Geologic Time
• MYA?
MYA?
MYA?
• MYA stands for Millions of Years Ago
• Geologic time is measured in millions
of years because the time span is so
large.
Geologic Timeline
Geologic Era
Time (In Millions of
Years Ago)
Geologic Events
Cenozoic
0 to 65 MYA
Thick glaciers in much of the world.
Rocky Mountains, Alps, and Himalayas form.
Glaciers cover North America.
Mesozoic
65 MYA to 248 MYA
Widespread volcanic activity
Age of dinosaurs
American, European, African continents move
apart.
Paleozoic
248 MYA to
544
MYA
Age of Ocean Life
Appalachian Mountains begin to form.
Warm shallow seas cover much of North
America.
Two ancient continents are found near the
equator.
Precambrian
544 MYA to 4600 MYA
Earth's first ice age occurs.
First sedimentary rocks form.
Oceans form.
Earth forms.
Earth’s Changing Surface
Strain in Rock
• Stress and Strain in Rock produce:
– Folding- deformation of rock
– Faulting- fracture of rock
Folding
• The process of deformation (changing form) that
alters the Earth’s surface
• Produces structures such as plateaus,
mountains and folds in the crust
• Related to volcanism and earthquakes
• Basic working theory is plate tectonics:
Pieces of the Earth’s lithosphere are in constant,
slow motion, driven by convection currents in the
mantle
The Earth’s Crust
• Oceanic: under the
• Continental: under the
ocean.
continents
– Thin, young and
– Thicker, older and
dense.
less dense
– Made primarily from
– Made primarily from
basalt
granite.
Plate Boundaries
• A fault is a break or
crack in the Earth’s
crust where the
plates sometimes
move past each
other, causing
earthquakes and
tremors.
Faulting
• Fault
– Produced by relative
movement on opposite
sides of a crack
– Footwall: mass of rock
below the fault
– Hanging wall: mass of rock
above the fault
– Fault plane: surface
between the footwall and
hanging wall
The Physics of Faults: STRESS
• 1. Tensional forces: stress that
pulls sections apart, normal
fault
• 2. Compression forces : two
sections of crust run into each
other, reverse fault
• 3. Transverse forces
(shearing): two sections sliding
sideways past each other, slipstrike fault
What kind of Fault?
Rock “Candy” Mountains
• Using different types of candy as a model we will
demonstrate how rocks in the earth’s crust can be
deformed by various forces to form mountains and
valleys.
• Three Forces:
– Tension- pulls apart
– Compression-squeezes together
– Transverse- slides by in opposite directions
• Rock reactions to forces:
– Faults and joints
– Folds (anticlines  synclines  )
The Tectonic Plates of the Earth
Types of Plate Motion
(see page 4. of Crustal deformation Lab)
The plates are all moving relative to each other. At the
boundary there is motion. Three possibilities:
• Spreading center: Divergent boundary
• Collision zone: Convergent boundary
– Cold lithosphere bends downward and begins sinking into the mantle
(subduction). Mountains are squeezed up here by the collision. Most
earthquakes occur here.
• Parallel plate motion: Transform boundary
– The San Andreas Fault is the most famous transform fault system.
Plate Movement
Oceanic - Oceanic Convergence - Example: Japan
At an ocean-ocean collision, one plate subducts beneath the
other, leaving a trace of the process in volcanoes and
earthquakes.
Oceanic - Continent Convergence - Example: Cascades
At an ocean-continent collision, the ocean subducts, and the continent
rides high. Volcanoes are built on the continental side due to melt which
comes off the subducting plate.
Continent - Continent Convergence –
Example: Himalayas
A continent-continent collision is like a train wreck - both sides end up
taking severe damage. Neither side wants to subduct. The entire
Alpine-Himalayan mountain system from Spain to Thailand is behaving
this way.
Mount Everest in the Himalaya Mountains
Nasa Web Page http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0202504.html
Continental Divergent Boundary
Example: Red Sea / E. African Rift
This image of the Sinai peninsula shows where the Red Sea spreading
center forks into two branches which can be seen as forming a brand-new
oceanic rift in the land.
Continental Transform Boundary - Example: San Andreas
What is a Volcano?
• Volcanoes are
openings in the
surface of the Earth.
Gas, ash, and magma
escape to cover the
surrounding land.
• Volcanoes can look
like a crack in the
ground or a coneshaped mountain.
3 Types of Volcanoes
• Shield
• Cinder cone
• Stratocone or
Composite
What’s the difference?
Shield Volcano
• Many layers of runny lava
• Flow piles up to form a mountain with
gentle slopes
Shield Volcano
Puu oo, Hawaii
How do you make a cinder cone?
• Made up of many layers of broken rocks
and ash.
• Wear away easily because there’s no
“glue” lava to hold it together.
• Wizard island found in Crater Lake in
Oregon is an example of a Cinder cone.
Crater Lake, Oregon
Cinder cone growing in
Crater Lake, Oregon
Cinder cone
Hawaii
Composite or Stratovolcano
• A stratovolcano is made of alternating
layers of ash and lava.
• The hardened lava is the “glue” that keeps
the layers from wearing away quickly.
• These are often very large volcanoes.
Examples are: Mt. St. Helens, Mt. Hood,
Mt. Shasta, and Mt. Adams.
Composite or Stratocone
Mt. St. Helen’s, Washington, USA
Shake it Up!
• An earthquake is caused by
energy waves passing
through Earth caused by a
sudden shift of Earth’s crust
along a fault.
What Do Mountains Have to
Do With Earthquakes?
• Earthquakes are a mountain building process.
• For example, The Appalachian Mountains were
formed when several volcanic island chains
collided with the North American Plate. The
collision generated high mountains.
• The Alps in Europe and Andes in South America
were also formed through collision.
Seismic Waves
• An earthquake produces vibrations called
seismic waves.
• Seismic waves are vibrations that travel
through earth carrying the energy released
during an earthquake.
• They move like the ripples created when
you drop a pebble in a pond.
3 Kinds of Waves
• There are three types
of seismic waves:
P waves, S waves, and
surface waves.
Primary Waves
• P waves are primary waves. They are the
first to arrive. P waves compress and
expand the ground like an accordion.
• Think about a slinky toy being pulled
straight out.
• P waves can move through liquids and
solids.
Secondary Waves
• After P waves come secondary waves or
S waves. S waves vibrate from side to
side and up and down.
• Think about the slinky again. Instead of
pulling it just out, think about pulling it out
and up and down.
• S waves shake structures violently. They
cannot move through liquids, only solids.
Surface Waves
• When P waves and S waves reach the
surface, some of them turn into surface
waves.
• Surface waves move more slowly than P
or S waves, but they produce more severe
ground movements. The ground can roll
like ocean waves. Other surface waves
shake buildings from side to side.
Picture Sources
• All pictures used were from copyright
friendly sites including:
•
•
•
•
Microsoft Word Clip Art
Pioneer.UEN.org
Pics4learning.com
NASA web Page
Text Sources
• Exline, Joseph D. Science Explorer: Earth’s Changing Surface.
(2002) Prentice Hall, Needham Mass., pp. 65-100.
• Field, N., Machlis, S., Discovering Volcanoes. (1993) Dog-Eared
Publications, Middleton, WI. Page 8.
• Vogel, Carole Garbuny. Science Explorer: Inside Earth. (2002)
Prentice Hall, Needham Mass., pp.58-65.
• Teacher resource book: State science core teacher text, grade 5.
(2002). Salt Lake City, UT: Utah State Office of Education/Jordan
School District.