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GEOL 150 Earth Revealed - Winter 2014

Instructor: Kim Bishop

Office: La Kretz Hall Rm 116

Phone: (323) 343-2409

email: kbishop@calstatela.edu

Origin of the Earth and Solar System 

What is the Solar System?Solar System

• Sun

• Planets

• Moons

• Asteroids

• Meteors

• Comets

Our Solar System is defined as our Sun and the variousobjects that orbit around the Sun.

Our Sun at the center of the Solar System is one star

of billions that make up the Milky Way galaxy. A

galaxy is a huge, disk-shaped, rotating mass of

billions of stars.

The Milky Way galaxy is one of billions of galaxies that

exist within the Universe.

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There are important characteristics of the Solar

System that need to be accounted for in a reasonable

hypothesis for the origin of the Solar System

What are these characteristics?

1) The planets and other objects orbit the sun in

approximately the same plane.

2) The planets and other objects orbit the sun in

the same direction.3) The planets revolve around their axes in the

same direction as they orbit the sun

4) The 4 inner planets (Mercury, Venus, Earth,

and Mars) are small and “rocky” compared to the

4 outer planets (Jupiter, Saturn, Venus, &

 Neptune), which are large and gaseous.

Note that Pluto is now

considered a “dwarf

planet”, not a planet. 

Important Characteristics of the Solar System that need to be

accounted for in a reasonable hypothesis for the origin of the

Solar System

1) The planets and other objects orbit the sun inapproximately the same plane.

2) The planets and other objects orbit the sun in the same

direction.

3) The planets revolve around their axes in the same

direction as they orbit the sun.

4) The 4 inner planets (Mercury, Venus, Earth, and Mars)

are smaller and “rocky” than the 4 outer planets (Jupiter,

Saturn, Venus, & Neptune), which are large and gaseous.

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The most widely accepted hypothesis for the origin of the

Solar System is referred to as the Nebular HypothesisAccording to this theory, the solar system began as

a huge cloud of slowly rotating gas and dust,

known as a nebula.

Many nebulas are present in the universe and are

recognized as having resulted from the explosion of a

star. Slowly, the nebula that formed our Solar System

began to contract because of gravity

As the nebula contracted, it began to rotate faster. This

caused the cloud to flatten into a disk-like shape.

Most of the mass collapsed into the center.

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Eventually, the Sun developed in the center of the disk. The

sun was sufficiently massive that the process of nuclear fusion

began. Because of fusion, the Sun emits radiation (some of

which is light), along with charged particles - protons and

electrons.

This emanation of rapidly moving charged particles from theSun is known as the solar wind.

Collision of the solar wind particles with the particles away

from the sun blew the lighter elements, mostly hydrogen and

helium, in the disk away from the sun.

The heavier elements were too heavy to be blown outward.

Because most of the elements in the cloud orbiting the sun

were lighter (Hydrogen and Helium), most of the material thatwas closer to the Sun was blown outward.

In time, the particles orbiting the sun were attracted

to one another because of gravity and they began to

coalesce (come together). Eventually, the growing

bodies became the planets and other features of the

Solar System.

The heavier elements, which were closer to the Sun,

formed the 4 rocky inner planets, whereas the lighter

elements formed the 4 icy and gaseous outer planets.

How old is the Solar System?

There is strong evidence that the Solar System formed

4.5 billion years ago.

Scientists refer to this concept for the

origin of the solar system as the

Nebular Hypothesis

Artist depiction of early Earth forming from collisions

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Don’t confuse the “Nebular

Hypothesis” with the “Big Bang

Theory” 

The Nebular Hypothesis explains the origin of the Solar

System 

The “Big Bang Theory” explains the origin of the

Universe. Evidence indicates the universe began 13.7

billion years ago.

The universe includes everything that we know that exists. This

means not only our Sun, but all of the stars in the sky.