1. Structure of the Earth
Crust
Mantle
Outer core
Inner core

2. The Earth’s Crust The earth is made up of four main layers:
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.

3. The Mantle – the largest layer.
upper mantle is mostly solid rock
lower mantle is partly melted rock (it is closer to the hot core)
The Outer Core – so hot that it is in liquid form.
The Inner Core – the deepest and hottest layer of the earth..

4. 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.

5. Theory of Continental Drift
Alfred Wegener ( ), 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.

6. 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.

7. 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!

8. 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.

9. 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.

10. 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.

11. 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.
Sonar
Magnetometers
Deep sea drilling

12. Sonar
1. Sonar – is used to map the depth and features of the sea floor using sound waves.

13. Sonar They found features that were the same as
found on land, including mountains, and one
particular mountain range called the Mid
Atlantic Ridge.

14. 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.

15. 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.

16. 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.

17.  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).

18. Boundaries
Go to Ch8 (8.2) Mountain Maker, Earth Shaker

19. Divergent Boundaries
Places where newly formed rocks pull the plates apart, like in the Mid-Atlantic Ridge, are called Divergent Boundaries.

20. Convergent boundaries
Places where plates push together, like in Japan, are called Convergent boundaries.

21. Transform Boundaries
Places where plates slide past each other are called Transform Boundaries.

22. 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.

23. Subduction Zone
The area where one plate is pulled under another is called a Subduction Zone.

24. 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.

25. Canadian scientists who have made a contribution to local, regional and global geology:
J. Tuzo Wilson
Joseph Tyrell
Harold Williams

26. 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.

27. Joseph Tyrell
Joseph Tyrell discovered dinosaur fossils in Alberta that proved that the local climate was warmer at an earlier time

28. Harold Williams
Harold Williams talked about the plate tectonic activity along the eastern edge of the North American continent.