The Earth's crust is divided into tectonic plates that are in constant motion due to convection currents in the upper mantle. There are three types of plate boundaries: divergent where plates move apart and new crust is formed, convergent where plates collide and can cause mountain building, and transform where plates slide past each other. Alfred Wegener first proposed the theory of continental drift in 1912, and the modern theory of plate tectonics explains how plate motions and interactions have shaped Earth's surface over geological time through subduction, volcanism, earthquakes and mountain formation.
2. The Earth’s Crust and Plate
Tectonics
The Earth’s Crust
This is where we live!
The Earth’s crust is
made of:
Continental Crust
- thick (10-70km)
- buoyant (less
dense than
oceanic crust)
- mostly old
Oceanic Crust
- thin (~7 km)
- dense (sinks
under
continental
crust)
- young
3. If you look at a map of the world, you may notice that some of the
continents could fit together like pieces of a puzzle…
5. Plate Tectonics
• The Earth’s crust is divided into many major
plates which are moved in various
directions.
• This plate motion causes them to collide,
pull apart, or scrape against each other.
• Each type of interaction causes a
characteristic set of Earth structures or
“tectonic” features.
• The word, tectonic, refers to the
deformation of the crust as a consequence
of plate interaction.
6. What are tectonic plates made of?
Plates are made of rigid lithosphere.
The lithosphere is made
up of the crust and the
upper part of the mantle.
7. Pangaea
Alfred Wegener proposed the Continental Drift Hypothesis in
1912, that stated Earth’s continents were once joined in a
single landmass and gradually moved or drifted apart.
8. Theory of Plate Tectonics
Fossils, Climate, & Geology
• http://library.thinkquest.org/17701/high/pangaea/
• http://www.pbslearningmedia.org/resource/ess05.sci.ess.earthsys.plateintro/plate-tectonic
9. Evidence from the Sea Floor
http://library.thinkquest.org/17457/platetectonics/4.php
10. Three types of plate boundary
Divergent
Convergent
Transform
14. Convergent Boundaries
• 2 plates that are pushing together
• There are three types of convergent
plate boundaries
– Continent-continent collision
– Continent-oceanic crust collision
– Ocean-ocean collision
18. Oceanic-Oceanic Plate
Subduction
• When two oceanic plates
collide, one runs over the other
which causes it to sink into the
mantle forming a subduction
zone.
• Island arcs form
• The subducting plate is bent
downward to form a very deep
depression in the ocean floor
called a deep ocean trench.
• The worlds deepest parts of the
ocean are found along trenches.
– E.g. The Mariana Trench is
11 km deep!
20. Magnetic Reversal• After molten lava emerges from a volcano, it solidifies to a
rock. In most cases it is a black rock known as basalt, which
is faintly magnetic (iron)
• Its magnetization is permanently fixed like tiny compass
needles pointing north & south.
• Instruments can measure the magnetization of basalt.
• Surprisingly, this procedure suggested that times existed
when the magnetization had the opposite direction from
today's. All sorts of explanation were proposed, but in the
end the only one which passed all tests was that in the
distant past, indeed, the magnetic polarity of the Earth was
sometimes reversed.
