The Earth
How Far….
• The moon’s distance from earth averages
388,000 km (240,000 mi); we have been
there.
The earth’s distance to mars is about
72,400,000 km (45,000,000 mi).
• We’ve sent rockets and probes to Mars!
The earth is about 6380 km (3975 mi)
from crust to core.
• … But, we haven’t been anywhere close to
there yet!!
• How deep have we gone into the earth?
• The deepest we have ever been was
about 12 km (7.5 mi).
• Why do you think we can go millions of
miles into outer space, but less than 15 km
(10 mi) into the earth??
Let’s look at the breakdown of the
earth.
The earth is made up of 3 major sections.
• The crust
• The mantle
• The core
This can be broken down a bit
more…
• The mantle can be divided into the upper
and lower mantle
• And…
• The core can be divided into the outer and
inner core.
A picture is worth a 1000 words.
• Let us look at a cut out, or a
cross-section of the earth.
• What is a cross section?
What’s inside this pie?
What’s inside the earth?
Let’s see!
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 crust is only about 3-5 miles (8 kilometers)
thick under the oceans (oceanic crust) and
about 25 miles (32 kilometers) thick under the
continents (continental crust).
There are two types of crust;
oceanic, and continental.
•Oceanic crust:
As the name already suggests, this crust is below the
oceans. The rocks of the oceanic crust are very young
compared with the rocks of the continental crust. The
rocks of the oceanic crust are not older than 200
million years. The average density of the oceanic crust
is 3g/cm³.
Continental crust:
The earth's crust is the thickest below the continents,
with an average of about 20 to 25 miles (30 to 40 km)
and with a maximum of 45 miles (70 km); this would
be at the mountain peaks.. The continental crust is
older than the oceanic crust, some rocks are 3.8
billion years old. The continental crust mainly
consists of igneous rocks.
The average density of the continental crust is
2.7g/cm³.
So, what is density?
• Take a look at the two boxes below. Each
box has the same volume. If each ball
has the same mass, which box would
weigh more? Why?
Density cont.
The box that has more balls has more
mass per unit of volume. This property
of matter is called density. The density
of a material helps to distinguish it from
other materials. Since mass is usually
expressed in grams and volume in
cubic centimeters, density is expressed
in grams/cubic centimeter.
We can calculate density using the formula:
Density= Mass/Volume
.
Examples of Density
• First, we take a “size” or amount. In this
case, one cubic centimeter.
Density cont.
• Then we take a mass.
** Remember** Mass is not weight, but instead, it is the
amount of matter occupying a particular space.
Then we divide mass by the
volume.
So, gold for instance, has
19.3 grams per cubic
centimeter. Silver has 10.5
grams per cubic centimeter.
The density of a
marshmallow is .5 grams
per cubic centimeter.
Which has more mass? Which is
more dense?
Crust cont.
• The temperatures of the crust vary from air
temperature on top to about 1600 degrees
Fahrenheit (870 degrees Celsius) in the
deepest parts of the crust. You can bake a
loaf of bread in your oven at 350 degrees
Fahrenheit , at 1600 degrees F. rocks
begin to melt.
The Mantle
• Below the crust is the mantle, a dense, hot
layer of semi-solid rock approximately 2,900
km thick. The mantle, which contains more
iron, magnesium, and calcium than the crust,
is hotter and denser because temperature
and pressure inside the Earth increase with
depth.
The upper portion of the mantle can be equal
to, or sometimes even less dense than
oceanic crust. It ranges between 2.9 and 3.3
g/cm³.
The lower portion of the mantle increases in
density the deeper it gets. It ranges
from 4.6 - 5.4g/cm³.
As a comparison, the mantle might be thought of
as the white of a boiled egg.
The Core
• At the center of the Earth lies the core, which is nearly
twice as dense as the mantle because its composition is
metallic (iron-nickel alloy) rather than stony. Unlike the
yolk of an egg, however, the Earth's core is actually
made up of two distinct parts: a 2,200 km-thick liquid
outer core and a 1,250 km-thick solid inner core. As the
Earth rotates, the liquid outer core spins, creating the
Earth's magnetic field.
Outer Core
• Outer Core
The core of the Earth is like a ball of very
hot metals. (4000 degrees F. to 9000
degrees F.) The outer core is so hot that
the metals in it are all in the liquid state.
The outer core is located about 1800 miles
beneath the crust and is about 1400 miles
thick. The outer core is composed of the
melted metals nickel and iron.
It’s density is about 11.5 g/cm³.
Inner Core
The inner core of the Earth—even more dense than the
outer core (13 g/cm³)—has temperatures and pressures so
great that the metals are squeezed together and are not
able to move about like a liquid, but are forced to vibrate in
place as a solid. The inner core begins about 4000 miles
beneath the crust and is about 800 miles thick. The
temperatures may reach 9000 degrees F. and the
pressures are 45,000,000 pounds per square inch. This is
3,000,000 times the air pressure on you at sea level!!!
By understanding what makes up the interior
of the earth, we can see what effects it has
on the surface.