_01_EarthOrigin - GEL 1 Lecture 1 How Planets Form(Ch 1...

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1 GEL 1: Lecture 1 : How Planets Form (Ch. 1, specifically p. 23-30) Where did the Earth come from? How do planets form? Bottom line: Earth and the rest of the planets in our solar system formed from the remnant gas and dust left over from the formation of our star, the sun. Solar Nebula Hypothesis The solar nebula hypothesis proposes that the planets were formed from the disk of gas and dust that surrounded the sun as it formed. (i.e., planets form as a byproduct of star formation from nebula.) Nebula are clouds of gas and dust in space that mark the birthplace of stars ("star nurseries"). - the dust is a few atoms big and is composed of small amounts of various ices, oxides, carbon and some heavier elements such as iron. - the gas is almost entirely hydrogen (which you know as the simplest element, consisting of one proton and one electron). - hydrogen makes up about 75% of all the mass in the universe. Stages in the formation of the solar system (You just need to know the general ideas of this model, not the specifics.) - this process happens over tens to hundreds of millions of years . . . 1) Begin with a slowly spinning cloud of gas and dust ( solar nebula ) within the Milky Way galaxy. 2) The nebular cloud begins to collapse toward its rotating center under the influence of gravity. Centrifugal (outward directed) force causes the cloud to collapse to a central plane (this will eventually become the plane of the solar system.) 3) As the cloud collapses, gravity supplies the energy to heat up and compress the center, which eventually becomes the “protosun”. 4) The revolving masses of gas and dust became trapped in stable orbits around the protosun, forming lanes of concentration or “rings” 5) With increasing heat and pressure within the protosun, nuclear fusion occurs with the fusing of hydrogen into helium, releasing energy and stopping the contraction. Thus the protosun becomes the true sun.
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