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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 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 9th 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 Belt My very excellent mother just served us nine pizzas. nachos Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto Not shown to scale 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 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