Earth’s Interior Section 1.1
1. The Science of Geology
 Earth’s hard surface is formed of rock.
 The study of planet Earth is called geology.
 Geologists concluded that Earth’s landforms
are the work of natural forces that slowly
build up and wear down the land.
 Constructive forces, such as volcanoes, shape
the surface by building up islands and
landmasses.
 Destructive forces, such as ocean waves,
shape the surface by slowly wearing away
beaches and other features.
 Geologists cannot observe earth’s interior
directly.
 It is over 6,000 kilometers from the surface
to the center of Earth.
 Seismic waves are produced by earthquakes.
2. A Journey to the Center of the Earth.
 The temperature increases, at first quickly
and then more slowly.
 Pressure increases as you go from the
surface to the center of Earth.
 The three main layers that make up the
Earth’s interior are the crust, mantle and
core.
3. The Crust
 The crust is a layer of rock that forms Earth’s
outer skin.
 The dark-colored rock that makes up most of
the oceanic crust is basalt.
 The light-colored rock that makes up most of
the continental crust is granite.
4. The Mantle
 The mantle is a layer of hot rock between the
crust and core.
 The lithosphere is a rigid layer that includes
the upper part of the mantle and crust.
 The asthenosphere is a soft layer just below
the lithosphere.
5. The Core
 The core contains iron and nickel.
 The core is under extreme pressure.
6. Earth’s Magnetic Field
 Currents in the liquid outer core force the
inner core to spin.
 Earth’s magnetic field is created by the inner
core spinning faster than the rest of Earth.
Inside Earth 1.2
Convection Currents and the Mantle
1. Introduction
 The movement of energy form a warmer
object to a cooler object is called heat
transfer.
 Three types of heat transfer are radiation,
conduction and convection.
2. Radiation
 Radiation is the transfer of energy through
empty space.
 Forms of radiation include the heat you feel
from sunlight and the heat you feel around a
flame or open fire.
3. Conduction
 Conduction is heat transfer by direct contact
of particles of matter.
 An example is a spoon heating up in a pot of
hot soup or the skin of your hand heating up
when you touch the hot spoon.
4. Convection
 Convection is the heat transfer by the
movement of a heated fluid (liquid or gas).
 Heat transfer by convection is caused by
differences of temperature and density within
a fluid.
 A measure of how much mass there is in a
volume of a substance is density.
 When a fluid’s temperature increases its
density decreases.
 The currents will stop flowing when all the
soup has reached the same temperature.
5. Convection in Earth’s Mantle
 Convection currents flow in the
asthenosphere.
 The heat source for the convection currents is
the Earth’s core.
Drifting Continents
1. The Theory of Continental Drift
 Wegener’s hypothesis was that all the
continents had once been joined together in a
single landmass and have since drifted apart.
 Wegener named his supercontinent Pangaea.
 Wegener thought that this supercontinent had
broken apart and that the pieces had slowly
moved to become the continents as they are
today.
 Wegener’s idea that the continents slowly
moved over Earth’s surface became known as
continental drift.
 Some examples that help prove this theory are
the mountains in south Africa that line up with
mountains in Argentina, and coal fields in
Europe that match up with coal fields in North
America.
 Any trace of an ancient organism preserved in
rock is called a fossil.
 Wegener explained his finding similar fossils
on different continents as evidence that the
continents were at one time united.
 Wegener believed that the continents
positions changed but not the Earth’s climate.
2. Scientists Reject Wegener’s Theory
 Wegener believed that mountains formed when
continents collided with each causing the
edges to crumple and fold.
 Mountains usually occur in narrow bands along
the edges of continents, as you would expect
if the collision of continents forms mountains.
Sea-Floor Spreading
 Mapping The Mid-Ocean Ridge
 The mid-ocean ridge is the longest chain of
mountains in the world
 The top of the mid-ocean ridge is split by a
steep-sided valley
 A device that bounces sound waves off
underwater objects is called sonar.
 Sonar is used to determine the distance to
an object. It has been used to map the
mid-ocean ridge.
 Evidence for Sea-Floor Spreading
 The process that continually adds new
material to the ocean floor is called seafloor spreading.
 The three types of evidence for sea-floor
spreading are molten material, magnetic
stripes and drilling samples.
 At times in the past, a compass needle would
have pointed south.
 Rock that makes up the ocean floor lies in a
pattern of magnetized stripes.
 Rocks that harden at the same time have
the same “magnetic memory.”
 The farther away form the ridge that the
samples were taken, the older they are and
the youngest samples were always in the
center of the ridge.
 Subduction at Deep-Ocean Trenches
 Deep underwater canyons are called deepocean trenches.
 Subduction is the process by which the
ocean floor sinks beneath a deep-ocean
trench and back into the mantle.
 Subduction and Earth’s Oceans
 The Atlantic Ocean is expanding because it
has only a few deep-ocean trenches, so the
spreading ocean floor has virtually nowhere
to go.
The Theory of Plate Tectonics
 Introduction
 The lithosphere is broken into separate
sections called plates.
 A Theory of Plate Motion
 A scientific theory is a well-tested concept
that explains a wide range of observations.
 Pieces of Earth’s lithosphere are in
constant, slow motion, driven by convection
in the mantle.
 Plate Boundaries
 Plate boundaries are lines where different
pieces of the lithosphere meet.
 A fault is a break in Earth’s crust where
rocks have slipped past each other.
 Rift valleys are deep valleys that form
where two plates pull apart.
 Most divergent boundaries occur at the
mid-ocean ridge.
 When two plates converge, the result is
called a collision
 The density of the plates determines
which plate comes out on top.
 The Continents’ Slow Dance
 Plates move from about one to ten
centimeters per year.