Transcript earth - Lake Travis ISD

EARTH Unit 3
Earth's Origin Lesson 1
• While it was still in
the molten state,
separation of elements
occurred within the
earth.
• light inert gasses like
Helium (He) and
Krypton (Kr) were lost
to outer space.
• heavy elements like
Nickel (Ni) and Iron
(Fe) sunk toward the
center.
Earth's Origin
• Several concentric
shells were formed
in and around the
earth, each one
enriched in certain
elements.
• Atmosphere
• Molten crust
• Mantle
• Core
Earth's Origin
• As the earth
cooled, a solid
crust of silicate
rocks formed more
than 4 billion years
ago. This sealed
the hot magma
inside.
• Atmosphere and
oceans
• Solid crust
• Mantle
• Core
Earth's Origin
• Local fractures in
the solid but
relatively thin
crust, led to
extensive volcanism.
• Atmosphere and
oceans
• Solid crust
• Mantle
• Core
Earth Structure
• Earth is a heat
engine.
• Heat is a form of
energy.
• An engine converts
energy from one
form into another
to perform work.
• Earth is constantly
at work.
Earth Structure
• Two major sources
of energy drive
earth processes:
• internal heat
• solar heat
Earth Structure
• Internal heat
drives:
• volcanism
• Plate tectonics
• mountain building
Earth Structure
• Solar heat drives
processes near the
surface such as:
• life
• erosion
• water cycle
• cars (fossil fuels)
• waves
Earth Structure
• The internal source of
heat is revealed by the
geothermal gradient.
(the progressive
increase in
temperature with
depth). High
geothermal gradients
(~ 60 degrees/km) are
typical of volcanic
areas.
• Low geothermal
gradients (~ 10
degrees/km) are found
in areas of thick,
stable continental
Earth Structure
• Low geothermal
gradients (~ 10
degrees/km) are found
in areas of thick,
stable continental
crust.
Earth Structure
• Internal heat
sources are related
to:
• primordial heat
• radiogenic heat
Earth Structure
• Distribution of
internal heat tends
to become uniform
through
redistribution.
Earth Structure
• Redistribution of heat is achieved through:
• Conduction
• Convection
Earth Structure
• The most impressive work done by "Earth's
Heat Engine" is associated with convection.
Earth Structure
•
•
•
•
Convection is responsible for:
Plate movement (plate tectonics)
volcanism
mountain building
Earth Structure
• The Atlantic Ocean began forming almost
200 million years ago. It is still enlarging.
NEXT LESSON
INTERNAL
STRUCTURE and
Seismology
INTERNAL STRUCTURE and Seismology
Unit 3 Lesson 2
• The seismic tool is
used to determine
the thickness of
each of the earth's
internal shells.
INTERNAL STRUCTURE and Seismology
•
•
•
•
The earth's crust is:
thin (5-20 km) under oceans
thick (25-40 km) under continents
separated from the mantle by the Mohorovicic
discontinuity (MOHO)
INTERNAL STRUCTURE and Seismology
INTERNAL STRUCTURE and Seismology
• The mantle behaves
as a :
• fluid when energy
input is slow (i.e.
plate motion)
• solid when energy
input is rapid (i.e.
seismic waves)
INTERNAL STRUCTURE and Seismology
INTERNAL STRUCTURE and Seismology
SEISMOLOGY
• The very deep
internal structure
and composition of
the Earth, below
the depth to which
a well can be
drilled, can be
surmised from
studies of:
• stressed materials
• meteorites
• lab experiments
SEISMOLOGY
• Seismology is a tool
for mapping
subsurface layers.
It measures the
travel time of
energy waves within
the earth.
SEISMOLOGY
• When the energy
waves encounter a
change in rock
density, refraction
and reflection
occur. Some of the
energy is bounced
back to the surface
(reflection) and
some continues
downward at a new
and different
speed and direction
(refraction).
SEISMOLOGY
• Seismic energy can be transmitted as
different waves:
• P
pressure or primary waves
• S
shear or swing waves
SEISMOLOGY
• P-waves vibrate in the same direction as the wave
travels. They are sometimes called primary waves
because they travel fast and arrive at the
recording station before S-waves. They can be
transmitted through both liquids and solids.
SEISMOLOGY
• S-waves, sometimes called shear waves,
vibrate perpendicular to the direction of
travel. They do not transmit through
fluids.
SEISMOLOGY
• S-waves are lost
deep within the
earth at the
boundary between
the mantle and the
outer core. This
indicates that the
outer core is liquid.
SEISMOLOGY
• Abrupt variations in
the velocity of
seismic waves mark
boundaries
(discontinuities)
within the earth.
These indicate
outer margins of
the earth's internal
shells (i.e. mantle,
outer core)
NEXT LESSON
Plate
Tectonics
Plate Tectonics
Unit 3 Lesson 4
CRUSTAL PLATES
Plate Tectonics
• Atlantic Islands are
relatively young
near the MidAtlantic Ridge
(Iceland is about 25
million years old
and still growing).
• older toward the
margins of the
ocean (Canary's are
more than 100
million years old).
Plate Tectonics
• As new crust is formed, iron-rich minerals
in the volcanic lava become aligned with the
earth's magnetic field, recording
paleomagnetic reversals.
Plate Tectonics
• The Earth's magnetic field has reversed
many times
Plate Tectonics
• Symmetrical
magnetic bands on
either side of the
Mid-Atlantic ridge
indicate:
• similar magnetism
• similar age
• ocean spreading
Plate Tectonics
• Seven major Tectonic plates have been
identified along with many smaller ones.
Plate Tectonics
•
•
•
•
PLATE MARGINS are the location of most:
faults
earthquakes
volcanoes
Plate Tectonics
• Earth has a finite surface area, so as new
material is added to the crust, the same
amount of material must be consumed
elsewhere.
Plate Tectonics
• RIFTING occurs and new material is added
to the crust where the plates diverge. The
diagram shows rifting at the Mid-Atlantic
Ridge but it also happens in other places,
for instance the East African rift.
Plate Tectonics
• Ocean crust and continental crust material is
consumed in Subduction Zones. These are places
where heavier oceanic crust slides beneath lighter
rocks of the continental crust. A good example of
this is along the west coast of South America
beneath the Andes.
Plate Tectonics
• Different types of rocks form in different
parts of the Earth's crust. The diagram
shows how this relates to the "rock cycle".
Plate Tectonics
• Large deposits of minerals and fossil fuels
form at the margins of Tectonic Plates
Plate Tectonics
• Tectonic plates change both in position and
direction of movement through time. (note:
the northward drifting of India)
Unit 4
Minerals and
Rocks