Astronomy 100 -- Earth as a Planet

EARTH AS A PLANET
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Basic Properties of the Earth

1) How big is it?
A) Diameter = 1 Earth diameter.
B) Mass = 1 Earth mass.

2) How old it it?
4.6 billion years

3) Where is it?
1 Astronomical Unit (A.U.) from the Sun.
1 A.U. is defined as the distance from the Earth to the Sun.
8 Light-Minutes from the Sun.

4) What's it doing?
Rotation Period = 24 hours = 1 day.
Revolution Period = 365 days = 1 year.

THE EARTH'S INTERNAL STRUCTURE

A) CORE
Radius about 1/2 Earth radius.
Density of 11 grams/cc.
Mostly nickel and iron.
Center is solid and surrounded by molten layer.
This molten layer probably produces the Earth's magnetic field.

B) MANTLE
Outer half of Earth
Composition is volcanic rock

C) CRUST
About 15 km in thickness
Lower density rock [also oceans]

Fix Figure 8-15

This stratified structure implies the Earth has gone through a process known as DIFFERENTIATION. Just after it's formation, the Earth had to be MOLTEN in order for the high density material to sink to the CORE and the low density rock to "float" to the surface. Look at this Density Profile of the Earth

The Core-Mantle-Crust structure is a COMPOSITIONAL difference.

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PLATE TECTONICS

Interior layers are also distinguished by their RIGIDITY.

LITHOSPHERE -- Solid, rigid layer about 100 km thick.
[Crust and thin layer of the mantle]

AESTHENOSPHERE -- Soft, putty-like layer (100 km => 350 km).
[Partially melted mantle]

Plate Tectonics -- Process of crustal disruption due to the flow of material (aesthenosphere) under the crustal plates (lithosphere).
A Crustal Plate Map of the Earth

Fix Figure 8-20

Fix Figure 8-22

The flow of the putty-like aesthenosphere drags the plates in the lithosphere causing collisions between plates. These collisions occur in several different ways. See Fix Figure 8-21. While old plates are destroyed, new plate material is formed. This process resurfaces the Earth!

Examples:
1) Chain of Hawaiian Islands
2) San Andreas Fault. (Plates sliding against each other)
3) Andes Mountains (One plate going under another)
4) The Himalaya Mountain Range. (Two plates pushing upwards)

THE ATMOSPHERE OF THE EARTH

Nitrogen (80%) and Oxygen (20%)
(small amounts of carbon dioxide, water vapor, argon)

When the Earth formed, it possessed its PRIMEVAL atmosphere (mostly Hydrogen and Helium), which was heated and lost.
The present atmosphere is called the "SECONDARY" atmosphere.
Sources for the secondary atmosphere were:
1) volcanic outgassing
2) comets (source of water)
3) life (separates oxygen from the carbon dioxide)

Related Links of Interest
Earth From Space.
Earth Sciences Pictures.
The ABC's of Plate Tectonics.
Earthquakes and Plate Tectonics
The Dynamic Earth: The Story of Plate Tectonics .
Be sure to look at "Understanding plate motions".

Solar System Basics.
Our Moon in Detail.
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