Earths Structure and Processes

Study Guide

Learning Target #1

Explain and understand characteristics of the 3 layers of the Earth

a) Explain that the Rock cycle is a closed system on Earth

b) Compare/contrast the change of properties of rocks as they pass from one

phase to another

Igneous, Sedimentary, & Metamorphic

What are the three main layers of Earth?

1.  Crust

2.  Mantle

3.  Core

What is the crust? (The first layer of Earth)

A layer of rock that forms Earth’s outer skin

A layer of solid rock that includes both dry land and the ocean floor

What are the two distinct parts of the Earth’s crust?

The heavy, basaltic oceanic crust

The lighter, granite based continental crust

How thick is Earth’s crust?

Some places – between 5 – 40 kilometers thick

It can be up to 70 kilometers thick beneath mountains

What is the oceanic crust?

The crust beneath the ocean that consists mostly of rocks such as Basalt

Around 10 kilometers thick (about 6 miles) on average

What kind of rock is basalt?

A dark rock with a fine texture

Why is the oceanic crust, never older than around 200 million years?

The forces of plate tectonics cause the crust to continually be renewed

What is the continental crust?

The crust that forms the continents that consists mainly of rocks such as granite

It is over three billion years old in places

Its thickness varies between 40 and 70 kilometers (25 and 43 miles)

What kind of rock is granite?

A rock that is usually a light color and has a coarse texture

Why does the continental crust “float” on the underlying mantle?

The average density is lower than that for the oceanic crust, allowing it to float on the underlying mantle, pushed along by the spread of the ocean floors and creating the continental drift

What is the mantle? (The second layer of Earth)

A layer of rock that is very hot, but solid

The mantle is divided into 3 layers based on physical characteristics of those layers

The mantle is nearly 3,000 kilometers thick

What is Earth’s core? (The third layer of Earth)

It is made mostly of the metals iron and nickel.

It consists of 2 parts: a liquid outer core and a solid inner core

Together, the inner and outer core are 3,486 kilometers thick

What is the rock cycle?

a)  The rock cycle is the natural process in which rocks transform from one rock type into another rock type over time, a type of natural recycling.

b)  The rock cycle is largely driven by lithospheric plate movements which cause subduction and uplift, also by climatic conditions of weathering, erosion, and deposition.

c)  Plate movements start the rock cycle

Explain the rock cycle

1.  Igneous rocks are exposed to weathering and erosion, the remains are deposited to a new location (deposition).

2.  Here they form into sedimentary rocks through lithification. Igneous and sedimentary rocks can also be changed by heat and/or pressure into metamorphic rock.

3.  If these metamorphic rocks are melted, then solidify, they become igneous rocks, and the cycle starts all over again.

What are the two main factors in the mantle that contribute to the rock cycle?

Pressure and heat

What are the 3 types of rock found on Earth?

Igneous

Sedimentary

Metamorphic

What is lithification?

Lithification is how solid rocks are formed (cementation and compaction. When sediments are exposed to extreme amount of pressure over a period of time, they are then formed into solid rocks.

What are characteristics of igneous rocks?

Any rock that is formed from magma or lava

These rocks are classified according to origin, texture, and mineral composition

May form on or beneath Earth’s surface

Hard, dense, and durable

What is extrusive igneous rock?

Rock formed from lava that erupted onto Earth’s surface

What is the most common extrusive rock?

Basalt

What is intrusive igneous rock?

Rock formed when magma hardened beneath Earth’s surface

How are igneous rocks classified by texture?

Texture depends on the size and shape of its mineral crystals

Texture depends on whether the rock is intrusive or extrusive

How are sedimentary rocks formed?

Formed through a series of processes: erosion, deposition, compaction, and cementation

Erosion – particles carried away by water or wind

Deposition – particles deposited as loosely packed sediment

Compaction – buried, particles squeezed together under great pressure

Cementation – buried, particles glued together as mineral solutions harden

What are characteristics of sedimentary rocks?

Three major groups: clastic rocks, organic rocks, and chemical rocks

What is a clastic sedimentary rock?

Forms when rock fragments are squeezed together

What is an organic sedimentary rock?

The rock forms from the remains of plants and animals that are deposited in thick layers.

What is a chemical sedimentary rock?

When minerals that dissolve in a solution crystallize

What are characteristics of metamorphic rocks?

Formed by heat and pressure deep beneath Earth’s surface

It can form from igneous, sedimentary, or other metamorphic rocks

What are different types of metamorphic rocks?

Foliated Rocks – grains arranged in parallel layers or bands

Nonfoliated Rocks – mineral grains are arranged randomly

Learning Target #2

Explain how landforms are shaped/formed as a result of constructive forces.

Constructive Forces: Crustal deformation, faulting, volcanic eruption, deposition of sediment

What destructive & constructive processes act together in a cycle that wears down and builds up Earth’s surface?

Weathering, erosion, and deposition (constructive)

What is deposition?

This occurs where the agents of erosion lay down (deposit) sediment

Explain how erosion and deposition work together in changing Earth’ surface?

Over millions of years erosion has gradually wore away mountains. The sediment had to go somewhere else, therefore the valleys along the mountains began to build up from the deposition.

·  Erosion causes a surface to wear away, but deposition puts those materials lost somewhere else, causing another area to build up.

What features are created by deposition and erosion working together?

Alluvial fans

Deltas

Add soil to a river’s flood plain

What is an alluvial fan?

A wide, sloping deposit of sediment formed where a stream leaves a mountain range shaped like a fan

What is a delta?

Sediment deposited where a river flows into an ocean or lake builds up a landform. It can be a variety of shapes (arc or triangle).

What is crustal deformation as a constructive force?

·  As a result of continental movement, the Earth’s surface near active faults deforms before, during, and after earthquakes

·  The ground surface near active volcanoes also deforms as a consequence of eruptions and volcano evolution

Why are there 7 continents on Earth?

Movement of tectonic plates has reconstructed the original continent by breaking it into several pieces, like a jigsaw puzzle

What was the original (one) continent called on Earth?

Pangea

What is an earthquake?

An earthquake is the shaking and trembling that results from the movement of rock beneath Earth’s surface.

What causes earthquakes?

The forces of plate movement

Plate movements produce stress in Earth’s crust, adding energy to rock and forming faults

Where do most earthquakes begin?

Most begin in the lithosphere within about 100 km of Earth’s surface

What is an earthquake’s focus?

The area beneath Earth’s surface where rock that is under stress breaks, triggering an earthquake

What is an earthquake’s epicenter?

The point on the surface directly above the focus

What is faulting?

·  Rocks are very slowly, but continuously moving and changing shape. Under high temperature and pressure conditions common deep within Earth, rocks can bend and flow.

·  In the cooler parts of Earth, rocks are colder and brittle and respond to large stresses by fracturing.

Earthquakes are the results of brittle rock failure.

What is a fault?

A fault is a crack across which the rocks have been offset.

·  They range in size from micrometers to thousands of kilometers in length and tens of kilometers in depth, but they are generally much thinner than they are long or deep.

How do volcanic eruptions cause crustal deformation?

Volcanic eruptions affect the ground surface near active volcanoes

·  The lava from a volcano builds up rock (igneous) on Earth’s surface

How many volcanoes are on Earth?

·  The exact number of volcanoes is unknown. There are probably millions of volcanoes that have been active during the whole lifespan of the earth.

·  During the past 10,000 years, there are about 1500 volcanoes on land that areknown to have have been active, while the even larger number of submarine volcanoes is unknown.

·  At present, there are about 600 volcanoes that have had known eruptions during recorded history, while about 50-70 volcanoes are active (erupting) each year.

·  At any given time, there is an average of about 20 volcanoes that are erupting.

Which volcano is the biggest volcano?

The biggest volcano in the world is Mauna Loa, in Hawaii.

·  It rises off the seafloor to 13,000 feet above sea level.

How are underwater volcanoes different from volcanoes that are above sea level?
Submarine volcanoes are very different from the volcanoes that are above sea level.

·  Water has a higher pressure than air. This higher pressure can cause an underwater, explosive volcanic eruption.

·  One famous example of an underwater explosive eruption is Surtsey, a new volcano off the south shore of Iceland. When Surtsey erupted it punched through the sea and became an island!

How many volcanoes are there in the United States?
The lower 48 states in the U.S. have about 40 volcanoes that we think have had very recent activity, so they must be considered as active volcanoes.

·  In Alaska, the number is more like 60. When we talk about whether a volcano is active or potentially a threat, it is important to look at the past ten years.

·  Most of the important eruptions and disasters have happened at mountains that were not even recognized as being volcanoes, for example Pinatubo (Philippines, 1991), El Chichon (Mexico, 1982), Arenal (Costa Rica, 1968).

Are there any volcanoes in the U.S. that are threatening at this time?
The most important volcano in the U.S. is probably Rainier, which is not showing signs of activity but has produced very large eruptions.

·  The danger is many people live close to Rainier.

Is it true that there are volcanoes in the ocean?
On the surface of the earth, we know of at least 1,500 active volcanoes.

·  Scientists estimate the ocean contains 10,000 volcanoes! We just don't have much chance to see them because they are hidden away!

What landforms result from volcanoes?

Volcanic Islands & Crater Lakes

What landforms result from earthquakes?

Mountains

What landforms result from deposition?

Deltas & Peninsulas

Learning Target #3

Explain how landforms are shaped/formed as a result of destructive forces.

Destructive Forces: Weathering & Erosion

What is weathering?

The process of breaking down rock and other sediments through mechanical or chemical causes

The process that breaks down rock and other substances at Earth’s surface

What factors contribute to weathering?

Heat, cold, water, ice, and oxygen and carbon dioxide in the atmosphere

Examples:

a)  Repeated freezing and thawing can crack rock apart into smaller pieces

b)  Rainwater can dissolve minerals that bind rock together

c)  Weathering can cause bicycles to rust, paint to peel, side-walks to crack, and potholes to form

What are 2 types of weathering?

Mechanical Weathering

Chemical Weathering

What is mechanical weathering?

Rock is physically broken into smaller pieces

What are characteristics of mechanical weathering?

a)  It works slowly

b)  Over long periods of time, mechanical weathering can break down whole mountains

What causes mechanical weathering?

a)  Freezing and thawing – example: ice wedging

b)  Release of pressure – erosion removes material from rock to reduce the amount of pressure

c)  Plant growth – roots enter cracks in rocks and force it to split

d)  Actions of animals – burrowing animals loosen and break apart rocks in the soil

e)  Abrasion – grinding away of rock by rock particles carried by water, ice, wind, or gravity

Why are the Appalachian Mountains so small in height, even though they are amongst the oldest mountains in the world?

Weathering and erosion have had longer to wear them down

What is the most important force of mechanical weathering in a cool climate?

freezing and thawing of water.

How does ice wedging weather rock?

Water seeps into the cracks of a rock and then freezes. Freezing causes the water to expand, therefore acting like a wedge.

What is chemical weathering?

The process that breaks down rock through chemical changes

What causes chemical weathering?

a)  Water – breaks down minerals in rock by dissolving it

b)  Oxygen – oxygen mixed with rain causes oxidation (rust)

c)  Carbon dioxide – it dissolves in rain water (weak acid)

d)  Living Organisms – as plants roots grow, they produce weak acids that slowly dissolve rock around the roots

e)  Acid Rain – polluting air with sulfer, carbon, and nitrogen compounds create acid rain

What is the most important cause of chemical weathering?

Water

How does water weather rock?

It does so by dissolving it. When a rock or other substance dissolves in water, it mixes uniformly throughout the water to make a solution.

What is oxidation?

Iron combines with oxygen in the presence of water

What can happen as a result of oxidation?

Rust

Examples:

Bicycle or metal tool left in rain – it will begin to rust

Rock that contains iron will also rust – Rust makes rock soft and crumbly and gives it a red or brown color

How does carbon dioxide cause chemical weathering?

It dissolves in rainwater creating a weak acid called carbonic acid that easily weathers rocks like marble and limestone

What does man do to cause acid rain?

Burning large amounts of coal, oil, and gas for energy

How does the burning of coal, oil, and gas cause acid rain?

They pollute the air with sulfur, carbon, and nitrogen compounds that react chemically with the water vapor in the clouds forming acids.