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 are known 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.
What factors determine the rate at which weathering occurs?
Type of Rock
Climate
How do minerals in a rock affect the weathering?
a) Minerals that do not dissolve easily in water will weather slower
b) Minerals that do dissolve easily in water will weather faster
What is permeable?
Material is full of tiny, connected air spaces that allow water to seep through it
Why do permeable rocks weather chemically at a fast rate?
As water seeps through the spaces in the rock, it dissolves and removes material broken down by
weathering.
In what type of climate will chemical and mechanical weathering occur faster?
Wet Climate, Rainfall provides the water needed for chemical changes as well as for freezing and
thawing
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 erosion?
The process of carrying away (transporting) broken down rock and sediments
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 is the major agent of erosion that has shaped Earth’s land surface?
Moving water
What are the four main agents of erosion?
Water, wind, ice, & gravity
What is runoff?
Water that moves over Earth’s surface
What are the five main factors that runoff depends on?
Amount of rain
Type of soil
Vegetation
Shape of the land
How people use the land
What are three main features (landforms) formed by runoff and erosion?
Rills and Gullies
Tributaries
Streams and Rivers
What is a rill and gully?
 Rill is a tiny groove in the soil formed as runoff travels
 Gully is a larger groove in the soil (formed by several rills coming together) that carries runoff
after a rainstorm :
A gully will only contain water after it rains
What is a stream and river?
A stream is a channel along which water is continually flowing down a slope. It is formed by gullies
joining together. Small streams are also called creeks or brooks. As streams flow together, they form
larger and larger bodies of water called rivers.
What is a tributary?
A stream grows into a larger stream or river by receiving water from tributaries.
(A stream or river that flows into a larger river.)
What are 2 tributaries of the Mississippi River?
Ohio River and the Missouri River
What are four main land features formed by rivers and erosion?
Waterfalls
Oxbow Lake
Flood Plain
Meanders
What is a waterfall?
This may occur where a river meets an area of rock that is very hard and erodes slowly. The river flows
over this rock and then flows over softer rock downstream.
What is a floodplain?
The flat, wide area of land along a river. A river often covers its floodplain when it overflows it banks
during floods.
What is a meander?
A loop-like bend in the course of a river. As the river winds from side to side, it tends to erode the outer
bank and deposit sediment on the inner bank of a bend. Over time, the meander becomes more and
more curved.
What is an oxbow lake?
A special type of meander that has been cut off from the river. It may form when a river floods.