Chapter 4:Energy from below

The Earth’s Interior

Accretion describes how the earth built its mass.

Billions of years of rubble crashing into the earth gradually built up a sufficient mass to create a gravitational field.

Then the pressure and the kinetic energy of the smashing rocks began the chemical chain of events that led to the development of the earth’s layered surface.

The decay of radioactive elements

Differentiation was able to occur due to the intense heat caused by the kinetic energy and the pressure.

Heavier elements sank to the center where the intense pressure kept it in a molten state.

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While the earth’s interior should be in a liquid state due to the intense heat and pressure, that same pressure keeps the interior acting like a semi-solid

The earth’s inner core is made up of the densest elements like iron

This material is spinning within a coat of less dense elements.

The spinning action generates a magnetic field.

It acts much like a car generator.

The spinning creates a force field

This force field protects the earth from the solar winds.

A compass uses this

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Chapter 4—the layered earth

Scientists believe that the differentiation process only took a few million years

After the heavier elements sank to the core, the earth’s mantle was able to solidify

It was much like the skin that forms on hot pea soup

This thin layer became the earth’s crust

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Due to the different densities of the layers of the earth, the tend to “float” around each other.

The thin layer known as the crust is composed of two main types;

The ocean crust and the surface crust

Evidence of the earth’s interior comes from two main sources

First: indirect evidence

Scientists study meteorites and extra-terrestrial bodies to develop hypotheses about the earth’s interior

This is because it is difficult to see deep into the earth

Second: direct evidence

There exist a small number of places on the earth where the earth’s crust has been thrust up allowing them to be directly observed

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In these select places, scientists are able to directly observe the interior of the earth

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The best source of indirect evidence comes from meteorites.

These small fragments of larger bodies strike the earth and allow scientist to observe the reaction

Due to the law of uniformitarianism they can then hypothesize about the continuation of such action.

Meteorites are meteors until they come in contact with the earth’s surface

They are divided into three main types:

Stony meteorites. These have a composition similar to that of the earth’s mantle allowing us to observe the reaction of their striking the earth and releasing their chemicals

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Stony iron meteorites have a complex composition

Scientists believe that these are the source of much of our core material and helped the chemical reactions needed for the heat process.

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The last category are the iron-nickel meteorites.

These are the densest of the meteorites and provide valuable clues to the development of the earth’s core.

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The study of earthquakes is called seismology

Seismologists will study the waves that earthquakes emit

Ever wonder how animals are able to “sense” an impending earthquake?

When the earth is about to undergo a seismic event, waves are sent out

Similar to a shock wave these waves can be detected by highly sophisticated instruments.

The first known seismograph was invented by the Chinese

It not only detected an earthquake, it was able to indicate the direction

Chapter 4--Seismology

Earthquakes are caused by the movement of the tectonic plates

These plates “float” on the aesthenosphere

There are different types of earthquakes and plate boundaries

The main point of the earthquake’s origin is the focus

The part directly above the focus, the part that occurs on the surface of the earth, is the epicenter

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As was mentioned before, earthquakes emit high frequency “waves”

The military is often a great benefactor to earth sciences.

At the dawn of the atomic age, the military needed a way to detect the atomic explosions caused by rival countries.

The military developed detection devices that were capable of reading the types of waves cast by the explosion of a nuclear device.

They discovered that there were three types of waves produced by earthquakes.

The fastest of the waves is the P wave

They are also known as Primary waves

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P waves travel through a series of compression and dilation actions.

So, P waves—Push and Pull

By doing this they travel very fast as they must be in immediate contact with the next rock in order to travel

P waves are also known as compressional waves

P waves can travel through liquid as liquids have the ability to transmit compression waves

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S waves are known as Secondary waves

These waves are slower and travel by moving side to side

S waves can only travel through solids as they need a hard object to transmit the energy

These characteristics of P waves and S waves are very important in developing our understanding of the earth’s interior

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Look at the diagram on page 62

Here one can see how scientists were able to map out the density of the interior of the earth using these waves.

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The spinning of the earth’s core, as was mentioned previously, causes a generator effect.

This generates a magnetic field that encompasses the earth and protects it from the dangerous effects of the solar winds

It has been hypothesized that Mars once held an atmosphere similar to earth

The ceasing of its interior engine caused the solar winds to sweep away the atmosphere like a giant broom

Today, Mars is a dead planet

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