Planet Earth

Chapter 17

Earth’s Interior and Plate Tectonics

17-1

Earth’s Interior• Earth is made up of three primary layers

each with its own unique composition and properties.

• The Crust - the solid, outermost and thinnest layer. It makes up only 1% of Earth’s volume. There are two types of crust.– Continental crust: thicker, exposed crust

• Deepest under mountains

– Oceanic crust: thinner and more dense than continental crust

Earth’s Interior• The Mantle - the thickest layer (80% of the volume of the

planet). It goes from solid to partially molten material called magma with depth. – The Lithosphere (lithos = “solid”) is made up of the crust and solid

part of the upper mantle.– The Asthenosphere (asthenos = “liquid”) is a layer of

partially melted, molten, rock that makes up the rest of the upper mantle just below the Lithosphere

– The lower mantle is mostly hot, liquid magma that extend down to the next layer

**It is the convection currents that occur in the Mantle that drive plate tectonics and continental drift.

Earth’s Interior• The Core is at the center of the Earth and has two

layers.– The outer core is very hot, liquid metals: mostly Iron (Fe)

and Nickel (Ni)– The inner core is also made of extremely hot metals

but because of the tremendous pressure, it remains solid.

• it spins within the liquid, metal outer core and generates Earth’s magnetic field that protects our planet from dangerous radiation from space.

Earth’s Layers

Plate Tectonics • Plate Tectonics and Continental Drift Theories

First started in the early 1900’s by German scientist Alfred Wegener.

– He proposed that all of the continents originated from one large supercontinent (Pangaea) and that they “drifted” to their present locations over a long time.

– He based his theory on the following observations:

• Continental margins (edges): – Similar in shape and size

– Fit together like “puzzle pieces”

Plate Tectonics • Rock types

– Rocks of Similar formation and age found on opposite continents

Plate Tectonics • Fossils of the same animals and plants found in these

rock layers, on different continents. (Mesosaurus)

Breakup of Pangaea

Exit Slip

• What are the three primary layers of earth? Describe each in detail.

• Where do convection currents occur?

• What is the difference between the theory of plate tectonics and continental drift?

Do Now

• What evidence was used to support the theory of plate tectonics? Describe in detail.

• Why wasn’t Wegener’s theory of continental drift widely accepted compared to the theory of plate tectonics?

Plate Tectonics • More discoveries in the twentieth century tell us that

Earth’s solid outer layer or crust (lithosphere) is broken into several large pieces called tectonic plates. – Tectonic plates ride on top of the softer, putty-like upper

mantle (asthenosphere).• they are moved by upwelling due to convection currents

in this soft, hot magma.

Plate Tectonics

• Tectonic plate boundaries occur at the margins (edges) of all these plates. There are three basic types of plate boundaries that form between two types of crust, continental and oceanic.

Plate Tectonics • Divergent boundaries: form where plates are pulling

apart, away from each other– Ocean to ocean: Sea floor spreading, Mid-Atlantic ridge– Continent to continent: African Rift Valley

Plate Tectonics • Convergent boundaries: form where plates are crashing

together– Ocean to continent: ocean crust subducts below the continental

crust • EX. West Coast of South America: Andes Mtns.

– Ocean to ocean: ocean crust subducts below another ocean crust.

• EX. Aleutian Islands/Indonesia/Japan

– Continent to continent: 2 continental crusts collide. • EX. The Himalayas/Rockies/Alps

Oceanic to Continental Convergence

Oceanic to Oceanic Convergence

Continental to Continental Convergence

Plate Tectonics • Transform fault boundaries: form where plates

grind past each other– Ocean to ocean: Lateral faults along the Mid-

Atlantic Ridge– Continent to continent: The San Andreas Fault (our

backyard)

• The entire landscape of our planet has been shaped by a combination of all these processes

Transform Fault Boundary

Exit Slip

• Compare and contrast transform plate boundaries, convergent plate boundaries, and divergent plate boundaries.

• What boundaries occur where oceanic and continental crust collide?

• What boundaries occur where oceanic and oceanic crust collide?

• What boundaries occur where continental crust collides with continental crust

Do Now

• What type of plate boundary would I expect an island to form at? What are the two types of crust involved?

• What type of plate boundary would I expect a mountain to form at? What are the two types of crust involved?

• What type of plate boundary would I expect a trench to form at? What are the two types of crust involved?

Earthquakes and Volcanoes

17-2

Earthquakes

• Earthquake – a sudden trembling of the Earth caused by a release of accumulated energy in the Lithosphere.– Most occur at tectonic plate boundaries– The point of rupture where the earthquake starts

underground is the focus.– The place on the surface directly above the focus is

the epicenter.

Earthquakes

Earthquakes

Earthquakes

• Seismic Waves – 3 types– P-waves (Primary waves)

• Compressional/Longitudinal waves that travel through Earth’s interior very fast

• they bend as they pass through the liquid outer core.

– S-waves (Secondary waves)• Transverse waves that travel through Earth’s interior

slightly slower that P-waves, and DO NOT travel through liquid

Earthquakes

Earthquakes• Surface Waves

– Slowest of the seismic waves and travel only at the surface. The most destructive of the three waves

Earthquakes

Earthquakes

• Seismic waves are recorded on a seismograph.

Earthquakes

• The amplitude of seismic waves is measured by the Richter Scale.

Earthquakes

• Damage or Intensity from an earthquake is measured in the Mercalli Scale.

Earthquakes

Will “The Big One” Happen Here?Will “The Big One” Happen Here?

Exit Slip

• Describe the three types of waves involved in an earthquake? Describe the motion and damage of each.

• What is the difference between a focus and the epicenter?

• What are earthquakes measured on?

Do Now• Describe the three types of waves involved in an

earthquake? Describe the motion and damage of each.

• What is the difference between a focus and the epicenter?

• What are earthquakes measured on?• What is the difference between the Richter scale and

the Mercalli scale?• Why are both scales necessary to use?• Is a seismograph the same as the Richter scale? Why

or Why not?

Volcanoes• Volcanoes – mountains formed through

repeated eruptions of lava and pyroclastics.

There are 4 main types of volcanoes.– Shield Volcanoes

• Very large and spread out

• Gentle Slopes and Gentle Eruptions• made from layers of lava• Example: Hawaii

Volcanoes

The Big Island of Hawaii

Volcanoes

• Composite or Strato Volcanoes– Very large and tall– Steep Slopes and Violent Eruptions because the

lava is thick, viscous and gaseous– made of alternating layers of lava and pyroclastics

(cinders)– Examples: Mt. St. Helens, Mt. Shasta, Mt. Fuji, Mt.

Vesuvius

Mt. Shasta

Mt. St. Helens before and after

Volcanoes

• Cinder Cones– small not very tall– moderate slopes and mild eruptions– made of pyroclastics (cinders and ash)– Examples: Pisgah Crater, Paricutín Mexico

Cinder Cone

Size Comparison

**Magma = molten rocks from the mantle+crust

Lava = magma that has reached the surface

Volcanoes

CalderasCalderasa. a. CalderasCalderas - large depressions in volcanoes. - large depressions in volcanoes.

c. Formed when volcano collapses inwardc. Formed when volcano collapses inward

after a after a catastrophic explosioncatastrophic explosion

b. Nearly circularb. Nearly circular

d. Size exceeds one mile in diameterd. Size exceeds one mile in diametere. Examples: Crater Lake , Yellowstone, Long e. Examples: Crater Lake , Yellowstone, Long

ValleyValley

Exit Slip

• What are the three different types volcanoes?

• Describe each type of volcano

• Provide one example of each type of volcano and describe why that example fits the type.

Do Now

• What is a caldera? Provide one example• What is a cinder cone volcano? What is

one example?• What is a shield volcano? Provide one

example.• List each type of volcano from least

explosive to most explosive

Minerals and Rocks

17-3

Minerals

• Minerals - the materials that make up rocks. A. There are about 3500 different minerals found in the Earth’s crust and only 20 of these make up 95% of all rocks.

Minerals

– All minerals share the following characteristics:• Naturally occurring, inorganic materials• Definite chemical composition (chemical formula).• Solids with a specific crystalline structure

.

Minerals

• There are nine common rock-forming minerals/mineral groups. Nearly all of these are silicates, meaning they consist of metal atoms combined with silicon and oxygen

Minerals• Nine most common rock-forming minerals or

mineral groups– Quartz (Silica): silicon dioxide, SiO2

– Feldspars: sodium or calcium aluminum silicates, NaAlSiO8 or CaAlSiO8

– Amphiboles: Complex hydrous silicates, (OH) containing calcium, magnesium, and iron

– Pyroxenes: Closely related to the Amphiboles

Minerals– Micas: Sheets of soft silicates with potassium (K+),

calcium (Ca 2+ ), or sodium (Na+) ions between the layers

– Chlorites: magnesium, iron-aluminum silicates; Mg6(AlSi3)O10 or Fe6(AlSi3)O10

– Calcite: Most common of the carbonate minerals, CaCO3

– Dolomite: Both a rock and mineral, MgCa(CO3)2

– Olivine: A magnesium or iron silicate colored various shades of green, Mg2SiO4, Fe2SiO4

Rocks

• A Rocks characteristics and appearance reflect it’s mineral composition and the way it was formed.– Rock can form in three different ways.

• Igneous rocks (“formed by fire”) formed when liquid magma solidifies.

– Two types » Extrusive (Volcanic): forms when magma erupts (lava) and

solidifies quickly at the surface.

Rocks

EXAMPLES: basalt, tuff, obsidian, pumice,

rhyolite, andesite

Rocks• Intrusive (Plutonic): form when large “bubbles” of magma

are trapped beneath the surface of the Earth (pluton); cools and solidifies slowly under pressure forming crystals.

EXAMPLES: granite, gabbro, diorite.

Rocks

Half Dome – a pluton above ground

Rocks• Sedimentary rocks Form when sediments, or small

pieces of weathered rock (clay, mud, sand, gravel, etc.) are deposited, compressed, and cemented together to form solid rock.

– The remains of living organisms can also be deposited along with these sediments forming fossils within the layers of these rocks.

– The type of sedimentary rock created depends on the sediments that formed it, and is named according to fragment size.

» EXAMPLES: mudstone, sandstone, limestone, coal, conglomerate

Sedimentary Rocks

Rocks• Metamorphic rock (“to change in form”) Forms when

older igneous, sedimentary, or other metamorphic rocks are changed due to extreme heat and/or pressure.

– Heat and pressure occurs in subduction zones– Heat occurs in volcanic vents: contact metamorphism

Pressure: occurs at convergent plate boundaries: forms fold mountains

Rocks• The Rock Cycle – the model that shows the origin of

the 3 rock types and their interrelatedness to each other

**The absolute age of a rock is determined by radioactive isotopes

**The Principle of Superposition is used to date rocks relatively

Exit Slip

• What are the different types of rocks?• Describe each rock type in detail.• What is the difference between igneous intrusive and

igneous extrusive rock?• What characteristic do all minerals share?• How many different types of minerals exist?• How many minerals make up most of Earth’s rocks?• list the nine most common rock forming mineral groups.

Do Now

• Describe the rock cycle in detail

Weathering, Erosion, and Deposition

17-4

Weathering, Erosion, and Deposition

VI. Weathering - a change in the physical form or chemical composition of rock materials exposed at the Earth’s surface.

A. Physical weathering - breaks rocks down into

smaller and smaller pieces and does not change the chemical composition. This occurs by the

following processes.

1. Water erosion

2. Frost wedging

3. Wind abrasion

4. Organic activities

5. Other physical forces

Weathering, Erosion, and Deposition

• Chemical weathering - when minerals in rocks react chemically to break down and change their chemical form.– Some minerals dissolve easily in water. Rain water is

slightly acidic (pH = 5.7) due to a natural reaction between water vapor H2O, and Carbon Dioxide CO2 , in the atmosphere. This forms a weak acid solution H2CO3 .

Weathering, Erosion, and Deposition

• EXAMPLE: The formation of Limestone caverns or sink holes. (See figure 17-29, pg.584).

• Acid rain - a severe form of this process caused by man-made pollutants.– Polluting gasses emitted during the burning of fossil fuels

(gasoline, coal, oil,) mix with water vapor in the atmosphere to form acid rain.

– These acids have a stronger pH than normal rain water and do a lot of damage to man-made and natural stone structures. (See figure 17-30, pg. 585).

Weathering, Erosion, and Deposition

• Erosion - the removal of weathered rock materials (sediments) and minerals by one or more of the following processes:– Moving water (most effective)

• Rivers or streams • Ocean currents, waves or tides

– Winds• Sand or dust storms

– Ice• Glaciers: massive, long lasting accumulations of compacted snow

and ice that moves down slope slowly• Frost Wedging

– Gravity• Land, rock, or mud slides

Weathering, Erosion, and Deposition

• Deposition - when the force in these moving processes slows or stops and the sediments are deposited (laid down) forming many different land forms:– Deltas and flats

– Beaches and sand bars – Sand dunes and hills– Moraines – Alluvial fans, rock piles and valleys

Exit Slip

• What is the difference between erosion, deposition, and weathering.

• Provide one example for each of the above.