Lesson 2b
Global Features of the Earth
Why is this important to this class?
• We understand the inner workings of the
Earth better than any other planet.
• Interior activity leaves tell tale signs on the
surface of the Earth. (Tectonics)
• Finding these same signs on other planets
gives us information about their inner
workings.
• We will use the Earth as a starting point to
understand the Solar System.
From antiquity, we have known the
inside of the Earth is hot.
• The Earth is filled with a volume of very hot,
molten material. When it is inside the Earth
we refer to this as magma. On the surface it is
lava.
• Tectonics -- distortion of the earth's crust
resulting from the forces within the Earth.
Distortions occur within the earth's crust
causing structural deformation
All tectonics occurs because hot magma rises
from inside the Earth, to cooler regions nearer
the surface.
The basic process is very easy to
understand.
• Material near the surface of the Earth is cool.
The hot material inside the Earth rises toward
the surface forcing cooler material to sink.
• It is this motion that causes all tectonics on
the Earth (and terrestrial planets).
• The interior of the Earth is cooling over time,
but all cooling has to take place at the surface
of the Earth. Otherwise the heat is trapped
inside.
• Lithosphere – The rigid outer layers of the
Earth consisting of the continental crust, the
oceanic crust, and the upper mantle.
• Asthenosphere -- A zone of the earth's mantle
that lies beneath the lithosphere and consists
of several hundred kilometers of deformable
rock.
• Below the mantle is a liquid outer core and
inside of that is a solid inner core.
• Let’s put our crust in perspective.
• Continental crust is ~ 10 km thick
• The radius of the Earth is 6,378 km.
• The ratio of crust thickness to Earth radius is
• 10km/6378km = 0.0015
• If the radius of the Earth was 10 meters the
crust would only be 1.5 centimeters.
• If the radius of the Earth was 10 meters the
crust would only be 1.5 centimeters.
• While we are at it, lets consider the
atmosphere.
• What is a good estimate of the height of the
Earth’s atmosphere?
What is a good estimate of the height
of our atmosphere?
1.
2.
3.
4.
About 2.5 km.
About 25 km.
About 250 km.
About 2500 km.
• Above 25 km, the atmosphere is so thin that
only rocket planes can fly. So let’s use that.
• On a 10 meter Earth radius scale the
atmosphere is 2.5 centimeters tall.
How far away is the ISS?
• The ISS is orbiting the Earth.
• How far away do you think the ISS is, when
you compare it to the distance to the Moon?
1. The ISS is about halfway to the
Moon
2. The ISS is about one-tenth of the
way to the Moon.
3. The ISS is about one-hundredth
the way to the Moon
4. About one-thousandths the way
to the Moon
.
• Above 25 km, the atmosphere is so thin that
only rocket planes can fly. So let’s use that.
• On a 10 meter Earth radius scale the
atmosphere is 2.5 centimeters tall.
• The ISS orbits at 350 km. On the 10 meter
scale, it is 55 centimeters above the surface.
• The Moon is 384,000 km away. On this scale it
would be 600 meters away.
Interior of the Earth
• Deepest hole ever drilled in the Earth was by the
former Soviet Union. They drilled to a depth of
12.2 km after 24 years of drilling.
• We get some information from lava that makes it
to the surface of the Earth
• But structure wise, all information comes from
seismology.
• Seismology is the study of earthquakes and
seismic waves that move through and around the
earth
Earth – A water world?
Waves
• There are two general types of waves.
Transverse and Longitudinal.
• Earth quakes have both types. They are called
S-waves and P-waves
Waves
• There are two general types of waves.
Transverse and Longitudinal.
• Earth quakes have both types. They are called
S-waves and P-waves
Which type of
wave do you think
can propagate
through a liquid?
1. Only the S-Wave since you
can’t push and pull a liquid
2. Only the P-wave since a
liquid won’t restore the sideto-side motion
3. Neither S-Waves or P-Waves
4. Both S and P-waves
.
Model
of
Seismic
activity
inside
the
Earth
• Observing arrival of S and P-waves shows the
size and liquid nature of the outer core.
• Reflections and refractions between more
dense and less dense regions gives further
information about structure.
• Also, waves move at different speeds through
different types of material. So the arrival time
of the wave also has information about the
internal structure of the Earth.
The Continents
• From the time of the early European explorers
it was noticed that South America and Africa
seem to fit together.
• Alfred Wegner in 1915 suggested that the two
continents were once connected. This was, in
part, based on the geologic similarities
between the two coasts and the shared fossil
species found on each continent.
• Theory found little favor, because there was
no known physical mechanism to push whole
continents around.
Important advances
• World-wide seismometers to measure
earthquakes.
• Discovery of mid-Atlantic rift and stripes of
magnetic reversal.
Earthquake Epicenters 1980-1990
Pacific Basin region
Volcanoes of the Earth
Mountain Ranges of the Earth
What is the evidence so far?
• Majority of Earthquakes occur at plate
boundaries. Particularly around the Pacific
basin. (The Ring of Fire).
• The majority of volcanoes are located at plate
boundaries. Particularly in the Ring of Fire.
• Mountain ranges are also located at plate
boundaries.
• The continents appear to be on the move. But
what is doing the pushing?