Transcript Plate Tectonics

The Inner Earth
Continental Drift
Convection Currents, and
How Heat Works
Chapter 5
The Earth does not look the same today as it did millions of
years ago because it’s surface has been lifted up, pushed down,
bent, and broken apart.
Scientists use both direct and indirect evidence to study the inside
of the earth.
Direct evidence- rock samples
Indirect evidence- seismic waves through the earth
Rock samples can tell us what the conditions may have been like on
Earth when the rock formed.
Seismic waves
Geologists can measure the speed at which the waves travel through
the earth to determine the structure of the planet.
Just as you may knock on a wall to find a stud while hanging a picture.
It sounds hollow if there is nothing behind it; and solid if there is.
A Journey to the center of the Earth
Temperature
As you travel toward the center of the earth it gets hotter because
you are getting closer to the core, just as you get warmer the
closer you get to a camp fire.
The center of the Earth is hot because of two reasons:
1. There is leftover heat from the formation of the planet billions
of years ago
2. The main reasons is because of radioactive materials decaying
in the core. The core is basically a nuclear reactor.
Pressure
Pressure increases the deeper you go because there is more and
more weight on top. If you go down one mile, there is a mile of
rock above pushing down. Fabulous
The Crust
The crust is the outer layer of rock that forms the outer skin
that includes dry land and the ocean floor.
The crust beneath the ocean is called the oceanic crust it is
made from basalt.
In most places the crust is between 5 and 40 km thick. It can
be up to 70 km thick under mountains.
The Mantle
The mantle is made up of very hot rock but solid. It is divided up
into layers depending on the physical characteristics of that layer.
The mantle is approximately 3,000 km thick.
The lithosphere is the uppermost part of the mantle similar to the
crust. Approximately 100 km thick.
The asthenosphere is the soft part of the mantle just below the
lithosphere.
The lower mantle is beneath the asthenosphere and extends all the
way to the core.
The Core
The core consists of two parts, the inner and outer. It is made
mostly of the metals iron and nickel.
-The outer core is liquid
-The inner core is solid
Together the core is approximately 3, 486 km thick.
The immense pressure does not allow the inner core to become
a liquid.
The core and the Earth’s magnetic field
Scientists believe the earth’s magnetic field is caused by the
movements in the liquid outer core.
Section 2: Convection and the Mantle
Lets first discuss what heat is: Heat is the movement or vibration
of molecules within a substance. The faster they move the hotter
the substance is.
It is important to know that heat will always move from warm to
cold
Types of Heat Transfer
Radiation, Conduction and Convection
Radiation- The transfer of heat energy through space. No direct
contact with anything. Example: Sun and fire.
Conduction- The transfer of heat between objects that are
touching. Examples: a spoon in a hot cup of tea. Your hand
touching the hot handle of a pot on a stove.
Convection- The movement of heat through a fluid (gas or
liquid). The movement depends on the temperature and the
density of the fluid. Hot substances usually rise and cooler ones
sink (Think of a hot air balloon). Examples: Heating water in a
pot. Ocean currents. Movement of air through the atmosphere.
Radiation
Conduction
Convection
http://www.youtube.com/watch?v=7xWWowXtuvA
Convection Currents in the Earth
Heat from the Earth’s core cause convection currents in the
mantle just like water in a pot on the stove. Hotter
substances rise to the surface and cooler ones sink, in this
case magma.
http://www.youtube.com/watch?v=ryrXAGY1dmE
Section 3 pages 136- 140
Drifting Continents
Alfred Wegener theorized that the continents were once all together
and have since drifted apart.
This idea he called Continental Drift.
He believed that about 300 million years ago all the landmasses
were together in one super continent called Pangaea.
http://www.youtube.com/watch?v=lJiAUvB1vEU
Evidence In Support of Wegener’s Idea
There is evidence in land features, fossils, and evidence of
climate change to support Wegener’s hypothesis.
Land Features- Mountain ranges line up and continents seem
to fit together.
Evidence Continued
Fossil evidence- The fossils of the same plants and animals
appear on different continents now separated by oceans.
Wegener also presented some fossil evidence. One was an
animal fossil and the other was a plant fossil. Mesosaurus
was an aquatic dinosaur closely related to the modern
Alligator. Its fossil remains are only found near the eastern
side of South America and the adjoining western side of
Africa when the two continents are positioned side by side.
Hence, Wegener concluded that the best explanation for this
unusual occurrence is that the two continents were once
joined together (or the same landmass), before Mesosuarus
became extinct, until they fractured and drifted away from
each other. Opposing scientists argued that there must have
been a land bridge linking South America and Africa. But no
such evidence for a land bridge across the south Atlantic
Ocean has been observed since.
Evidence Continued
Climate – As a continent moves toward the poles its climate
becomes colder. As a continent moves towards the equator its
climate becomes warmer. The continent will bring with it fossils
from its previous location.
Example: Fossils from tropical plants have been found on an
island in the Artic Ocean. This island must have been originally
located near the equator.
There is also evidence of glaciers on the continent of Africa
indicating it was much colder there in the past. .
Wegener’s Theory Rejected
At the time Wegener could not show evidence of how the
continents moved, so his theory was rejected.
The scientist at he time believed that mountains formed from the
cooling of the Earth. Wegener said that if that was true then
there would be mountains all over the Earth.
Wegener proposed that mountains formed from the collision of
continents.
We now know that the continents move by means of convection
currents in the mantle.
Sea Floor Spreading
Section 4 page 141-147
In the mid- 1900’s scientists used sonar to map the ocean
floor’s topography. They discovered mid ocean ridges which
are like mountains on the sea floor. These mountains look
like seams on a baseball.
Wow, look at this mid- ocean ridge!
In sea-floor spreading, the floor spreads apart along both sides of
a mid-ocean ridge as new crust is added. As a result, the ocean
floors move like conveyer belts.
Evidence from molten material
At the mid ocean ridge, scientists found rocks that look like
pillows and as though it has been squeezed from a tube of
toothpaste.
Evidence of Sea Floor Spreading
There are several types of evidence to support the theory of sea
floor spreading.
1. Eruptions of molten material, magnetic stripes in the rock of
the ocean floor, and the ages of the rocks themselves.
2. Rock samples taken close to the ridge are younger than ones
farther away. (Drilling samples)
Subduction page 146
The sea floor plunges down in what are called deep
ocean trenches. This usually happens at the
continental crust.
The Theory of Plate Tectonics
Section 5
Plate Tectonics
What is plate tectonics?
Plate tectonics is the theory that pieces of the
lithosphere are in motion. It explains the formation ,
movement, and subduction of plates.
The three types of plate boundaries are:
 Divergent boundaries
 Convergent boundaries
 Transform boundaries
Plate Boundaries
Three Types:
Divergent- The area where two plates move apart or diverge.
Convergent- The area where two plates come together or meet.
Transform- The area where two plates move past one another
in opposite directions.
Divergent boundary- where two plates move apart, most occur
along mid- ocean ridges.
Rift valley- when divergent boundaries occur on land
Convergent boundary- A place where two plates come together.
Transform boundary- An area where two plates slip past on
another in opposite directions.
Fault- Breaks in the earth’s crust where rocks have slipped past
each other.
Can you identify the different boundaries here?