Transcript Topic VI: The Dynamic Earth

Topic VI:
The Dynamic Earth
Earth’s Four Zones:
1.
Crust: the outside or surface—made up of
mostly igneous rock with a thin shell of
sedimentary rock on the outside
Crust types….
a.
b.
Oceanic Crust: only about 5 miles thin—
made up of basalt (dense)
Continental Crust: about 30 miles thick—
made up of granite (less dense)
2.
Mantle: the middle layer that the crust
“floats” on—divided into 3 parts:
a.
b.
c.
Rigid Mantle
Asthenosphere
Stiffer Mantle
**the Lithosphere is the crust AND rigid mantle
**the MOHO—boundary between the crust and mantle
3.
Outer Core: liquid nickel & iron
4.
Inner Core: solid because of high
pressure / made of nickel and iron
Why Nickel & Iron?.....

Meteorites!—more dense, sank to “center”
of young molten Earth
What happens the deeper you go in the Earth?

Density, temperature, pressure all
increase
Page 10
How do we know what Earth’s interior looks like?

Study Earthquake waves (like an ultrasound)
What does the heat from the core cause?

Continental Drift: the lithosphere (crust)
is made up of solid plates that move (plate
tectonics)
 Plates
move because of heat that rises
in the Asthenosphere due to density
differences—called convection
currents or cells
More Convection Currents….
Even More Convection Currents:

Plate Boundaries: areas on Earth where
two plates are interacting with each other
**this is
Where most
Volcanoes /
EQ’s / and
Mountains
Occur
Three Types of Plate Boundaries:
1.
Convergent: plates collide (subduction
zone—plate moves under another)
2.
Divergent: plates move apart
Page 10
3.
Transform: plates move side to side
USA

Hotspots: places in Earth’s crust with an
unusually high heat flow (Hawaii)
**plates move only a few centimeters per
year—about as fast as your fingernails
grow
Evidence of Plate Motion:
1.
Deformed (messed up) Rock Strata (layers)
**because of gravity, all sedimentary rocks
formed in horizontal layers (law of original
horizontality)
If not horizontal, the layers can be…
a.
Tilted: force pushes rock layers from 1
side
Force
b.
Folded: forces push on rock layers from
2 sides (rocks are not broken)
Force
Force
c.
Faulted: a break in the earth’s crust
where movement occurs
Force
Force
Williamsport, PA
2.
Displaced Fossils: marine fossils found
in rock layers several hundred feet above
sea level (uplift)
3.
Subsidence: sinking of rock layers
(fossils being found deep underground)
4.
Continents Fit together like a puzzle
5.
Rock layers and fossils may be
correlated (matched-up) across oceans
6.
Continuation of mountain chains from
continent to continent
7.
Evidence (fossils / rock) indicates that
the climate was much different (coal
found in Antarctica)
Coal forms in a tropical swamp
New York: Salt and Marine Fossils
Evaporated Ocean
8.
Sea Floor Spreading (Divergent Plate
Boundary)
Evidence of Sea-Floor Spreading:
a.
Radioactive Dating found that as rocks
get closer to the continents they get older
**more on this later
b.
Reversal of Magnetic Polarity: the
Earth’s magnetic poles switch from time
to time—this can be seen because of
iron in basaltic ocean rocks
**Iron (magnetic) in the liquid basalt line up
like compass needles (stays when it hardens)
Mid-Ocean Ridge
Cold
Hot
Cold
Old
Young
Old
Earthquakes

Earthquakes: a sudden shaking or
trembling of rock layers along a fault line
or plate boundary (the rock layers slip)
**energy is released and is transmitted by 2
types of waves
1.
2.
Primary or “P” waves (Compressional )
Secondary or “S” waves (Shear waves )

Seismic Stations: located around the world—
used to study earthquake waves.
 Seismographs:
device that records the
vibrations of earthquake waves
waves

P-waves: travel “phastest” so it arrives at
the seismic stations “phirst”

Can travel through solid rock & magma (can
travel through ALL Layers)

S-waves: travels slower so it arrives at
seismic stations second

Only travel through SOLIDS—all layers
EXCEPT LIQUID outer core and Solid Inner
Core
Origin Time (what time EQ began at
the epicenter)
Epicenter
Felt

Epicenter: point on the surface (city)
directly above the focus (in the interior
where the earthquake occurs)
**P & S waves travel
out in all directions
How is an earthquake’s epicenter located on a map?
1.
Get P and S wave arrival times from 3
different seismic stations
2.
Using the ESRT’s, find the distances from the
epicenter for each station
**The larger difference
between P and S wave
arrival times means that
the seismic station is farther
away from the epicenter
3.
Using the distances and a compass,
draw 3 circles
**Where the three
circles intersect the
epicenter is located
**as these P & S waves travel, they change speed
and bend (refract) as they enter different
substances and / or different densities
**this is how we know
what Earth’s interior
Looks like
**remember the
ultrasound?

Shadow Zone: a region on the Earth
where no P and S waves are recorded
(because of refraction & lack of s-waves)
Earthquakes in NY (rare)
**Remember
Lat / long
Earthquake Strength

Richter Magnitude Scale: measures the
amount of energy an earthquake releases
(uses seismographs)
**1 (little energy) 
10 (tremendous energy)
Strong
Weak

Mercalli Intensity Scale: based on what
damage people observe and shaking felt—
can be used for historical earthquakes
(newspaper articles)
Roman Numerals:
I (little)  XII (lots)

in the cases of both scales, the closer you are to the
epicenter, the more you will feel the shaking—meaning
the numbers will be higher the closer you are to the
quake
Does this make sense…..


The closer you are to the epicenter, both P &
S waves will be found at nearby seismic
stations
Stations on the other side of the world may or
may not pick up P & S waves
Earthquakes can cause:
a.
Tsunamis: seismic sea waves
(oceans)—can cause severe coastal
damage
b.
c.
d.
Landslides /
avalanches
Fires
Train / Car wrecks
Earthquake Emergency Planning
a.
b.
c.
Get away from windows, chimneys
Get under something strong (doorway)
Don’t try to get outside (last < 30 sec)

Volcanoes: mountain composed of
extrusive igneous rocks that can erupt
gases, lava, ash, and rocks onto Earth’s
surface
Volcanic Hazards
a.
Ash (buries everything)
b.
c.
Lava (usually moves slow—people
avoid)
Shooting, hot rocks (bombs)
d.
Mudslides (ash mixes with snow and dirt
from mountain tops)