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Plate Tectonics
Exploring Inside the Earth
Geologists have used evidence from rock
samples and evidence from seismic waves to
learn about Earth’s interior.
Geologists
are scientists
who study
the forces
that make
and shape
planet Earth.
Geology
is the
study of
planet
Earth.
Studying Surface Changes
Constructive forces
shape the surface by
building up mountains.
Destructive forces are
those that slowly wear
away mountains and,
eventually, every other
feature on the surface.
The Crust
The crust is a layer
of solid rock that
includes both dry
land and the ocean
floor.
Three main layers make up
Earth’s interior: the crust,
the mantle, and the core.
Each layer has its own
conditions and materials.
The Mantle
Earth’s mantle is made up of rock that is very hot,
but solid. The mantle is divided into layers
based on the physical characteristics of those
layers.
The Core
The core is made mostly of the metals iron and
nickel. It consists of two parts–a liquid outer
core and a solid inner core.
Types of Heat Transfer
There are three types of heat transfer:
radiation, conduction, and convection.
Radiation –
the transfer of
energy
through empty
space
Conduction –
heat transfer by
direct contact of
particles of
matter
Heat
transfer –
the
movement
of energy
from a
warmer
object to a
cooler
object
Convection Currents
Heating and cooling of the fluid, changes in
the fluid’s density, and the force of gravity
combine to set convection currents in
motion.
Convection
– heat
transfer by
the
movement
of a h eated
fluid
Convection
currents –
the flow
that
transfers
heat within
a fluid
Convection Currents in Earth
Heat from the core and the mantle causes
convection currents in the mantle. This is
how the heat is transferred.
Continental Drift
Wegener’s hypothesis was that all the continents were
once joined together in a single landmass.
Continental drift – The idea that the continents slowly
moved over Earth’s surface.
Scientists now believe that about 250 million
years ago, a super-continent known as Pangaea
existed. This super-continent was made up of all
the continents on Earth.
Evidence for Continental Drift
Fossils – any trace of an ancient organism that
has been preserved in rock.
Wegener could not provide a
satisfactory explanation for the force
that pushes or pulls the continents.
Mid-Ocean Ridges
The East Pacific Rise is just one of the many midocean ridges that wind beneath Earth’s oceans.
The midocean
ridge is
the
longest
chain of
mountai
ns in the
world
Sonar –
a device
that
bounces
sound
waves
off
underwater
objects
and then
records
the
echoes
of these
sound
waves
What Is Sea-Floor Spreading?
In sea-floor spreading, the sea floor spreads apart along
both sides of a mid-ocean ridge as new crust is added
to the ocean floor. As a result, the ocean floors move
like conveyor belts, carrying the continents along with
them.
Evidence for Sea-Floor Spreading
Several types of evidence supported the theory of
sea-floor spreading: eruptions of molten
material, magnetic stripes in the rock of the
ocean floor, and the ages of the rocks
themselves.
Subduction at Trenches
In a process taking tens of millions of years, part of the ocean
floor sinks back into the mantle through deep-ocean trenches.
Deep-ocean trenches are deep underwater canyons formed
where the oceanic crust bends downward.
Subduction – the process by
which the ocean floor sinks
beneath a deep-ocean trench
and back into the mantle.
Growing an Ocean
Because of sea-floor spreading, the distance
between Europe and North America is
increasing by a few centimeters per year.
How Plates Move
The lithosphere is broken into separate sections called plates.
The theory of plate tectonics explains the formation, movement,
and subduction of Earth’s plates.
Scientific
theory – a
well-tested
concept
that
explains a
wide range
of
observation
s
Faults –
breaks in
Earth’s
crust
where
rocks
have
slipped
past each
other
Plate Boundaries
There are three kinds of plate boundaries:
1. divergent boundaries 2. convergent boundaries
3. transform boundaries.
A different type of plate movement occurs along each type of boundary.
Rift valley
– a deep
valley that
forms
along the
divergent
boundary
Plate Boundaries
At the locations where two tectonic plates interact,
a boundary between these plates exist. There
are three types of boundaries that geologist
observe. These boundaries are divergent
boundaries, convergent boundaries, and
transform boundaries.
Continental Drift
It has taken the continents about 225 million
years since the breakup of Pangaea to
move to their present locations.
Resources
• http://www.kidsgeo.com/geology-forkids/0037-the-earth-earth-inside-out.php
• Prentice Hall, Inc. Textbook Series