Earth Science Memory Work or Study Notes

Here's some memory work/study notes I used for the Earth Science class I taught last year:

Memory Work or Study Notes
for Earth Science

Layers of the Earth’s Core:

- see Lithosphere for details. The Crust is the outer surface of the earth on which we live. It includes the rocks, soil, sand, and water features of the surface of our earth.

Mantle - see info on each layer of the mantle listed under Lithosphere, Asthenosphere, and Mesosphere. The Mantle is the most substantial layer of the inner core of our earth. That is, it is the thickest, most substantial layer within the earth.

Lithosphere - This is the layer of the earth’s crust, plus the very outer part of the upper mantle. Here, the rock is rather cool (relatively) and brittle.

This layer is made up of six major and several minor tectonic plates that move around on the softer asthenosphere or the relatively plastic layer of the upper mantle of the earth on which the tectonic plates of the lithosphere move.

It is about 55 km (34 mi) thick beneath the oceans and up to about 200 km (124 mi) thick beneath the continents and is composed of rigid plates.

The high velocity with which seismic waves propagate through the lithosphere suggests that it is completely solid.

The movement of the plates of the lithosphere results in convergence, or collisions, that can form mountain belts and subduction zones, and divergence of the plates and the creation of new crust as material wells up from below separating plates. The lithosphere and asthenosphere are distinguished from the crust, mantle and core of the earth on the basis of their mechanical behavior and not their composition.

Asthenosphere - A zone beneath the earth’s surface that lies beneath the lithosphere and consists of several hundred kilometers of weak material that readily yields to persistent stresses.

Mesosphere - The layer of Mantle between the upper Mantle and Outer Core.

Outer Core - The central portion of the earth below the mantle, beginning at a depth of about 2,900 kilometers (1,800 miles) and probably consisting of iron and nickel. It is made up of a liquid outer core and a solid inner core.

The outer or upper zone of the earth's core, extends to a depth of 3160 miles (5100 kilometers), and includes the transition zone. It is the spinning of this layer that creates the magnetism of our poles.

Inner Core - The central part of the earth's core, extending from a depth of 3160 miles (5100 kilometers) to the center of the earth.

The outer and inner cores are also known as the siderosphere.

Dynamic Earth Theory - thin, fragile continental and oceanic plates slide very slowly on the mantle’s upper layers. Movement is produced by the convection currents in the mantle.

Plate Movements Result In:

Mountain Building
Production of New Crust
Destruction of Existing Crust

Twelve Main Plates:

North American
South American
Indian (might be one with Australia)

Smaller Plates:

Juan de Fuca

Some Scientists influencing the study of earth science:

Sir Francis Bacon - seventeenth century scientific thinker who was one of the first to discover from new mapping of the world that South America and Africa fit together like puzzle pieces. He helped promote interest in this idea for future scientists.

Alfred Wegener - first to introduce the theory of continental drift (that the continents have been moving slowly over most of geologic time) in 1912. He was instrumental in beginning the process of matching up fossil samples, magnetic crystals in rocks, rock layers, etc.

Harry Hess - American geologist who helped map the ocean floors during the 1960's, discovering the mid-Atlantic Ridge and other important seamounts, etc. He was instrumental in pinning down the scientific idea of how plates move through ocean floor spreading.

J. Tuzo Wilson - Canadian geologist who first came up with a complete theory of all processes occurring on the crust of the earth. He named this theory Plate Tectonics. This is one of the most important ideas in the history of science!

Andrija Mohorovicic - a geologist who discovered in 1909 that earthquake waves near the surface moved more slowly than waves passing through earth’s interior. He also noticed that p-waves passing through the earth did not move in a completely straight line, but were curved or deflected by something. He decided that the crust was less dense than the mantle because waves of all types move faster and straighter through denser, more solid objects. The boundary zone between the crust and mantle was named in his honor: The Moho Discontinuity.

Beno Gutenberg
- a German geologist who believed that the outer core must be made of liquid because slower s-waves could not pass through this layer, but seemed to bounce off it. The boundary zone between the mantle and outer core is named in his honor: The Gutenberg Discontinuity.

Three kinds of Plate Boundaries:

- two plates collide and either form mountains (piling up) or a subduction zone, with one moving over the other.

Divergent - two plates move away from each other and new crust is formed - as in the mid-ocean ridges.

Transform - two plates slide past each other, as in the San Andreas Fault.

Five Ways Mountains are Formed:

Volcanic Activity


Folding - rock put under pressure for long periods will fold like clay. Plates are pushed together like a roller coaster. Examples: the Appalachians, Rocky Mountains and Alps. The Appalachians are actually thought to be older than Gondwanaland. They are thought to have been formed when Africa and North America collided about 400 mya. They have now weathered down to a fraction of their former glory.

Faulting - fault lines are cracks in the earth’s crust. Sometimes plate collisions move whole blocks up vertically. Examples of fault-block mountains: Sierra Nevadas; Grand Tetons.

Dome Building - low mountains are formed from crust upheavals during collisions. Examples: The Black Hills and Adirondacks. These are also much higher than the surrounding landscape and are thus subject to very fast erosion.

What IS an earthquake?

An earthquake is a sudden, rapid shaking of the Earth caused by the release of energy stored in rocks.

About 90% of all Earthquakes are produced at plate boundaries where two plates are colliding, spreading apart, or sliding past each other. Earthquake waves resemble sound and water waves in the manor in which they move. They spread out from a starting point, or area of focus, in a ripple effect.

The focus is usually found far beneath the surface.

The point directly above the focus on the surface of the Earth is called the epicenter.

Compression waves
are one type of seismic wave. They are the first to arrive at the surface of the Earth. Because of this they are given another name, P or Primary waves.

P waves are the fastest of the seismic waves. They travel at incredible speeds, 14,000 m.p.h. at the surface to over 25,000 m.p.h. through the core of the Earth.  P waves are even able to pass all the way through the entire Earth.

Shear waves

S waves travel at about half the speed of P waves.
They move objects in their paths in an up and down motion in the direction that the wave is moving. S waves can only move through solids and because of this can travel only through the crust and mantle of the Earth. When S waves strike the outer core, which is made of liquid iron and nickel, the waves stop.

Surface waves are the third type of wave. These are the waves that produce the most destruction. They originate from the arrival of P and S waves at the surface. They are much slower than both P and S waves. Surface waves are limited to travel along only the surface of the Earth, just as waves in a body of water are limited to travel along only the surface of the water.

The Richter Magnitude is a number that is used to measure the size of an earthquake. The magnitude is a measure of the strength of the seismic waves that have been sent out from the focus.

A scientist uses a seismograph to determine the strength of the earthquake. A seismograph is an instrument that measures the amount of ground motion that an earthquake produces.

Each number on the Richter Scale represents an earthquake that is ten times as powerful as the number below it.

A tsunami is a large water wave that is formed by a volcanic eruption, underwater earthquake, landslide, or a hurricane. Tsunamis are the most dangerous of all the wave types. Tsunamis have the potential to reach heights of 120 feet (Krakatoa's eruption of 1883) and speeds of over 500 miles per hour.

When the wave is far out at sea it can go unnoticed because almost all of the wave stays under the surface of the ocean. When the waves reaches the shallow water of the coastline the height of the wave grows to its fullest and then crashes down on the land.

90% of all the continents and ocean basins are the product of volcanism. The air we breathe, and the water we drink have been produced by millions of years of eruptions of steam and other gases.

The term Volcano has two definitions:

An opening in the crust of the Earth in which molten rock called magma and gases can escape to the surface.


The mountain that is formed from volcanic eruptions.

Volcanoes are classified as active, dormant, and extinct.

Active volcanoes are either currently erupting or have erupted in recorded history. There are over 500 volcanoes on Earth that fit this category today.

Dormant or resting volcanoes are not currently erupting but are considered likely to do so. Mt. St. Helens had been dormant for one hundred twenty-three years before it erupted in 1980.

Extinct or dead volcanoes have not erupted in recorded history and are not expected to erupt again.

A lava dome is a steep mass of very thick and pasty lava that is pushed up from the main vent. The lava is so viscous (thick and pasty) that it does not flow but slowly rises higher with each movement of magma in the conduit. Think of toothpaste that is slowly squeezed and then stopped and then squeezed again from the tube. This is how the lava dome in Mt. St. Helen's was formed.

Volcanoes form in three areas of the earth:

Subduction zone volcanoes are the most violent and destructive of the volcanic types. Mt. St. Helens, Mt. Pinatubo, Krakatoa, and Mt. Vesuvius are all famous explosive subduction zone volcanoes.

Mid-ocean rift volcanoes form where two oceanic plates are spreading apart. There are more rift zone volcanoes than any other type.

The third place that volcanoes form occurs at a Hot Spot.

Many volcanoes erupt in very consistant patterns, while other volcanoes have no eruption pattern at all. This makes forecasting eruptions difficult.

What makes predicting eruptions even more difficult is the fact that many volcanoes start with one type of eruption pattern and then change eruption patterns as they grow older.

Some of the most powerful eruptions in recorded time have come from volcanoes that have been dormant for hundreds and even thousands of years.

Some volcanoes produce little or no lava.

Some volcanoes eject pyroclasts, which are fragmented or broken rock.
The word pyroclastic comes from a Greek word that means "Rock broken by fire".

When volcanoes do produce lava flows they are classified as either Pahoehoe or Aa. The lava is identical in both pahoehoe and aa lava flows, the difference comes from the amount of lava erupted and the speed of cooling.

Pahoehoe lava flows are produced from a small amount of lava that moves slowly, while aa flows usually are associated with a large volume of lava that moves swiftly.

Aa flows are generally 6-15 feet thick and pahoehoe flows are usually 1-3 feet thick.

If the lava is very hot and has a low viscosity (runny with a low gas and silica content) the lava flow is called Pahoehoe. Pahoehoe (Pa-Hoy-Hoy) lava flows are very hot, thin and runny. When it cools is has a smooth to ropey texture because of the low silica content which makes it cool quickly.

Pahoehoe flows creep along generally at less than 3 feet per minute but some flows have been measured at over 20 miles per hour. The flow advances in globs of lava. These globs of lava are called lobes.

If the lava has a high viscosity (thick and pasty with a high gas and silica content) it is called Aa. Aa lava flows are formed when the lava is produced in a manner that allows it to cool quickly.

Pyroclasts are particles that are ejected during a volcanic eruption. They range in size from very small particles called dust to ash (1/10 of an inch) to lapilli ("little stones" 1/10 of an inch to 2 inches ) to the largest of the pyroclasts, blocks and bombs (2 inches to many feet in diameter).

Volcanic Ash is any very fine grained material erupted from a volcano that is less than 1/10 of an inch (2 millimeters) in diameter. This is very fine material and was given the name ash because it resembles ashes from the burning of wood or coal.

Volcanic ash is rock that has been exploded and shattered by steam inside the volcano. Ash and lava flows build stratovolcanoes into mountains with repeated eruptions.

Pyroclastic flows are spinning mixtures of pyroclasts (small pieces of obsidian, ash, pumice, and cinders) and very hot gases. They flow down the side of the volcano at speeds up to 100 miles per hour and at temperatures sometimes over 700 degrees Fahrenheit!! With temperatures that high, pyroclastic flows kill everything it their path.

Pumice is a very light colored, frothy volcanic rock. Pumice is formed from lava that is full of gas. The lava is ejected and shot through the air during an eruption. As the lava hurtles through the air it cools and the gases escape leaving the rock full of holes.

Pumice is so light that it actually floats on water. Huge pumice blocks have been seen floating on the ocean after large eruptions. Some lava blocks are large enough to carry small animals.

Bombs and blocks are the largest of the pyroclasts.

Blocks are angular chunks of rock that has been ejected from a volcano during an eruption. A bomb is formed as lava hurtles through the air, cooling and forming a hardened lava rock. A bomb's shape is usually more rounded or streamlined.

Obsidian is a very shiny natural volcanic glass. When obsidian breaks it fractures with a distinct conchoidal fracture. Obsidian is produced when lava cools very quickly. The lava cools so quickly that no crystals can form.
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