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
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
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
Scientists believe that the differentiation process only took a few million
After the heavier elements sank to the core, the earth’s mantle was able to
It was much like the skin that forms on hot pea soup
This thin layer became the earth’s crust
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
In these select places, scientists are able to directly observe the interior of
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
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.
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.
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
The first known seismograph was invented by the Chinese
It not only detected an earthquake, it was able to indicate the direction
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
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
The fastest of the waves is the P wave
They are also known as Primary waves
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
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
These characteristics of P waves and S waves are very important in
developing our understanding of the earth’s interior
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.
The spinning of the earth’s core, as was mentioned previously, causes a
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