2. Learning Objectives
Describe the composition and structure of the
Describe the Earth’s tectonic plates.
Explain the main cause of earthquakes and
describe their effects.
Identify the relationship between volcanic
eruptions and climate change.
Describe how wind and water alter the Earth’s
3. The Structure and Composition
of the Earth
4. The Earth as a System
The Earth consists of rock, air, water, and
living things that all interact with each other.
There are four parts of the Earth
Biosphere (living things)
5. Discovering Earth’s Interior
Scientists can study the interior of the Earth by
using seismic waves.
Seismic waves are the waves that travel through
Earth’s interior during an earthquake.
A seismic wave is altered by the nature of the
material through which it travels.
Seismologists measure changes in the speed and
direction of seismic waves that penetrate the
interior of the planet.
This has helped seismologists to learn that Earth
is made up of different layers and different
6. The composition of the Earth
The Earth is made of three layers that are
made of denser materials toward the center of
The layers are determined by the chemical
Thin outer layer
5 km to 8 km thick beneath ocean
Oldest is 200 million years old
20 km to 70 km thick beneath continents
Average age is 2 billion years old
Oldest is 3.7 to 4.3 billion years old
64% of the mass of the Earth
2,900 km thick
500ºC to 900ºC (upper portion of mantle)
4,000ºC (near the core)
Melting mantle produces the crust
Radius = 3,400 km
Mostly iron but also contains some nickel.
Temperature is probably around 5,000ºC
10. The Structure of the Earth
The Earth can also be divided into layers
based on physical properties.
Most outer layer
Cool and rigid
15 km to 300 km thick
Includes the crust and uppermost part of
Divided into huge pieces called tectonic plates
Beneath the lithosphere
Plastic, solid layer of the mantle made of rock
that flows slowly. This allows the tectonic
plates to move.
250 km thick
Beneath the asthenosphere
2,550 km thick
Name means the “middle sphere”
14. Outer Core
Beneath the mesosphere
2,200 km thick
Made of liquid nickel and iron
15. Inner Core
The innermost layer of the Earth
1,228 km radius
A sphere of solid nickel and iron at the center
of the Earth.
16. Plate Tectonics
The lithosphere is divided into pieces called tectonic
These plates glide across the asthenosphere like ice
floats across a pond.
The continents are located on tectonic plates and
move around with them.
The major tectonic plates include:
17. Plate Tectonics
18. Plate Boundaries
Much of the geologic activity at the surface of
the Earth takes place at the boundaries
between tectonic plates.
Move away from one another
Collide with one another
Slip past one another
Enormous forces are generated at tectonic
plate boundaries where the crust is pulled
apart, squeezed together or is constantly
19. Mountain Building
When tectonic plates collide, slip by one
another, or pull apart, enormous forces causes
rock to break and buckle.
Where plates collide, the crust becomes
thicker and pushed up and eventually forms a
A fault is a break in the Earth’s crust.
Blocks of the crust slide past each other along
When rocks that are under stress suddenly
break, a series of ground vibrations is set off.
These vibrations are known as earthquakes.
Earthquakes are occurring all the time.
22. The Richter Scale
Used by scientists to quantify the amount of
energy released by an earthquake.
Magnitude - The measure of the energy
released by an earthquake.
The scale goes from 1.0 to 10.0.
Each increase of magnitude by one whole
number is ten times greater and releases 31.7
times more energy than the whole number
Description Earthquake Effects
Less than 2.0 Micro Microearthquakes, not felt. About 8,000 per day
Generally not felt, but recorded. About 1,000 per day
3.0-3.9 Often felt, but rarely causes damage. 49,000 per year (est.)
Noticeable shaking of indoor items, rattling
noises. Significant damage unlikely.
6,200 per year (est.)
Major damage to poorly constructed
buildings over small regions. Slight damage
to well-designed buildings.
800 per year
Can be destructive in areas up to about
160 kilometres (100 mi) across in
120 per year
Can cause serious damage over larger
18 per year
Can cause serious damage in areas
several hundred miles across.
1 per year
Devastating in areas several thousand
miles across. 1 per 20 years
Never recorded Extremely rare
A volcano is a mountain built from magma.
Magma – melted rock that found beneath the
surface of the earth
Located near tectonic plate boundaries where
plates are sliding or separating from one
May occur on the land or under sea.
Under sea volcanoes may eventually break
through the surface as islands.
26. Volcano Eruptions
A volcano erupts when the pressure of the
magma inside becomes so great that it blows
open the solid surface of the volcano.
Some volcanoes have magma flowing out of
them all the time so the pressure never builds
up and they never erupt.
27. Sometime before May 18, 1980
Mt. St. Helens (Washington) Before…
28. May 18, 1980
Mt. St. Helens, During…
29. May 18, 1980
Mt. St. Helens, During…
30. Mt. St. Helens, During…
Mt. St. Helens, During…
31. May 19, 1982
Mt. St. Helens, 2 Years after…
32. Large trees (some over 100 feet tall) flattened by the lateral blast from Mt.
The Lateral Blast
33. An Approaching Ash Cloud
34. The Ash Fallout from Mt. St. Helens
35. Cleaning Up the Ash
36. The Before and After
37. The Mudflow
38. Mt. St. Helens Today
39. Local Effects of Volcano
Volcanic eruptions can be devastating to local
economies and can cause great human loss.
Clouds of hot ash, dust, and gases can flow
down the slope of a volcano at speeds up to
200 km/hour and sear everything in their path.
Volcanic ash can mix with water and produce
Ash that falls to the ground can cause
buildings to collapse, bury crops, damage
engines, and cause breathing problems.
40. Global Effects of Volcanic
Can change Earth’s climate for several years.
Clouds of volcanic ash and sulfur-rich gases
can reach the upper atmosphere.
Ash and gas spread across the planet and
reduce the amount of sunlight that reaches the
Reduced sunlight can result in a decrease in
the average global temperature over a period
of several years.
The Earth’s surface is continually battered by wind
and running water.
This moves rocks around and changes their
Erosion – the removal and transport of surface
Erosion wears down rocks and makes them
43. Water Erosion
Ocean waves erode coastlines.
Rivers can carve deep gorges into the Earth.
44. Water Erosion
45. Wind Erosion
Plant roots hold soil in place. Without plants
the wind can blow soil away very quickly.
Soft rock can be carved away over time.