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 HypothesisNebular  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 dust  About 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 protoplanets  Eventually, 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 gases 2.Low density 3.Are huge planets

Pluto —The First Dwarf Planet  Since 1930 until recently, Pluto has been known as the 9 th planet  However, it was unlike the gas giants  In 2006, astronomers changed the definition of planet and changed Pluto’s classification to a dwarf planet

The definition of a planet recently changed Planet qualifications  Must orbit the sun  Must have a basically round shape (hydrostatic equilibrium)  Must have cleared its orbit of other objects –Pluto misses the third—the Kuiper Beltthe 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 sank  Process 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 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 gravity  Blown 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% nitrogen  21% oxygen  1% 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