Formation of the Solar System

Chapter 27 page 684-

The solar system

consists of the sun, the planets and all of the other bodies that revolve around the sun

The Nebular Hypothesis

1796 French mathematician Pierre-Simon, marquise de Laplace

The sun and the planets condensed at about the same time out of a rotating cloud of gas and dust called a nebula

Solar Hypothesis

Matter is spread throughout the universe Some of it accretes, or comes together, in clouds

of gas and dustAbout 5 billion years ago, one of these clouds

began to be drawn together by gravity after it increased due to a nearby supernova or other forces

The rotating cloud of gas and dust is called a solar nebula

Accretion-matter is drawn together by gravity

The sun formed of gas in the middle of the rotating cloud

Planetesimals form from the collision of small bodies farther out

Planetesimals collide to form protoplanetsEventually, protoplanets become large and

form planets and their moons

Formation of Inner Planets

Were close to the sun with large percentages of heavy elements

Lost their gases because the gravity was not strong enough to hold them

When nuclear fusion began the remaining lighter elements were blown away from the blast

As cooling progressed, the heavier elements sank and layers formed

Today the inner planets are small, rocky and denser than outer planets

Formation of Outer Planets

Formed in the colder regions Did not lose their lighter elements At first their centers were heavy elements with

ice exteriors Now because of intense pressure, they have

layers of liquid gases Called gas giants because

1. Composed mostly of gases2. Low density3. Are huge planets

Pluto—The First Dwarf Planet

Since 1930 until recently, Pluto has been known as the 9th planet

However, it was unlike the gas giantsIn 2006, astronomers changed the

definition of planet and changed Pluto’s classification to a dwarf planet

The definition of a planet recently changed

Planet qualificationsMust orbit the sunMust have a basically round shape

(hydrostatic equilibrium)Must have cleared its orbit of other

objects

– Pluto misses the third—the Kuiper Belt

My very excellent mother just served us nine pizzas.

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto

Not shown to scale

nachos

Formation of Solid Earth

At first very hot 3 reasons

1. Heat from collisions with planetesimals

2. Weight of layers compressed and heated

3. Radioactive elements

Layers Form

Earth was hot enough to melt iron

Denser materials sankProcess called

differentiation

Present Earth

has a solid surface, but the interior is still hot enough to cause change i.e. plate tectonics

Formation of Earth‘s Atmosphere

The atmosphere formed because of differentiation

Less dense gas molecules like hydrogen and helium rose to the surface

Early atmosphere was H and He

These gases were so light they . .

Were not held by Earth’s gravityBlown away by the solar wind(There was not a fully developed magnetic

field )– It protects our present atmosphere

Outgassing from Volcanoes

Released large amounts of water vapor, carbon dioxide, nitrogen, methane, sulfur dioxide and ammonia

These gases reacted with radiation from the sun to form ozone that protects us from UV radiation

Present Atmosphere

Cyanobacteria and early green plants changed carbon dioxide into oxygen

About 2 by years ago the amount of oxygen increased rapidly

78% nitrogen21% oxygen1% other gases

Formation of Earth’s Oceans

Earth’s water may have come from space

Collisions with comets added water to the atmosphere

Other water came from volcanoes

When Earth cooled enough for water to condense, the oceans formed