Download Continental Drift and Plate Tectonics

Layers of the Earth - Students’ Notes
Geology – comes from two Greek roots: ‘geo’ means earth and ‘logos’ means the
study of. So geology is the study of earth. Scientists use seismic waves to study the
layers of the Earth.
Earth’s shape is nearly a sphere, with a slight flattening at the poles. The ocean
covers 71% of the earth’s surface. Seven major continents make up the rest of the
surface. Name the continents: Australia, Asia, Africa, Antarctica, Europe, North
America and South America.
I.
Four Layers – they get hotter as they go deeper
A.
Crust: outermost layer - two types
1.
Continental Crust is formed over the continents. The thickest parts are under
mountain ranges.
2.
Oceanic Crust is found beneath the ocean floor and is much thinner than the
continental crust.
B.
Mantle: accounts for more than 80% of the volume of Earth. It is divided into
zones of different densities. The upper mantle is less dense and the lower mantle is
more dense.
1.
Lithosphere – is made up of the crust and the upper most solid portion
of the mantle.
C.
Core: is the very center of the earth. It is made up of mostly iron (Fe) and
nickel (Ni). It is divided into two parts: outer core, inner core
1.
Outer Core: is molten liquid
2.
Inner Core: is solid. This is the hottest layer.
Continental Drift and Plate Tectonics
good resource http://pubs.usgs.gov/gip/dynamic/understanding.html#anchor15039288
I.
Continental Drift
A. Proposed by Alfred Wegener in 1912
1. Theory that Earth’s continents were once joined in a large landmass
that broke apart. The continents drifted to their current locations.
(they drift a few centimeters each year)
2. Named the giant landmass Pangaea- Greek word that means “all
Earth”
3. Fossils and rock formations found on the different continents
support his theory.
4. Theory was not readily accepted because he couldn’t explain how it
happened.
II.
Plate Tectonics Theory A. The theory is that the Earth is divided into lithospheric or tectonic plates
that move about the Earth (like slabs of ice on a lake) “tekton” is a Greek
word that means “to build”. They move at a rate of 1-10 cm per year.
B. Lithosphere - (lithos is Greek root for rock or stone)
1. Outermost layer of Earth’s surface
2. Includes the crust and the rigid portion of the upper mantle
3. Composed of tectonic or lithospheric plates (7 major platescorresponding w/ the continents and 7 minor plates)
4. Part of the Earth where all geological events take place: earthquakes,
volcanoes, mountain formation, tsunamis, geysers, erosion, and rock
formation
III.
Convection Current
A. Hypothesis to explain how plates move
B. Asthenosphere – this is the upper part of the mantle that is partially molten
in places. Convection current takes place in this layer.
C. Hot molten material in the mantle becomes less dense and rises
D. Material nearer to Earth’s surface spreads out, cools and becomes denser.
Then it sinks below the hotter, less dense material.
E. Uneven heating causes material in the mantle to constantly and slowly rise
and fall, resulting in convection current.
F. As the currents move molten material sideways, large portions of crust
(plates) “ride” on top across the Earth’s surface.
IV.
Plate Boundaries –
A. The place where the edges of tectonic plates meet.
B. Types of boundaries depend on whether the plates forming them are
moving toward each other, separating or sliding past each other.
C. Geologic events happen along these different boundaries
D. Three Different BoundaryTypes:
i. Convergent Boundary - Forms where plates collide. 3 possibilities:
1. Continental Plate to Continental Plate: the two plates just fold
together and keep pushing on each other. Mountains are
formed.
(example: Himalayas)
2. Continental Plate to Ocean Plate: two plates come together
and the oceanic plate slides underneath the continental plate.
The lower one starts being melted back into magma. This is
called subduction. (example: Andes Mtns.)This molten
material, which is under great pressure can escape through
weak spots in the Earth’s crust. What can happen? Erupting
volcanoes.
3. Ocean Plate to Ocean Plate: two plates come together and one
slides under the other (subduction) When this happens in the
middle of the ocean, strings of volcanic islands are formed.
(example: Hawaii)
ii. Divergent Boundary
1. Forms when 2 plates diverge, or move away from each other.
This usually happens on the ocean floor.
2. A space is created where magma comes through, forming new
crust. The creation of new ocean floor is called seafloor
spreading.
3. They build under sea mountain ranges (example: Mid-Atlantic
Ridge which is longest mountain range in world)
iii. Transform Boundary (lateral boundary)
1. Forms when two plates slide past each other in opposite
directions, without creating or destroying crust.
2. Causes earthquakes as boundaries grind against each other.
(Example: San Andreas Fault)
3. Called seismic zones
4. Can also create mountains, valleys and volcanoes.
Ring of Fire
Ring shaped belt of volcanic and earthquake activity surrounding the
Pacific Ocean. This happens because there are so many plates
either converging, diverging, or transforming along the edges of the
Pacific Plate. It is usually the dense oceanic crust that is moving
under the less dense continental plates.