Download Structure of the Earth

Structure of the Earth
Crust
Mantle
Outer core
Inner core
The Earth’s Crust
The earth is made up of four main layers:
1. The Crust – thin layer of solid rock covering
the earth (5 to 70 km thick).
• This crust is thinner under the oceans
(oceanic crust) and thicker under the
continents (continental crust).
• The crust is broken into pieces that “float” on
the Earth’s mantle and are always moving.
2. The Mantle – the largest layer.
•
•
upper mantle is mostly solid rock
lower mantle is partly melted rock (it is
closer to the hot core)
3. The Outer Core – so hot that it is in
liquid form.
4. The Inner Core – the deepest and
hottest layer of the earth..
How do we know about the
Earth’s layers?
Scientists gather evidence and make guesses
based on technologies like:
 sonar,
 magnetometers,
 seismographs,
 satellite imaging and
 core samples from deep sea drilling.
Theory of Continental Drift
 Alfred Wegener (1880-1930), a German
meteorologist, noticed that the continents fit together
like puzzle pieces.
 He proposed a theory as to how the continents
move:
The Theory of Continental Drift states that the
continents are very slowly but constantly moving - a
few centimeters each year.
http://www.youtube.com/watch?v=GYVS_Yh6dTk
Wegener’s Evidence of
Continental Drift
1.
Paleogeographic Evidence (Shape of the continents)
Wegener noticed that the continents are shaped to sort of fit
together.
He thought that all the continents used to fit together in one big
continent called Pangaea which broke apart about 200 million
years ago into the continents that we now know.
2. Biological evidence (Fossils)
Wegener noticed that fossils of the same animals could be found
on different continents, for example:
Avalon Peninsula and Wales (in Britain) are 4000km away from
each other but the same animals have been founding both
places!
3. Geological evidence ( Rocks and rock layers)
Wegener noticed that geologists have found similar rocks on
both sides of the Atlantic:
The Appalachian mountain range in eastern North America
were formed the same way, are the same age AND are made
up of the same rocks as the mountain range that goes through
Britain and Norway.
4. Meteorological Evidence
(Climate Change)
But coal (formed from dead
plants and animals in a tropical
environment) can be found in
colder climates like Canada,
Europe and even Antarctica!
Some places that now have
warm climates like Africa and
India have evidence that
glaciers once covered them.
 Even with all the evidence Wegener
found that supported his Theory of
Continental Drift, he couldn’t figure out
how the continents moved.
 Because of this, other scientists never
did believe him. They believed that the
continents were fixed in place.
Technologies Which Gather
Evidence From The Sea Floor

In more recent years, new
technologies have been developed
that allows scientists to gather more
evidence from the sea floor.
1. Sonar
2. Magnetometers
3. Deep sea drilling
Sonar
1. Sonar – is used to map the depth and features of
the sea floor using sound waves.
Sonar
They found features that were the same as
found on land, including mountains, and one
particular mountain range called the Mid
Atlantic Ridge.
Magnetometers
2. Magnetometers – detect the strength and
direction of a magnetic field.
Remember that igneous rock is made from
magma and when it cools the iron (magnetite)
stays in line with the magnetic field of the
earth. This provided evidence that the sea
floor is spreading.
Magnetometers
 Scientists noticed the
direction of the
magnetic field changed
from north to south and
back again in a pattern
that looked like
stripes… and they
were parallel to the
Mid-Atlantic Ridge.
Deep sea drilling
3. Deep sea drilling – core samples of rock
taken by drilling into the oceanic crust.
Drilling has shown that younger rock is closer
to the Mid-Atlantic Ridge and older rock is
farther away and closer to the continents –
more evidence that the sea floor is spreading.
Plate tectonics
 Since the sea floor is moving as well as the
continents, the old theory of Continental Drift
needed to be updated.
 The new theory is called Plate Tectonics
which means the earth’s crust is broken up
into plates that are always moving around the
earth’s mantle. The crustal plates are made
up of continental crust (the land) and oceanic
crust (the land under the ocean).
Boundaries
 http://school.nelson.com/elementary/sci
ence/bcscienceprobe/0176283110/stud
weblinks.html
Go to Ch8 (8.2) Mountain Maker, Earth
Shaker
Divergent Boundaries
 Places where newly formed rocks pull
the plates apart, like in the Mid-Atlantic
Ridge, are called Divergent
Boundaries.
Convergent boundaries
 Places where plates push together, like
in Japan, are called Convergent
boundaries.
Transform Boundaries
 Places where plates slide past each
other are called Transform
Boundaries.
Convection Currents
 One theory for why continents move
has to do with convection currents in the
mantle under the earth’s crust that
move the plates.
 Remember that hot air rises and cool air
sinks – this is called convection. The
same happens with liquids like magma.
Subduction Zone
 The area where one plate is pulled
under another is called a Subduction
Zone.
 Magma heats up in the inner mantle,
moves to the outer mantle, and moves
along under the plate above it.
 As that cools, it sinks back down,
moving the crust on top of it along like a
conveyor belt.
Canadian scientists who have made a
contribution to local, regional and
global geology:
1. J. Tuzo Wilson
2. Joseph Tyrell
3. Harold Williams
J. Tuzo Wilson
 J. Tuzo Wilson
mapped out where
earthquakes and
volcanoes had
occurred over the
earth’s surface
helping to define the
earth’s plates.
Joseph Tyrell
 Joseph Tyrell
discovered
dinosaur fossils in
Alberta that proved
that the local
climate was
warmer at an
earlier time
Harold Williams
 Harold Williams talked about the plate
tectonic activity along the eastern edge
of the North American continent.