Transcript The Earth - Cardinal Newman High School

THE EARTH
Interior
Crust
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layer of rock that forms Earth’s skin
includes dry land and ocean floor
most places 5- 40 km thick
in a few places, under mountains, can be as
thick as 70 km
similar to skin of onion
Mantle
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made of hot rock, but solid
nearly 3000km thick
three regions:
Lithosphere
 upper part
 similar to crust- rigid
 100km
Asthenosphere
 hotter and ↑ pressure
 like soft tar
Lower Mantle
 Hotter, but still solid
Core
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made mostly of iron and nickel
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two parts:
 liquid outer core
 solid inner core
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heat has melted metals in outer core
pressure in inner core is so great molecules
cannot spread out to the liquid formation
this results in the metals being forced into the
solid state
recent evidence has shown inner core may
contain O, S, Si
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Earth’s Magnetic Field
believe that movement of liquid
outer core creates magnetic field
 remember that Earth acts like a
giant bar magnet
 the field around the magnet is the
magnetosphere
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Convection
is the flow that transfers heat
within a fluid
 heating and cooling of the fluid,
changes in the fluid’s density, and
the force of gravity combine to set
convection currents in motion
 these currents continue as long as
heat is added
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Convection
Convection in Earth
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in Earth’s mantle large amounts of
heat are transferred by convection
currents
heat from the core and the mantle
itself causes currents
this rising and sinking happens over
thousands/ millions of years
there may also be currents in the
outer core
this plus the nickel and iron cause the
magnet in the Earth
Continental Drift
in 1910 a German scientist, Wegener
hypothesized that all the continents were
once joined together in a single landmass and
have since drifted apart
•this idea that the continents/ crust moves is
called CONTINENTAL DRIFT
•the one continent has been called Pangaea
•he gathered evidence from different areas to
support his idea
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Pangaea
-All continents one land mass surrounded by
ocean
Evidence for Continental Drift
He could see
the evidence,
but could not
explain the
way the
earth’s crust
moved.
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evidence is from:
land features
fossils
climate change
Land Features
rocks and formations of rocks support the
evidence of continental drift
 the theory of Pangaea rock formations in
Africa (west) line up with one in South
America (east)
 Brazil has coal fields with identical layers
found in Africa
 Glacial erosion also exists in SA, Africa, India,
and Australia that match similar patterns
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Fossils
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similar fossils have been found in SA and Africa
Glossopteris is an extinct fern
This fossil found in rocks approx 250 my old and is
found in Africa, India, and Antarctica
seeds from these plants were too large to be
dispersed by wind from one continent to the
other
the seeds could only be dispersed in smaller areas
like joined lands
Climate Change
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salt, coal, and limestone support evidence that
continents had very different climates long ago
it is not due to climate change, but rather change in
position of the lands
today most salt deposits range from 10-30ْ
latitude
rock salt has been found in MI
coal is only formed in warm swampy climates
today coal deposits have been found in Antarctica
limestone from coral reefs found in Texas and central
US
Wegener’s theory of Continental Drift
was rejected at the time
 Other geologist acknowledged the
evidence
 But they did not know or understand
how the continents could move (no
known mechanism)
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Lithosphere
A portion of the earth that
includes the crust and the upper
part of the mantle that acts as one
unit in its motion
 Can be different in its composition
and softness
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Earth’s Layers
Earth’s Upper Layers
MOVEMENT OF THE CRUST
Observation meets theory!
Mid-Ocean Ridges
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cracks or vents found on the Earth’s crust of the
ocean floor (oceanic crust)
these areas rise above the surrounding crust
underwater mountains, but most are under
hundreds of meters below surface
a few are above the water (island of Iceland,
islands in the Philippines)
underwater volcanoes
discovered through sonar
Sea Floor Spreading
in 1960 Hess, an American
geologist, proposed the sea floor
spreads apart along both sides of a
mid-ocean ridge as new crust is
added
 the ocean floor is like a conveyor
belt, carrying the continents along
with them
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Mid-Ocean Ridge
New crust being made
Trenches
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if this theory is true the mid-ocean ridges
produces new crust through volcanic eruptions
and the floor spreads slowly
at some point the floor (conveyor belt) must
return
at ocean trenches the crust undergoes
SUBDUCTION
subduction is the process by which ocean floor
sinks beneath a deep-ocean trench and back into
the mantle
new oceanic crust is hot coming out of ridge, but
it cools as it moves away and then sinks
this takes ten of million of years
 because of this process the ocean
floor is renewed every 200M years
 the Pacific Ocean is shrinking
 the Atlantic Ocean is growing
 see figure
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Evidence for Ocean Floor Spreading
Molten Material
 Magnetic Stripes
 Drilling Samples
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Molten Material
in 1960 a very small specialized
sub, ALVIN, examined some ridges
 it found rocks shaped like pillows
 such rocks only form when
material hardens quickly after
erupting under water
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Magnetic Stripes
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earth is like a gigantic magnet
oddly at times the poles reverse themselves
last time 780,000 years ago
the rocks in the oceanic crust made up of iron
hold this record of the magnetic field as it comes
out of ridge
using sensitive instruments scientist can record
the magnetic memory of the rocks
the ocean floor shows stripes of these fields
Drilling Samples
Glummer Challenger, a drilling ship, sent
drilling pipes through the water 6Km deep
 samples from sea floor were aged
 farther away from a ridge the samples
were older
 youngest around a ridge
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Sea Floor Spreading
Subduction
Trench
Subduction
PLATE TECTONICS
Putting it all together
The Theory
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in 1965 a Canadian scientist, Wilson, discovered
there are cracks in the continents similar to
those on the ocean floor
he saw the lithosphere was broken into pieces
he called PLATES (both oceanic and continental
plates)
Wilson combined the knowledge of plates, seafloor spreading, and continental drift to come
up with one unifying theory
Plate Tectonics
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the theory of PLATE TECTONICS explains the
formation, movement, and subduction of Earth’s
plates
pieces of Earth’s lithosphere are in slow constant
motion driven by the convection currents of the
mantle
during subduction gravity pulls one edge of a plate
down into the mantle
the rest of the plate also moves
as the plates move, collide, pull apart, or grind past
each other amazing changes occur in Earth’s surface
Earth’s Plates
Plate Boundaries
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the edges of plates meet at plate
boundaries, deep in lithosphere
FAULTS occur at these points
Faults are breaks in the Earth’s crust
where rocks have slipped past each
other (major points of earthquakes)
Plate Boundaries
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there are three types of
boundaries:
Divergent
Convergent
Transform
Divergent
the point where two plates move
apart
 most occur along mid-ocean ridges
where sea-floor spreading occurs
 some do happen on land
 on land, a huge rift valley forms
 e.g. Great Rift Valley in Africa
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Convergent
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place where plates come together, collisions
this results in a collision
the density of plates will determine what will
happen
oceanic crust becomes cooler and denser as it
spreads away from the mid-ocean ridge
Pressure of water also condenses oceanic crust
In general oceanic plates (OP) more dense than
continental plates (CP)
When 2 OP plates converge the denser sinks
under the other less dense plate
 When OP and a CP collide, the OP is more
dense than CP and will slide under the CP
 when 2 CP collide they are too close in
densities for subduction
 instead the plates collide and squeeze the
crust into huge mountain ranges
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Transform
a place where two plates slip past each
other
 no subduction occurs
 no crust is created or destroyed
 high earthquake activity at these points
 all this moving of the plates containing
ocean and continents have shaped the
surface of the Earth since its formation
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