Transcript Earth Structure

Marine Science Unit 3
Earth Structure
iceagenow.com
Layers of the Earth Objectives:
• Identify the layers of the Earth in the order in
which they occur.
• Know general characteristics of each layer
(thickness, temperature, elemental
composition)
• What is isostatic equilibrium?
• What is bouyancy?
Layers of the Earth
•
•
•
•
Inner Core
Outer Core
Mantle
Crust
myschoolhouse.com
The Core
• Made up of iron (90%) and nickel with some
silicon, sulfur, and other heavy elements
• Temperature of 5,500oC (9032oF)
• The total core (inner and outer together) have
an estimated radius of 3470km
• 31.5% of the Earth’s mass and 16% of the
Earth’s volume
Inner Core
• Theorized to be solid
due to intense pressure
• New evidence suggests
that the inner core may
get as hot as 6,600oC at
its center – hotter than
the surface of the sun
news.sciencemag.org
Outer Core
• Less pressure than inner
core it is theorized to be
a dense liquid
• Can have thermal plumes
colorado.edu
Mantle
• Contains silicon and
oxygen with some iron
and magnesium
• Estimated to be about
2,900km thick
• Made up of the upper
and lower mantle
• 68% of the Earth’s mass
and 83% of the Earth’s
volume
volcano.oregonstate.edu
Mantle
• Upper Mantle
• Lower Mantle
– Made up of two layers
– 1. Asthenosphere
(asthenes=weak): The layer
that is partially melted slowly
flowing below the
lithosphere extending to a
depth of 350-650km
– 2. Lithosphere (lithos=rock):
Earth’s cool rigid outer layer
that is 100-200km thick
– Extends to the core
– More dense and flows
more slowly
• Made up of the rigid solid
upper portion of the mantel
and the crust
ksl.com
Crust
• Thin solid outermost layer
of the Earth
• Relatively cool temperature
• 0.4% of Earth’s mass and 1%
of Earth’s volume
• Composed of oxygen,
silicon, magnesium, and
iron
• Oceanic Crust
– Thin and made up of mostly
basalt (heavy dark colored
rock)
• Continental Crust
– Thicker and made up of
mostly granite (light-colored
rock)
How does the crust float on the mantle?
• Isostatic Equilibrium: Balance
between the weight of the crust and
the buoyancy provided by the
mantle
– As material adds to the oceanic
crust or leaves the continental crust
the balance becomes disrupted
– Isostatic Rebound: The additional
weight causes the crust to move
down while the removal of material
will cause the crust to move
upwards
– To restore equilibrium landmasses
rise or sink along a weak area called
a fault
– One theory of what causes
earthquakes is when landmasses on
either side of an involved fault do
not move together
cliffsnotes.com
Buoyancy
• Archimedes’ Principle of Buoyancy: An object
immersed in a fluid (gas or liquid) is buoyed
up by a force equal to the weight of the fluid
displaced – an object that weighs less than the
fluid it displaces will float
– If the weight of the crust changes, the landmass
must rise or sink to compensate
http://www.pbs.org/wgbh/nova/lasalle/buoybasics.html
Journey to the Center
of the Earth Activity
• http://www.youtube.com/watch?v=bKVzVhqP
Rf4
Continental Drift Objectives:
• Explain the theory of Continental Drift.
• Who developed the theory of Continental
Drift?
• Explain the different types of evidence that
support the theory of Continental Drift.
Theory of Continental Drift
• 1912 Alfred Wegener
proposes that the
continents were once a
single landmass that
drifted apart (and are still
doing so)
• Pangaea (pan=all;
gaea=ocean) “super
continent”
• Pathalassa (thalassa=the
sea) single large ocean
geo.tcu.edu
Tectonic Jigsaw Activities 1 & 2
Compare the Pangaea you made in
Activity 2 to the “real” Pangaea
Continental Drift
Evidence for Continental Arguments against
drift:
continental drift:
• Shape of Continents
• Distribution of minerals
and fossil fuels
• Distribution of plant and
animal fossils
• Wegener couldn’t explain
how the continents
drifted
– Plate tectonics now provide
an explanation for this
• Jigsaw puzzle had gaps
– Including the continental
shelf fills in the gaps
*Wegener disappeared on an expedition to Greenland before his theory
became widely accepted…
Evidence for Continental Drift
• 1600’s - People notice
the shape of continents
fit together like a jigsaw
puzzle
• Mountain Range
Distribution
• http://dynamicearthass
essmenttask.blogspot.c
om/
rhnet.org
Evidence for Continental Drift
• Distribution of coal
• Salt deposits
– Coal forms from remains of
plants and animals in
swampy climates… coal is
present in Antartica where
there are currently no
swamps
– Salt deposits hundreds of
millions of years old are
found in locations where
salt deposits don’t form
• Limestone formation
– Limestone forms from the
remains of coral reefs
– Limestone has been found
in the north-central United
states (where there is no
sea water and is too far
north to support coral reef
growth)
http://dynamicearthassessmenttask.blogspot.com/
Evidence for Continental Drift
• Distribution of animal
fossils
– Ex. Lystrosaurus : bearlike extinct animal
– Ex. Mesosaurus: Extinct
aquatic reptile
– Led scientists to
conclude that 200 mill
yrs ago Pangaea split
into to continents
• Lower - Gondwanaland
• Upper-Laurasia
en.wikipedia.org
Evidence for Continental Drift
• Distribution of plant
fossils
– 1855 Edward Suess found
fossils of Glossopteris fern
in South America, Africa,
Australia, India, and
Antartica
– The seeds of this plant are
too fragile to travel by sea
and are too heavy to travel
by wind… so, how did they
get to so many different
places?
suu.edu
Invention of Sonar
• Detects objects under water by
transmitting a sound and
receiving an echo
• SONAR is an acronym that stands
for SOund Navigation and
Ranging
• Invented around the same time
that Wegener proposed the
theory of continental drift and
partly in response to the wreck of
the Titanic
• Scientists almost immediately
began using sonar technology to
map the ocean floor
– German Meteor expedition
mapped the contours and depths
of the South Atlantic in 1925
oscilatii2011.wikispaces.com
Plate Tectonics Objectives:
• What is the Theory of Plate Tectonics?
• Explain the difference between convergent,
divergent, and transform boundaries.
• What is the Hot Spot Theory and how does it
support the theory of Plate tectonics?
• Explain plate movement.
Theory of Plate Tectonics
• Unifies Seafloor spreading and
continental drift theories
• Theory of Plate Tectonics:
• The Earth’s lithosphere
consists of more than a dozen
separate plates
– Plates are rigid and float on the
lithosphere
– Some plates are entirely ocean
crust, some are entirely
continental crust, and other
plates are a combination
– Plates move a few centimeters
a year because of the
movement of magma beneath
them
vulcan.wr.usgs.gov
Plate Boundaries
• Plate Boundaries =
Where Plates Meet
• 3 possible motions
when plates meet:
– Spreading Apart
(Divergent Boundary)
– Pushing Together
( Convergent Boundary)
– Passing Side-by-Side
(Transform Boundary)
canarygeog.canaryzoo.com
Divergent Boundaries
• Two plates are moving apart
• The crust pulls apart and forms • http://geology.com/nst
valleys
a/divergent-boundary• Mid-Ocean Ridges and rift
oceanic.gif
valleys mark divergent
boundaries
• Magma from the athenosphere
flows up through the rift valley
creating new crust and
widening the seafloor
• Volcanic activity at divergent
boundaries can build mountains
higher than sea level forming
cotf.edu
new islands
– So, they are also known as
constructive boundaries
Convergent Boundaries
• 3 Types:
• Two plates are pushed
– Oceanic plate colliding with
together/colliding
oceanic plate
• AKA destructive boundaries
• One plate sinks beneath the other
• Can cause chain of volcanic islands
to form
– Oceanic plate colliding with
continental plate
• Oceanic plate is subducted
underneath the continental plate
and a trench forms
• Can cause volcanic mountain range
to form or earthquakes
cotf.edu
– Continental plate colliding with
continental plate
• Mountains form as the crust folds
Transform Boundary
• Two plates slide past each other
• Earthquakes are common as rocks move when
the plates slide
 Ex. San Andreas fault in California is the boundary between
the Pacific Plate moving north and the N. American Plate
moving south
gweaver.net
cotf.edu
Comparing the 3 Types
of Plate Boundaries
Hot Spot Theory
• 1963 – J. Tuzo Wilson observed that some volcanoes
exist far from plate boundaries
– He theorized that hot spots are small melting areas within
the mantel where thermal plumes cause magma columns
to push up through the crust (forming volcanoes)
•Hot spots can occur at fault lines
although most form far from plate
boundaries
Ex. Yellowstone
•Hot spots do not move with tectonic
plates, so volcanic areas change on the
plate as it moves
-This can result in a line or chain of
volcanic islands
pubs.usgs.gov
windows2universe.org
Plate Movement
• Primary force driving plate
movement = convection
– Convection: Vertical
circulation pattern in a gas or
liquid caused by hot materials
rising and cold materials
sinking
• This occurs in the mantel of
the Earth when warm
molten rock rises and cool
magma sinks and creates a
current that moves plates
• Secondary driving force
comes from seafloor
spreading
– As new seafloor forms, the
plates tend to slide away
from the elevated midocean ridges
– The leading oldest oceanic
plate tends to be dense
and thick and may
subduct/sink down
Mountain Maker Earth Shaker…
• http://www.pbs.org/wg
bh/aso/tryit/tectonics/#
Ocean Floor Features Objectives:
• What are mid-ocean ridges, rift valleys, and
trenches?
• What is the theory of seafloor spreading?
• What are three forms of evidence that
support the theory of seafloor spreading?
Physical Features of the Seafloor
• Continental Shelf – part of the continent that extends into ocean about
200km and is really part of the continent even though it is under water.
• Continental Slope – the steep slope at edge of the continental shelf that
drops off sharply
• Ocean Basins:
– Ridges – underwater mountain trains
– Trenches
– Abyssal Plain - flat plain that extends seaward from the base of the
continental slope
– Abyssal Hill - hills less than 1000m high on the abyssal plain (most are
volcanic in nature )
– Volcanic Islands
– Seamounts - Steep sided volcanoes on abyssal plain rising abruptly and
sometimes breaking the surface to become islands
– Guyots – Submerged flat-topped seamounts
– Atolls - When a seamount disappears below the surface and the coral reef
is left as a ring
visual.merriam-webster.com
legacy.mos.org
The Theory of Seafloor Spreading
• In the 1960’s geologists Harry
Hess and Robert Dietz
hypothesize that the seafloor is
in a constant state of creation
and destruction
• New crust emerges as magma
from the asthenosphere pushes
up through the rift and solidifies
into new crust. This new crust
pushes the old crust away from
the ridge.
• As this theory became accepted,
other scientists hypothesized
that old sea floor subsides or
sinks at trenches as it is drawn
downward by gravity and inertia
(eventually it reaches the
athenosphere and melts into
magma again)
• Is estimated to occur at about
the same rate at which your
fingernails grow.
• http://www.suu.edu/faculty/c
olberg/hazards/platetectonics
/30_SeaFloor.html
mail.colonial.net
3 Forms of Evidence
of Seafloor Spreading
1. Ocean Bottom
Sediment Samples
– Cores samples from
drilling showed that
sediment layers were
thin or absent at ridges
and thicker away from
the ridges – they found
the thickest layers near
continents
2. Radiometric Dating
– Used to determine the
age of rocks
– Using this method,
scientists have found
seafloor rock to be much
younger than
continental rock and
younger rocks near
ridges and older rocks
farther away.
Drilling Core Samples
of Ocean Sediments
oceanexplorer.noaa.gov
news.rutgers.edu
Radiometric Dating of Seafloor
ic.ucsc.edu
3 Forms of Evidence
of Seafloor Spreading
• 3. Magnetometer
– Magnetometer:
instrument that measures
the polar orientation and
magnetism of minerals
– Symmetrical patterns in
basalt (sea rock) show
that seafloor on either
side of the mid-ocean
ridges mirror each other’s
polar orientation
tulane.edu
Seafloor Spreading Activity
Sediments in the Sea Objectives:
• What techniques do
scientists use to study
ocean sediments?
• How do scientists use
ocean sediments to
study the past?
• How are sediments
classified by size?
• How are sediments
classified by origin?
• Explain the erosion and
deposition of ocean
sediments.
• How does the rate of
continental shelf
sedimentation compare
to the rate of ocean
sedimentation?
Marine Sediment
• Sediment: Organic and
inorganic particles
accumulated together
in a loose, consolidated
form
• Origins of sediment:
–
–
–
–
–
–
Weathering
Erosion
Hard-shelled organisms
Chemical processes
Volcanic Activity
Outerspace
soest.hawaii.edu
Why should we study marine
sediments?
• They are important to
many Earth cycles:
– Carbon
– Nitrogen
– Phosphorous
• They play a principle role
in plate tectonics as the
“crust”
• Scientists use them to
understand the Earth’s
past:
– Climate
– Ocean circulation patterns
– Biological development
• Deep within ocean
sediments we find natural
resources like:
– Coal
– Oil
– Natural gas
terradaily.com
USGS Sediments PodCast
• http://www.youtube.co
m/watch?v=X2F2XNns5
X4
Studying Sedimentation
• Stratigraphy: the study
of sediment layers
– Scientists look for clues
like rock composition,
microfossils, deposition
pattterns, and use them
to draw conclusions
about the past.
scientificamerican.com
Studying Sedimentation
• Paleoceanography:
Study of prehistoric
oceans
nps.gov
– Study chemical ratios
and radioactive isotopes
found in microfossils to
obtain evidence about
prehistoric ocean
conditions
preachrr.wordpress.com
Types of Sediments
• Two most common ways to study sediments in by
their:
– Origin (where they came from)
– Size
• 4 Origin Categories:
–
–
–
–
Lithogenous
Biogenous
Hydrogenous
Cosmogenous
• Size is classified by “grain”
size (or the diameter of
individual particles)
– Wentworth Scale
Classifying Sediments by Size
WENTWORTH SCALE
Classification
Grain Diameter
Example
Clay
Smaller than 0.004 mm
Talc or fine powder
Silt
0.004 mm - .0625 mm
Powder
Sand
0.0625 mm – 2 mm
Sugar crystals
Granule
2 mm – 4 mm
Aquarium gravel
Pebble
4 mm – 64 mm
Grape
Cobbler
64 mm – 256 mm
Cobblestone
Boulder
256 mm and larger
Brick or larger
Classifying Sediments by Size
• Currents and waves tend
to distribute sediments by
size
– The smaller a particle the
more easily it is moved by
the motion of the water
– Heavier particles require
more energy to move and
therefore don’t travel as
far as fine particles
• Generally larger, heavier
particles settle first…
lighter, smaller particles
take longer to settle
• Erosion: Process by which
sediments are
removed/transported
– Often by weathering, wind,
human interaction
• Deposition: Process by
which sediments, soil,
and rocks is added to a
landform or land mass
Lithogenous Sediments
• Come from the land
•
•
•
•
•
Greek lithos=stone
Greek generare=produce
AKA terrigenous sediments
Most abundant sediment by volume
Results primarily from erosion by wind,
water, and ice carrying rock and minerals
into the sea or from landslides or
volcanic eruptions
• Majority of lithogenous sediments are
near continents and islands
• Quartz (from granite) is the most
common mineral in lithogenous
sediments because it is hard and doesn’t
break down
• Feldspar (also from granite) breaks down
to form clay which is another common
lithogenous sediment – although clay is
often found farther from shore
• Rivers carry up to 15 bill metric
tons of lithogenous sediments
into the ocean annually
• 100 million metric tons of
lithogenous sediments transfer
from land to sea as find dust and
volcanic ash
newark.osu.edu
Hydrogenous Sediments
• Nodules: Hydrogenous
• From chemical
thought to be
reactions in seawater sediments
produced by the some of
• Greek hydro=water
• Chemical reactions cause
minerals to come out of
solution and form
particulates that settle on
the bottom of the ocean
• Accounts for less than 1%
of all sea floor sediments
• Found among biogenous
and/or lithogenous
sediments
the slowest chemical
reactions in nature…
many nodules are more
than 10 mill years old
– Ferromanganese Nodules:
Consist of iron,
magnesium, and small
amounts of cobalt, copper,
chromium, molybdenum,
and zinc
– Phosphorite Nodules:
Consist of phosphorite and
other trace minerals
Cosmogenous Sediments
• From outerspace
• Greek kosmos=space
• Primarily made up of
cosmic dust
– Cosmic Dust: Small
particles the size of sand or
smaller
– Thought to result from
collisions between objects
in space like asteroids and
comets
• Least abundant sediment
and make up no more
than a few parts per
million of marine
sediment
• 15,000 to 30,000 metric
tons of material from
space reaches the Earth’s
surface per year
– Microtektites: glass
particles that form when a
large meteorite impacts
Earth
Biogenous Sediment
• Come from organisms
• Biogenous sediments cover the
largest area of the sea floor
• Greek bios=life
• Most common in the deep
• Particles in this sediment come
ocean
from shell and hard skeletons
• Ooze: Deep ocean sediment
– Plankton obtain siliceous and
that consists of 30% or more
calcareous from the sea water for
biogenous sediment
form shells/skeletons which later
settle as sediment when the
organisms die
– Large organisms shells and hard
corals also contribute to this
sediment
• Under the right conditions …
they can form crude oil and
natural gas
– Accumulates slowly 1 to 6 cm per
thousand years
– Calcareous Oozes : Composed of
plankton remains with calcium
carbonate shells
– Siliceous Ooze: Composed of
plankton remains with silica
skeletons
Continental Shelf Sediments
• Continental Shelf: Located in
relatively shallow water and
near land
• Mixture of both lithogenous
and biogenous sediments
• Tides, waves, and currents
control continental shelf
sedimentation
– Surf and waves carry small
particles out to sea which keeps
most beaches sandy rather than
muddy
– Because waves and tides have less
effect in deep water, mud is
present off shore
• Sedimentation rates on the
continental shelf vary by region
• Sedimentation is more rapid on
the continental shelf than in the
deep ocean
• Continental sediments can
affect the deep ocean with
“avalanches” called turbidity
currents
– Thick muddy fluid rushes down
from the continental shelf into the
deep ocean forming turbidites
Deep Ocean Sediments
• High in biogenous material (from planktonic organisms)
• Clay and other lithogenous material cover about 38% of the deep
ocean floor
– Their small size allows currents to carry them farther
– Forms fine brown, olive, and red clay
• Made up of 30% biogenous sediment known as ooze
– Accumulates slowly 1 to 6 cm per thousand years
• The Atlantic Ocean has twice the sediment that the Pacific Ocean
has
Distribution of Marine Sediments
iupui.edu
Carbonate Compensation Depth
• The planktonic organisms
that leave behind
calcarous tests (skeletons)
die everywhere in the
ocean yet calcareous ooze
is only fond in the deep
ocean… why?
• Calcium carbonate depth
varies by region due to
temperature and water
chemistry
• Seawater contains carbon
dioxide and is more acidic
below 3,000 meters
which makes calcium
carbonate more soluble in
seawater
– It also more soluble in the
lower temperature of the
deep water
– At a certain point, calcium
carbonate dissolves as fast
as it forms= carbonate
compensation depth
Sediments as Economic Resources
• 1/3 of the world’s crude
petroleum and ¼ of the
world’s natural gas come
from sedimentary
deposits on the
continental shelf
• Many geological
oceanographers work in
the petroleum and gas
industry
• Other important
sediment resources
include:
– Evaporates like salt,
gypsum, calcium carbonate
(which are hydrogenous
sediments)
– Metal sulfide
– Dissolved minerals
– Sand and gravel (for
construction
– Diatomaceous earth –
water filters, toothpaste,
car polish, paints, etc.
Sediments Song…
• http://www.youtube.co
m/watch?v=rvh_DnwrD
dM