Download Inside the Earth

Inside the Earth
Earth’s Structure
Earth’s Layered Structure
• Earth’s interior consists of three major
zones defined by their chemical
composition—
• the crust,
• mantle,
• and core.
Review of Earth’s Interior
• Chemical Classification
• Crust - Thin, rocky outer layer
– Continental Crust:
• Mostly granite
• Average thickness 30km
– Oceanic Crust:
• Mostly basalt
• Average thickness 5 – 8 km
• Denser than continental crust
Divisions in the Earth's Interior
Inside the Earth’s Interior
• Mantle
– Approximately 2900
km thick
– 870o to 2200o
– Composed of silicon,
oxygen, iron and
magnesium
– Upper layer contains
the asthenosphere
http://teach.fcps.net/trt20/projects/EKU/layers/wwr69.gif
Inside Earth’s Interior
• Core
– Approximately 3550 km thick
– 2200o to 5000o
– Composed of iron and nickel
– Tremendous pressure
http://teach.fcps.net/trt20/projects/EKU/Default.htm
Earth’s Layered Structure
http://phschool.com/atschool/earth_science/powerpoints/PHESCh01.ppt#16
Inside Earth’s Interior
• Physical Classification: 5 layers based on
physical traits
• Lithosphere:
– Crust and uppermost part of mantle
– Rigid layer of rock
– “Litho” means stone
– Approximately 100 km thick
Lithosphere
• The Earth’s crust and upper
mantle are broken into
sections called plates
• Plates move around on top of
the mantle like rafts
2 Types of Plates
• Ocean plates - plates below
the oceans made up of mostly
basalt
• Continental plates - plates
below the continents made up
of mostly granite
Inside Earth’s Interior
• Asthenosphere:
– Upper mantle – higher temperature and
pressure
– Soft rock that the lithosphere floats on
– “Asthenes” means weak
– Convection currents in the asthenosphere
cause plates to move
• Mesosphere
– Rest of mantle which is solid material due to
high pressure
Earth’s Outer Core
• At the center of Earth is the core.
• The core is made mostly of iron and nickel and
possibly smaller amounts of lighter elements,
including sulfur and oxygen.
• The core is about 4,400 miles (7,100 kilometers)
in diameter, slightly larger than half the diameter
of Earth and about the size of Mars.
• The outermost 1,400 miles (2,250 kilometers) of
the core are liquid.
• Currents flowing in the core are thought to
generate Earth's magnetic field.
Earth’s Inner Core
• Geologists believe the innermost part of the core, about
1,600 miles (2,600 kilometers) in diameter, is made of a
similar material as the outer core, but it is solid.
• The inner core is about four-fifths as big as Earth's
moon.
• Earth gets hotter toward the center. Geologists believe
the temperature of Earth's outer core is about 6700 to
7800 degrees F (3700 to 4300 degrees C). The inner
core may be as hot as 12,600 degrees F (7000 degrees
C)--hotter than the surface of the sun. But, because it is
under great pressures, the rock in the center of Earth
remains solid.
How deep is deep?
• The deepest mine in the world, a gold
mine in South Africa, reaches a depth
of 3.8 km.
• You would have to travel 1600 times
that to reach the Earth’s center.
• 6,000 km
Exploring the Earth
• Geologist use two main types of
evidence to learn about the Earth’s
interior.
Direct evidence from rock samples.
Indirect evidence from seismic waves.
Rock Samples
• Rocks from inside Earth give
geologists clues about Earth’s
structure.
Rock Samples
• Geologists have drilled holes as deep as 12
km into Earth.
• The drills bring up samples of rocks to study.
• Geologists can make inferences.
• In addition, forces inside the Earth blast rock
to the surface from depths of more than 100
km.
• These rocks provide information about the
interior.
Finding Indirect Evidence
• Seismic Waves
• Primary Waves (P waves)
– Back and Forth motion
– First to arrive after earthquake
– Can travel through liquid and solids
• Secondary Waves (S waves)
– Up and Down motion
– Cannot travel through liquid
Seismic Waves Paths Through the Earth
S Waves
P Waves
http://phschool.com/atschool/earth_science/powerpoints/PHESCh01.ppt#16
Finding Indirect Evidence
• The denser the rock the more quickly the
wave will travel
• As P waves travel from one type of
material to another the waves bend or
refract
• S waves stop at the outer core indicating
that it must be liquid
Finding Indirect Evidence
• The Moho
– The name of the boundary between the
mantle and the crust. Named for Andrija
Mohorovicic
– An area where seismic waves suddenly
speed up (due to rock density)
Shadow Zone
• Absence of P waves from about 105
degrees to 140 degrees around the globe
from an earthquake
• Can be explained if Earth contains a core
composed of materials unlike the overlying
mantle
Earth’s Interior Showing
P and S Wave Paths