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Chapter 2.
Earth: unique in the solar system
–Water exists in all three phases
Solid, Liquid, and Gas
70 % covered with liquid water
= Global Ocean
* Atmosphere contains oxygen
* Earth can support life
Basic Earth Characteristics
• Third
rd
(3 )
planet from the sun
• A solid or terrestrial planet
• Approximately
4.6 billion years old
• Shape = oblate spheroid
Layers of the Earth
• CRUST
– thin, rocky
– outermost zone
– Oceanic crust
• Thinner, denser, younger
– Continental crust
• Thicker, less dense, older
• MANTLE
–
–
–
–
middle zone
largely plastic (rock in motion)
Thickest layer
very dense
• CORE
– Earth’s center sphere;
– Made of nickel and iron
Layers of the Earth
• “MOHO”
• Mohorovicic discontinuity
– The boundary between the
crust and the mantle
* Seismic (earthquake) waves
change speed at this
imaginary line.
MOHO
Layers of the Earth
• Lithosphere
– Crust and Upper part of mantle
– Solid (brittle, rigid)
• Asthenosphere
– Upper mantle
– Solid (Less rigid “plastic”)
• Mesophere
– Lower mantle
– Solid (rigid)
• Outer core
– Upper core
– liquid
• Inner core
– Inner core is solid/rigid (due to
high pressure)
• Center of gravity
Structural or
Earth as a Magnet
• Magnetic North
• Produced by the
movement of hot, liquid
iron in the outer core.
• Not the same as:
True or Geographic
North (North Pole)
• The moon and sun may
also have a magnetic
field.
Magnetic North
• Geographic north /True
north. The earth rotates
around the imaginary axis
here.
• Geomagnetic north is located
by a deposit of lodestone (a
magnetic rock) in northern
Canada. The position of this
has changed many times over
the years. It is about 250
miles from True North. A
compass points toward this.
Magnetosphere
– the magnetic field that
surrounds the Earth from
pole to pole.
• When the solar wind
(a stream of radiation
coming from the sun)
hits the earth, the
magnetic field reacts
with it. It protects us!
Solar Wind influences Magnetosphere
Earth’s
Gravity
• Isaac Newton – 1st to describe the effects of gravity.
• The force of attraction between any two objects
depends on the masses of the objects and the distance
between them.
WEIGHT AND MASS
• Earth has a gravitational force
that pulls objects toward the
center (core) of the Earth.
Weight is a measure of the
strength of this pull.
• Unit of weight is a Newton (N)
WEIGHT AND LOCATION
• Weight varies according to
location on Earth. Because Earth
is an oblate spheroid, you would
weigh about 0.3% less at the
equator as you would at the
poles.
• Mass does not change with
location, but weight does.
Internal Sources of Energy
• Internal heat in the core  due to “primitive heat”,
radioactive decay and gravitational contraction.
External Energy Sources
• The sun is the most important external energy source.
• Solar radiation warms Earth’s atmosphere and surface.
• The heating causes the movement of air masses which
generates winds and ocean currents.
HOT
AIR
RISES
CONVECTION
CELL
COLD
AIR
SINKS