Geologic TimeGeologic 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 TimelineGeologic 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 SurfaceEarth’s Changing Surface

Strain in RockStrain in Rock

• Stress and Strain in Rock produce:– Folding- deformation of rock– Faulting- fracture of rock

FoldingFolding

• 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 CrustThe Earth’s Crust

Plate BoundariesPlate 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 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: STRESSThe 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, slip-strike fault

What kind of Fault?What kind of Fault?

Rock “Candy” MountainsRock “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 EarthThe Tectonic Plates of the Earth

Types of Plate MotionTypes of Plate Motion(see page 4. of Crustal deformation Lab)(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 MountainsMount Everest in the Himalaya MountainsNasa Web Page http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0202504.htmlNasa Web Page http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0202504.html

Continental Divergent BoundaryExample: 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?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 cone-shaped mountain.

3 Types of Volcanoes3 Types of Volcanoes

• Shield

• Cinder cone

• Stratocone or

Composite

What’s the difference?What’s the difference?

Shield Volcano

• Many layers of runny lava

• Flow piles up to form a mountain with gentle slopes

Shield VolcanoShield VolcanoPuu oo, HawaiiPuu oo, Hawaii

How do you make a cinder cone?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, OregonCrater Lake, Oregon

Cinder cone growing in Cinder cone growing in Crater Lake, OregonCrater Lake, Oregon

Cinder coneCinder coneHawaiiHawaii

Composite or StratovolcanoComposite 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 StratoconeComposite or StratoconeMt. St. Helen’s, Washington, USAMt. St. Helen’s, Washington, USA

Shake it Up!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 What Do Mountains Have to Do With Earthquakes?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 WavesSeismic 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 Waves3 Kinds of Waves

• There are three types of seismic waves:

P waves, S waves, and surface waves.

Primary WavesPrimary 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 WavesSecondary 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 WavesSurface 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 SourcesPicture Sources

• All pictures used were from copyright friendly sites including:

• Microsoft Word Clip Art

• Pioneer.UEN.org

• Pics4learning.com

• NASA web Page

Text SourcesText 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.