of a mid-ocean ridge
as new crust is added. As a result, the
ocean floors move like conveyor belts,
carrying the continents along with them.
At the mid ocean ridge, a crack develops.
2. Molten material from deep below earth
erupts.
3. As it cools, it forms a strip of solid rock in
the center of the ridge.
4. When more molten material comes out, it
pushes this rock outwards.
5. New strip of rock is formed.
6. This produces basalt – the rock that
forms oceanic crust
1.
Sea floor spreading animation –
 http://earthguide.ucsd.edu/eoc/teachers/t
_tectonics/p_seafloorspreading.html

Evidence of Sea-Floor Spreading
Evidence supported the theory of seafloor spreading: eruptions of molten
material, magnetic stripes in the rock of
the ocean floor, and the ages of the
rocks themselves.
1. Molten Material - shape of rocks –
only when molten material hardens
quickly under water
 Magnetic
Stripes - patterns in rocks a. rocks of ocean floor contains iron
b. as this rock cools, the iron atoms become
magnetized and line up in the direction of
the earth’s magnetic poles
c. When the magnetic polarity of the earth
changes, the new strip shows new
polarity
d. When scientists studied rocks on both
sides of ridge, they found strips of rocks
alternating on each side in the same way
3. Drilling Samples – age of rocks –
the youngest rock was at the center of
the ridge, the older rocks were farther
away. The farther away from the ridge
the rocks were taken, the older they
were.
Subduction
Deep Ocean Trenches – deep under water
canyon where ocean floor sinks
1.
2.
3.
4.
5.
6.
Ocean floor near a mid-ocean ridge is new and
hot – it moves away towards a deep-ocean
trench
As it moves away, it cools – becomes more
dense.
Gravity pulls this denser, cooler floor down
beneath the trench
Ocean floor sinks back into the mantle
Giant conveyor belt – material comes up at
the ridge, moves across ocean floor, sinks at
trench
Takes tens of millions of years
Animation of subduction http://earthguide.ucsd.edu/eoc/teachers/t_tecton
ics/p_subduction.html
http://education.nationalgeographic.com/educati
on/encyclopedia/ocean-trench/?ar_a=1
It takes 200 million years for new rock to form at
mid-ocean ridge, move across ocean, and sink
into deep-ocean trench
Pacific Ocean is shrinking - has many deep ocean
trenches at edges of continents - subduction
occurs faster than new rock is formed
Atlantic Ocean expanding – fewer deep ocean
trenches – as ocean floor spreads, pushes
continents – has nowhere to go
The Theory of Plate Tectonics
• Pieces of the lithosphere are in
slow, constant motion driven by
convection currents in the mantle
• It explains the formation,
movement, and subduction of
Earth's plates (cracks in the
lithosphere)
• Convection currents in the mantle
cause plate motion
Plate Boundaries
 There
are three kinds of plate boundaries:
 Divergent:
spreading boundaries
 Convergent:
 Transform:
colliding boundaries
sliding boundaries.
Divergent: Spreading Boundaries
• Two plates move apart
• Can be found at mid ocean ridges where sea
floor spreading happens (Ocean floor)
• Spreading boundaries on land produce rift
valleys example Great Rift Valley in East Africa
(deep crack in the African
continent)
• Oceanic crust is created
•
•
•
https://www.classzone.com/books/earth_science/terc/content/visualizations/es0804/es0804page01.cfm?chapt
er_no=visualization
https://www.youtube.com/watch?v=ZzvDlP6xd9o
http://www.wwnorton.com/college/geo/egeo2/content/animations/2_1.htm
Convergent: colliding boundaries
Two plates come together
 Density of the plates decides which one will be
on top
 Oceanic crust is destroyed
 Three types of collision plates

Two Oceanic Plates
Meet at a trench
 The denser plate sinks (subducts) under the
other plate (as the ocean floor undergoes sea
floor spreading, it becomes cooler and denser)

Oceanic Continental Plates
The denser oceanic plate sinks (subducts)
beneath the less dense continental plate
Two Continental Plates
Two continental plates collide
 Neither is more dense so no subduction
 Forms mountain ranges (example
Himalayas)

Transform: sliding boundaries
 Two
plates slip past each other
moving in opposite directions
 Crust
is neither created nor destroyed