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Dynamic Crust
Continental Drift - The Theory
Theory that all of the continents were once joined together in a single
landmass and have since drifted apart.
Pangaea
“All Earth” or name given to the super continent that existed
200 million years ago.
Alfred Wegener, 1915
• German geologist and meteorologist
• Proposed the theory of continental drift
• Hypothesized a gigantic super continent
Continental Drift - Evidence
1. Similarities in the shape of Africa’s west coast
and South America’s east coast.
Continental Drift - Evidence
2. Fossil remains of the Mesosaurus were found in
South America and South Africa.
Continental Drift - Evidence
3. Fossil remains of the Glossopteris were found
throughout India, South America, Africa, and
Antarctica.
Crustal Activity
• Plate Tectonics - the study of the formation and movements
of plates
• Plates - section of the lithosphere that moves around
• Lithosphere - Earth’s solid outer crust and rigid mantle
• Asthenosphere - partially melted layer that flows slowly
and is located below the lithosphere (plastic)
Crustal Activity
• Earth’s surface consists of a
dozen major plates and
some minor ones.
• The plates are moving at
rates close to 10 cm/year
• Convection Currents - driving force of plate movement
• Magma heats up causing it to expand and rise
• Magma cools down causing it to contract and sink
• The plates are moving on top of the asthenosphere due to
density differences.
• The idea of continental drift had been around since the
early 1900’s, but lacked enough scientific evidence to
support the theory.
• New advancements after World War II help provide the
evidences needed to validate the Theory of Plate Tectonics.
Crustal Activity - Earthquake Evidence
• Scientist noticed that earthquakes do not occur at
random location, but run throughout the world along
isolated belts
• When plotted on a map they outline the plate
boundaries
Crustal Activity – Volcanic Evidence
• Occurs at plate boundaries where plates are
interacting
• Ring of Fire - isolated belt around the Pacific Ocean
where 90% of the world’s volcanoes exist
Crustal Activity – Rock Evidence
• Sedimentary deposits and igneous lava flows are usually placed
down in horizontal layers.
• Sometimes movement along boundaries causes these layer to tilt or
fold
Crustal Activity – Mountain Evidence
• As plates collide they sometimes are pushed upward.
• Fossilized marine organisms can be found at these high altitudes in
the rock.
Crustal Boundaries
• Tectonic plates are constantly moving and interacting
• As they move across the asthenosphere and form
plate boundaries they interact in various ways
• The types of plate boundaries are:
• Divergent
• Transform
• Convergent
Crustal Boundaries
Crustal Boundaries
• Convergent Boundary - boundary where two
lithospheric plates are coming together.
• Example: the India Plate pushing upward into Eurasian
Plate and creating the Himalayan Mountains
Crustal Boundaries
• Convergent - Subduction while plates are moving together, one
plate is pushed below another and consumed in the mantle
• Example: the Nazca Plate being consumed under the South
American Plate.
Crustal Boundaries
• Three Types of Convergent Boundaries:
• Ocean / Ocean Boundary
• Ocean / Continental Boundary
• Continental / Continental Boundary
Crustal Boundaries
• Divergent Boundary - boundary where two plates are moving apart
• Example: the Mid Atlantic Ridge
Crustal Boundaries
• Sea Floor Spreading the process where ocean floor is extended when two
plates move apart
• Mid Ocean Ridge underwater mountain range created from a divergent plate
boundary
Crustal Boundaries
• Mid Atlantic Ridge a mid ocean ridge that runs the length of the Atlantic Ocean
• Separates the North and South American Plates from the Eurasian and African Plates
Crustal Boundaries
• Rift Valley - long narrow valley that runs the entire length of a mid
ocean ridge system
Crustal Boundaries
• Scientists dragged a magnetometer across the ocean floor and discovered a
unique magnetic pattern where stripes of normal and reversed polarity parallel
the mid ocean ridge flipping every 200,000 to 300,000 years the last one
was781,000 years ago.
Crustal Boundaries
• Rock samples
of the deep
ocean floor
show that
basaltic
oceanic crust
becomes
progressively
younger as you
approach the
mid ocean
ridge
Crustal Boundaries
• Transform Boundary - boundary where two lithospheric plates are sliding
past one another
• Example: the San Andreas Fault is 800 km long and runs throughout
California
Earth’s Interior
• Earth’s interior structures are known through the
study of seismic waves
• Seismic waves refract, reflect, change velocity, and
are absorbed depending on the material they are
transmitted through.
Earth’s Interior
•Lithosphere - Earth’s crust and outer most layer
•Continental Crust - thickest (100 km) and least
3
dense 2.7 g/cm part of the lithosphere
•Oceanic Crust - thinnest (2-3 km) and most
dense part of the lithosphere 3.0 g/cm3
Earth’s Interior
• MOHO - thin interface separating the lithosphere from
the asthenosphere
• Asthenosphere - a partially melted layer that allows
for parts of the lithosphere to move
• Discovery: a decrease in velocity from earthquake
waves
Earth’s Interior
• Mantle - thickest part of Earth (80%) and is between the crust and the outer core
Earth’s Interior
• Outer Core - liquid layer of Earth’s interior between the mantles and the inner
core
• Discovery: the absorption and refraction of earthquake waves
Earth’s Interior
• Inner Core - the solid inner most zone of Earth’s core composed of iron (Fe)
and nickel (Ni)
• Discovery: an increase in velocity from earthquake waves
Earthquakes
•Earthquake - a natural shaking of the
lithosphere caused by a release of energy
stored in rocks
•Most earthquakes are caused by a movement
along a fault where potential energy is given o"
as a seismic wave
• Epicenter - on Earth’s surface directly above the focus
• Focus - point inside the Earth where the earthquake
originates
Earthquakes
• Seismometer - An instrument used to measure and record movements in the
ground
Earthquakes
Seismogram - record of the seismometer
Earthquakes
• Mercalli Scale - scale that
measures the intensity of an
earthquake based on the effects
to Earth’s surface, humans,
objects in nature, and other man
made structures.
Earthquakes
• The values will differ based on the distance from the
epicenter:
•Highest intensities are closer
•Lower intensities are farther away
Earthquakes
Richter Scale – logarithmic scale that measures the
amount of energy released during an earthquake
Magnitude - a number to quantify the amount of
seismic energy released from an earthquake
Earthquakes
• The Richter Scale’s magnitude is determined from the
following measurement:
•Seismogram’s amplitude of waves
•Distances from other seismographs
•Epicenter distance
Earthquakes
• Primary Wave (P – wave)
•are the fastest waves
• Travels through solids, liquids, and gases
• Compressional - particles travel in the
direction of wave movement
Earthquakes
•Secondary Wave (S – waves)
•are the slower wave
• Travels through solids only
• Shear particles travel in right angles to
the direction of wave movement
Earthquakes
•Seismic
waves
radiate away
from the
focus
Earthquakes
• Shadow Zone area in which
seismic waves
are not
detected due to
the liquid outer
core
Earthquakes
• P - waves are refracted when they reach the liquid
outer core
• S - waves are absorbed when they reach the outer
core and are not transmitted through to the other side
Earthquakes
• Epicenters are
located using
the velocity
differences
between the pwave and swave
Earthquakes
• Since p-waves
travel faster then
s-waves, as your
distance
increases from
the earthquake’s
epicenter the
arrival time
between the two
waves will be
greater
Earthquakes
Distance to the epicenter is
determined by comparing the
arrival times and the E.S.R.T.
Earthquakes
To find the epicenter location you need to triangulate a
position using
three different seismometer stations.
This is called TRIANGULATION.