# Introduction to Earth Science Key Ideas by moti

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```									Introduction to Earth Science – Key Ideas

Earth Science is the study of the Earth’s land, oceans, atmosphere and the universe in
which the Earth belongs to. The four main branches of earth science are:
· Geology- the study of Earth’s surface and interior.
· Astronomy- the study of the universe.
· Meteorology- the study of the Earth’s atmosphere and weather.
· Oceanography- the study of the oceans.

Earth is Spherical – The Earth is not flat or round, but it is an oblate spheroid. This means
that the Earth is slightly flattened at the poles, and it bulges slightly at the equator (Earth’s
equatorial circumference is greater than its polar circumference). This is caused by Earth’s
rotation (spin).

Early evidence that Earth is spherical:
--The mast of a ship is the first part to appear over the horizon when approaching port.
--Ships sailing north would see Polaris (north star) rise in the sky, and get lower as
they sailed south. Polaris is not visible in the southern hemisphere.
**The angle of Polaris above the horizon is your line of latitude!!
--During a lunar eclipse the edge of Earth’s shadow appears as an arc of a circle on
the moon’s surface.

**The force of gravity pulling down on us (toward the center of the Earth) causes us to have
weight. The farther we are from the center of the Earth, the less we weigh. Therefore, we
actually weigh more at the poles since we are slightly closer to Earth’s center. We weigh
slightly less at the equator!

Measuring Earth’s Circumference -

Eratosthenes’ Method (formula):

Earth’s Density – The density of an object is defined as the amount of material (mass) in
a given amount of space (volume). As you go deeper in the Earth, the mass of the rocks
above press down on the rocks below, decreasing their volume. This causes the rocks to
increase in density (Reference Tables).

Formula (Ref.Tables): Density = Mass / Volume (g/ml or g/cm³)

*Cutting an object into pieces, no matter how many, does not change its density! This is
true, because you are not changing what the object is made of!

Layers of the Solid Earth
It is believed that as the temperature of the newly formed Earth increased, iron and nickel
found in the rocks melted. The dense, heavy liquid iron and nickel flowed toward the center
of the Earth, melting the lighter rocks and forcing them toward the surface forming the
Earth’s layers. The layers are:
1. Inner Core- The Earth’s center made of solid iron and nickel.
2. Outer Core- A layer of liquid iron and nickel that surrounds the inner core.
3. Mantle- A thick layer of rocks above the outer core.
4. Crust- The upper most layer made up of lighter rocks. It is thickest below the continents

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