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Formation and Layers of Earth
A little about Earth’s background…

Approximately 4.6 billion years ago,
scientists believe that the Earth and other
planets in the solar system formed.
◦ The formation of the planet generated heat
from gravitational energy and the decay of
radioactive elements, which are still present
on Earth today!
Let’s go to China!!
If you wanted to dig a hole to China, do
you think you would be able to? Why or
why not?
 Compare this apple slice to the interior
of the Earth. How does each layer of the
apple correspond to each layer of the
Earth?

Revised from: http://www.slideshare.net/melissameasley/earth-layers-density
Why haven’t we explored inside of
the Earth?
We have explored
outer space much
more extensively
than we have
explored the inside
of our own planet.
 Why haven’t we
explored the inside
of our planet more
completely?

Reason 1- HEAT

Heat
 The Earth gets hotter as it gets
deeper.
 The Earth gets up to 9000 degrees
F in the inner core.
▪
▪
▪
▪
Crust = 0 -1598 F
Mantle = 1598 F – 3992 F
Outer Core = 3992 – 9032 F
Inner Core = 9032 F+
 The Kola peninsula drilling project
well (in Russia) reached
temperatures of 180 degrees C
(356 degrees F), and they weren’t
even halfway through the crust!
▪ Food cooks well at 350 degrees F.
Reason 2- PRESSURE
◦ The pressure increases as depth increases in
the Earth from all the layer and matter on top
of it squishing it down.
◦ Just 30 miles down into the Earth the
pressure reaches pressures of around 200,000
psi.
 Your bike tire only hold around 32 psi. (psi =
pounds per square inch).
◦ The pressure at the center of the earth is
estimated at around 5 million times
atmospheric pressure (the 15 pounds/square inch that
we breathe and live in).
Reason 3- Earth isn’t Accessible
 Getting into the earth is very
difficult because of tremendous
heat and pressure.
 The Kola peninsula drilling
project well (in Russia) was the
deepest well ever drilled into
the Earth. It took 24 years, and
it is less than 13 kilometers
(about 7.6 miles) deep.
 This is less than halfway
through Earth’s crust.
 The furthest humans have
traveled is 3.5 km (about 2.2
miles) in mines in South Africa
to extract gold.
Reason 4- DENSITY




Three centuries ago, the English
scientist Isaac Newton
calculated the density of the
inside layers of the Earth as
twice that of surface rocks.
Our knowledge of what's inside
the Earth has improved
immensely since Newton's time,
but his estimate of the density
remains essentially unchanged.
Look at the chart at right.You
can see that the density of Earth
materials increase as depth
increases.
The matter in the Earth is
simply too compact to be able
to work through.
Layer
and
Overall
Thickness
Layer is Made
of?
Density of the
Layer
Inner Core 5150-6500 Solid Iron and
km
Nickel
13.0g/cm3
Outer
Core
2900-5150 Liquid Iron and
km
Nickel
11.5g/cm3
Mantle
32-2900
km
4.5g/cm3
Si, O2,Fe,Mg
Upper layer is
mostly rocks
Lower Layer is
more iron and
nickel
Crust
0-32 km
Si, O2, Al, Ca,
Fe, Na, K, Mg
Mostly rocks
2.7- 3.0g/cm3
Why is the inside of the Earth
divided into layers?
By the end of the day today, you should be
able to…
1. Define density.
2. Explain the difference between objects
that are more dense and objects that
are the least dense.
3. Identify objects that are more dense and
less dense in comparison to each other
4. Relate these concepts to Earth’s layers.
What do we call this?
The Earth has 4 separate layers…
How do we know this, anyway?
 Brief explanation of seismic waves:
http://www.youtube.com/watch?v=yOGoKCK17a4 (1:40)
(We will discuss seismic waves in much
more depth later! For now, just know that
these waves have “shown” us that there
are different layers, even when we cannot
physically see them!)
First, some density background
information (this should be review):
Density = mass/volume
 Density is the science-y word for “heavy”
 More dense materials sink
 Less dense materials float
 Gravity pulls ___________________.

Question to ponder…

Why does Earth’s interior separate into
layers instead of mixing together?
◦ Answer this at the top of your density column
page!

We will do a lab today to show you why!
Density Column Lab!
What does the density column lab
tell you about Earth’s layers?
As the planet was formed, the heavier
elements sunk to the core of the earth,
while the less dense elements stayed in
the crust.
 Planetary differentiation – a process
where more dense materials sink to the
center, while less dense materials stay on
the surface.

Layers of the Earth Rap video:
http://www.youtube.com/watch?v=Q9j1xGaxYzY
The Layers of the Earth
© Copyright 2006. M. J. Krech. All rights reserved.
The Four Layers
The Earth is composed
of four different layers.
1.
The crust is the layer
that you live on, and it is
the most widely studied
and understood.
2.
The mantle is much
hotter and has the
ability to flow.
The Four Layers
(continued)
The outer core and
inner core are even
hotter with pressures so
great you would be
squeezed into a ball smaller
than a marble if you were
able to go to the center of
the Earth!
The Crust
The Earth's Crust is like the
skin of an apple. It is very thin
in comparison to the other
three layers.
The thickness of the crust
varies.
Crust beneath the ocean, called
oceanic crust is less than 10
km thick
Crust beneath the continents ,
called the continental crust,
is about 32 km thick.
The Lithospheric Plates
The crust and the stiff upper part of the mantle
together make up the rocky lithosphere.
The Lithospheric Plates
The crust and the whole lithosphere are broken into
many parts called plates.
The Asthenosphere
The plates "float" on the
softer part of the upper
mantle, called the
asthenosphere.
This allows the plates to
move.
Occasionally they will stop
moving but when they stick
in one place they build
pressure until then snap.
The Lithosphere
The crust and the upper layer of the
mantle together make up a zone of rigid,
brittle rock called the Lithosphere.
The Crust
The crust is composed of two rocks. The continental
crust is mostly granite. The oceanic crust is basalt.
Basalt is much denser than the granite. Because of this
the less dense continents ride on the denser oceanic
plates.
The Mantle
The Mantle is the
largest layer of the Earth.
The mantle is made up of
extremely hot rock
composed of the
elements silicon, iron,
oxygen, magnesium and
sulphur.
The Mantle
The boundary between the
crust and the mantle is
called the Moho.
Here the temperature of
the Earth is about 870C.
As you get deeper into the
mantle the temperature
rises until it reaches a top
heat of around 3700 C.
Convection Currents
The middle mantle "flows"
because of convection
currents. Convection
currents are caused by
the very hot material at
the deepest part of the
mantle rising, then cooling
and sinking again -repeating this cycle over
and over.
Convection Currents
The next time you heat anything
like soup or water in a pan you can
watch the convection currents
move in the liquid. When the
convection currents flow in the
asthenosphere they also move the
crust. The crust gets a free ride
with these currents, like the cork
in this illustration
http://www.absorblearning.com/media/attachment.a
ction?quick=12p&att=2775
The Outer Core
The outer core starts at
2,900 km (1,800
miles) beneath the
surface of the Earth
and it is about 2,350
km thick.
At its hottest point the
outer core will reach a
temperature of
6,100C.
This is so hot that the
entire layer is liquid.
The Outer Core
This area of the Earth is
made up of molten
nickel and iron.
This moving mass of
molten metal together
with the inner core
creates Earth's
magnetic field.
The Inner Core
The inner core
begins at 5,150 km
(4000 miles) below the
Earth’s surface.
The inner core is about
1,300 km (800 miles)
thick.
The highest temperature
is 7,000C.
The Inner Core
At this temperature the
iron and nickel that
make up the inner core
would be liquid were it
not for the intense
pressure in this layer.
Because of the pressure
the inner core is solid.
The End
BONUS:
Find a pair or trio and answer
this question:
Have we ever seen part
of the Mantle? Explain.
© Copyright 2006. M. J. Krech. All rights reserved.