Unit 1 january 17•The universe is about (~) 15 billion years (B.Y.) old.•Solar system is about 4.5 billion years oldoConsists of the sun and 9 planets circling it (figure 9.3)•2 groups of planets:oTerrestrial: small, rocky, denseMercury, Venus, Earth, MarsoJovian: large, gassy, lightJupiter, Saturn, Uranus, Neptune•Our solar system formed from relatively cold material. Formed from Nebula of gas and dust that undergoes accretion. Gravitational attraction- the larger a body the more dust and gas it pulls in—accretion (figure 1.2). Most of the material goes to form the sun, and the left over’s form planets, comets, and meteorites. •The earth warms up very rapidly due to:oAccretion- collisional heating oCompression- inner layers get heatedoDecay of radioactive materials inside earth—continues today•The earth becomes (partially) molten. This is caused (in part) by collision with mars’ sized body; this created the moon (figure 9.4). Then started to cool down. *rocks are very poor conductors of heat*once “crust” forms on the earth, inside still remains very hot—even today.•Earth may have been uniform in composition (inside and outside) at first, but because of heating, it became differentiated- layered (figure 1.5)•Once the temperature (T) inside is high enough, the earth begins to melt, “falls” to the center, and releases energy and causes more heating. Runaway process:lots of iron melt and falls to the center (figure 9.5)this is called The IronCatastrophe. •This huge heating event causes “boiling off” of volatiles from the inside. Water, other gasses belchedto the outside“The Big Burp”forms the early ocean and atmosphere (figure 9.6)oBoth are very different from what we have today. We look at layering in 2 different ways. Distances measured from surfaces of the earth…?•Earth is based on composition (figure 1.5)oCrust: solid rock (0-~40 km depth)oMantle: (different type of) solid rock (~40-2900 km depth)oOuter core: liquid iron (2900-5100 km depth)Inner core: solid iron (5100-6400km depth)-Based on Mechanical StrengthJanuary 19, 2007•Top layer: (0-100 km depth) lithosphere. Cool, strong, rocky(rigid), rocks much below melting point. Contains crust and part of the upper mantle•Next layer: (100-300 km depth) asthenosphere. Hot, weak (ductile bends). Rocks close to their melting point. Consistency of that like tar or silly putty.•Mesosphere: (300-2900 km depth) hot, strong, rigid, rocks under very high pressure. Not near melting
-Chemical Composition of the Earth•Top layer (crust)most studied and most accessible fig 1.7•Two elements (the big 2) make up 75% of total•In order: oxygen-O and silicon-S•These 2 with 6 others (the big 8) make up 99% of the crust. These are:Aluminum-Al, Iron-Fe, Magnesium-Mg, Calcium-Ca, Potassium-K, Sodium-Na•Contrast this with the composition of the whole earth. Most abundant in order:iron, oxygen, silicon, magnesium. Most of the Fe in the core. Most of Mg in themantle.