2. Concept
It is a scientific theory that describes the large-
scale motions of Earth's lithosphere. The theory
builds on the concepts of continental drift,
developed during the first decades of the 20th
century.
3. How it works
The lithosphere is broken up into tectonic
plates. On Earth, there are seven or eight major
plates (depending on how they are defined) and
many minor plates. Where plates meet, their
relative motion determines the type of boundary.
Earthquakes, volcanic activity, mountain-
building, and oceanic trench formation occur
along these plate boundaries.
The outer layers of the Earth are divided into
lithosphere (outer) and asthenosphere (inner).
4. How do they move?
Tectonic plates are able to move because the
Earth's lithosphere has a higher strength and
lower density than the underlying asthenosphere.
Mechanically, the lithosphere is cooler and more
rigid, while the asthenosphere is hotter and flows
more easily. Therefore, in simpler terms:
The key principle of plate tectonics is that the
lithosphere exists as separate and
distinct tectonic plates, which ride on the fluid-like
asthenosphere.
5. Why do they move?
Plate tectonics is basically a kinematic phenomenon:
Earth scientists agree upon the observation and
deduction that the plates have moved one with
respect to the other, and debate and find agreements
on how and when. But still a major question remains
on what the motor behind this movement is; the
geodynamic mechanism, and here science diverges
in different theories.
One of the theories says: different forces generated
by the rotation of the globe and tidal forces of the Sun
and the Moon. The relative importance of each of
these factors is unclear, and is still subject to debate.
6. Who thought of this?
In 1912 the meteorologist Alfred
Wegener amply described what he
called continental drift.
Continental drift is the movement of the Earth’s
continents relative to each other.
Starting from the idea (also expressed by his
forerunners) that the present continents once
formed a single land mass (which was
called Pangea later on) that drifted apart, thus
releasing the continents from the Earth's mantle
and likening them to "icebergs" of low
density granite floating on a sea of denser basalt.
7. Formation and break-up of continents
The movement of plates has caused the formation
and break-up of continents over time, including
occasional formation of a supercontinent that
contains most or all of the continents. The
supercontinent Columbia or Nuna formed during a
period of 2,000 to 1,800 million years ago and broke
up about 1,500 to 1,300 million years ago.
This pieces later re-assembled into another
supercontinent called Pangaea; Pangaea broke up
into Laurasia (which became North America and
Eurasia) and Gondwana (which became the
remaining continents).
8. Plate Boundaries
The location where two plates meet is called
a plate boundary, and plate boundaries are
commonly associated with geological events
such as earthquakes and the creation of
topographic features such as mountains,
volcanoes, mid-ocean ridges, and oceanic
trenches. The majority of the world's active
volcanoes occur along plate boundaries, with the
Pacific Plate’s Ring of Fire being most active
and most widely known.
11. Divergent Boundaries
Divergent boundaries (Constructive) occur where two
plates slide apart from each other. Active zones of rifting
(such as Africa's East African Rift) is an example of
divergent boundaries.
12. Subduction
In geology, subduction is the process that takes
place at convergent boundaries by which one tectonic
plate moves under another tectonic plate, sinking into
the Earth's mantle, as the plates converge. These
regions of mantle downwellings are known as
"Subduction Zones". A subduction zone is an area
on Earth where two tectonic plates move towards one
another and one slides under the other.
Rates of subduction are typically measured in
centimeters per year, with the average rate of
convergence being approximately 2 to 8 centimeters
per year (about the rate a fingernail grows).
14. Effects
The strains caused by plate convergence in
subduction zones cause earthquakes.
Nine out of the ten largest earthquakes to occur
in the last 100 years were subduction zone
events. This includes the 1960 Great Chilean
Earthquake (which at 9.5 was the largest
earthquake ever recorded), the 2004 Indian
Ocean earthquake and tsunami, and the 2011
Tōhoku earthquake and tsunami.
15. Hot Spots
The places known
as hotspots or hot spots in
geology are volcanic regions
thought to be fed b underlying
mantle that is anomalously hot
compared with the mantle
elsewhere. They may be
on, near to, or far from
tectonic plate boundaries.
16. Hot Spots
Hawaii, Réunion, Yellowsto
ne, Galápagos,
and Iceland are some of
the most currently active
volcanic regions to which
the hypothesis is applied.
Pinnacle Rock, Galápagos Islands
17. Group Work
Get together in groups of five and research on the
following sites:
Hawaii, Réunion, Yellowstone, Galápagos, or Iceland.
First, look up what they have in common. Then you
may have a better idea of what you need to research
on.
You will have to prepare an oral presentation of five
minutes with multimedia.
Remember, it must all be related with GEOLOGY.
You have two weeks to have it ready.
Only the best and most outstanding presentation in
the class, will have a 20 as a final grade on the
project.
