
Layers – by composition
◦ Crust - Granite/Basalt
◦ Mantle - Peridotite/Gabbro
◦ Core
- Iron/ Nickel

Layers – by physical properties
◦
◦
◦
◦
Lithosphere - Solid/ rigid
Asthenosphere - Platic-like / silly putty
Outer Core - Liquid
Inner Core - Solid

Crust
◦ Continental crust
 Average rock density about
2.7 g/cm3
 Composition = Granitic
igneous rock

Crust
◦ Oceanic crust
 Density about 3.0 g/cm3
 Composition = Basaltic
igneous rock

Mantle
◦ Contains 82% of Earth’s
volume
◦ Upper portion has the
composition similar to
peridotite
◦ Two parts
 Asthenosphere -upper mantle
 Mesosphere -lower mantle

Core
◦ Larger than the planet
Mars
◦ Mostly iron with some
nickel
 Average density is nearly 11
g/cm3
◦ Two parts
 Outer core - liquid
 Inner core - solid due to
excess pressure

Core
◦ Responsible for
Earth’s magnetic
field
 Made of material that
conducts electricity
 Core is mobile

How do we know what is inside the
Earth??
??
??

Seismic waves
◦ P waves
• Travels through liquids as well as
solids
• In all materials, P waves travel
faster than do S waves
◦ S waves
• Cannot travel through liquids

Seismic waves
◦ Seismic waves refract (bend) as they pass from solid
to plastic-like to liquid material.
◦ P & S wave shadow zones created by this.



Researchers noted geographic fit of
continents, e.g. Africa and S. America
Seuss, 1885, proposed super continent by
studying fossils, rocks, mountains
Alfred Wegener - First proposed his
continental drift hypothesis in 1915
Wegener’s Hypothesis:



All land was joined together as one
Supercontinent called Pangaea which
began breaking apart about 200 million
years ago moving.
Pangaea Activity link
http://www.saskschools.ca/curr_content/
rbtboxes/mcrust/objects/pangea.html

Fit of the
continents


Fit of the
continents
Rock type &
structural
similarities



Fit of the
continents
Rock type &
structural
similarities
Fossil evidence
Fossils of Mesosaurus have been found on both
sides of the South Atlantic and nowhere else in the
world. Fossil remains of this and other organisms
on the continents of Africa and South America
appear to link these landmasses during the late
Paleozoic and early Mesozoic eras.




Fit of the
continents
Rock type &
structural
similarities
Fossil evidence
Past climate
evidence
New Technology adds new
evidence.

Proposed by Harry Hess in the late 1950s /
early 1960s
• New crust forms at ocean ridges
• Old crust destroyed at trenches
• Developed theory of sea floor spreading driven by
convection cells

Harry Hess’s Evidence:
Ocean floor is NOT flat!
• US Navy used SONAR to measure ocean
floor depth under Hess’s direction
• Found a Mountain Range in the middle of
the Atlantic
• Called it the
Mid-Atlantic-Ridge

Age of Sea Floor
• A – D represent drilling
sites on the ocean floor.
• Which samples had the
youngest rock?
B and C
• Which the oldest?
A and D
• Oldest rock on sea floor
only 200 m.y. (million years)
• Earth 4.6 b.y.


Earth's magnetic field
resembles that produced
by a large bar magnet.
Seafloor mapping in the
1950’s and 1960’s
showed Earth’s polarity
switched many times in
the past.
◦ Paleomagnetism = the study
of past polarity of Earth
As new basalt is
added to the
ocean floor at the
mid-ocean ridges,
it is magnetized
according to
Earth's existing
magnetic field.
Hence, it behaves
much like a tape
recorder as it
records each
reversal of the
planet's magnetic
field.

Hot spots
◦ Caused by rising plumes of mantle material
◦ Volcanoes can form over them (Hawaiian Island
chain)
◦ Most mantle plumes are long-lived structures and
at least some originate at great depth, perhaps at
the mantle-core boundary
+
+
+
=
Continental Drift
Sea-Floor Spreading
Paleomagnetism
Plate Tectonics
A New Theory



Earth’s lithosphere is broken up into plates
Hot, weak asthenosphere allows for plates to
move
Plates are in motion and continually changing
in shape and size
◦ Move very slowly 2 – 5 cm/yr
Evidence of Plate Boundaries
Evidence of Plate Boundaries
Evidence of Plate Boundaries

Plate boundaries
◦ All major interactions among individual plates occur
along their boundaries
◦ These interactions cause consequences such as:
 Earthquakes
 Volcanic eruptions

Plate boundaries
◦ 3 Types of plate boundaries
1. Divergent plate boundaries
2. Convergent plate boundaries
3. Transform fault boundaries

Divergent Plate boundaries
◦ Most are located along the crests of oceanic ridges
 Mid-Atlantic-Ridge (MAR)
◦ Also continental rifts
 Great African Rift Valley
◦ A few are on land
 Great African Rift Valley
 Iceland
Ex: Yellowstone National Park
Ex: Great Rift Valley
Ex: Red Sea
Ex: Atlantic Ocean

Convergent plate boundaries
◦ Where two plates collide
◦ 3 Types
1. Oceanic-Continental convergence
2. Oceanic-oceanic convergence
3. Continental-continental convergence

Transform fault boundaries
◦ Plates slide past one another
◦ No new lithosphere is created or destroyed
◦ Transform faults
 Most join two segments of a mid-ocean ridge as parts
of prominent linear breaks in the oceanic crust known
as fracture zones