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Composition and Internal Structure of Earth

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Composition and Internal Structure of Earth Composition and Internal Structure of Earth Source: NASA Density of Earth Density = Mass/Volume What is the volume (or diameter) of the Earth? How much does the Earth weigh? Diameter of the Earth 7.2/360 = 787/C C=39,350 km (now 40,030 km) Diameter = 12,525 km (now 12,742 km) Alexandria 7.2º light rays from sun 7.2º Syene 1 Mass of the Earth Cavendish (1798) using Newton’s Laws Force = mass × acceleration (Newton’s 2nd Law) mEarth ×mbody F = mbody × g = G × r2 (Newton’s Law of Universal Gravitation) G is universal gravitation constant (6.672 × 10-11 m3kg-1s-2) g is acceleration due to gravity on earth, measured by timing how long it takes a mass to fall in a vacuum (9.8 ms-2) Mass of Earth = 5.9742 × 1024 kg Average Density of Earth Diameter of the Earth = 12,742 km (7,920 miles ) Mass of the Earth = 5.974 ××101024 kg (13.15 ×10× 1024 lb) Density = 5.5 g/cm3 Earth is actually not a perfect sphere: it is slightly oblate (squished) being fatter across the equator ( 12756 km diameter) than at the North and South Poles (12714 km diameter) Mean Atomic Wt of Planets Anderson and Kovach (1967)EPSL 2 Internal structures of terrestrial planets 1. Drilling the Earth! Well.. Only 1/3 of crust depth can be explored 2. Xenolith from Deep Earth (Mantle) :“Peridotite” (play video clip >>) 3 3. Seismic Data Analogy of Air/Water Play Animation>> Earth Interior W. W. Norton Seismic Data give strong evidence of Existence of Discrete Layers Int.Int.--C06abC06ab W. W. Norton 4 What about the deeper interior? Int.Int.--C.10aC.10a W. W. Norton … another evidence of liquid outer core Int.Int.--C.09C.09 W. W. Norton Another layer? ->-> Yes, Inner Core! 5 Compositional Terms Physical Property Terms (Butter!) (Liquid) Inner Core Outer Core Mantle (Liquid) Crust Chemical compositions Crust ->-> from rocks near the surface Mantle ->-> from mantle xenolith Core -->> from comparison with meteorite 6 Crust 1) Continental Crust – Thicker (~40 km) ––LowerLower Density – Mainly composed of Granite comp’ n 2) Oceanic Crust – Thinner (~7km) – Higher Density – Mainly composed of Basalt comp’n Mantle Lithosphere: Rigid Asthenosphere (~100- (~100-400400 km): less Rigid Upper (butter(butter--oror waxwax--like,like, semimoltensemimolten)) Mantle Transition Zone (~400 -700 km) Lower Mesosphere (below ~700 km) Mantle Compositional difference between Crust and Mantle is significant, but not as large as the difference with Core. Two types of high P rocks ––EclogiteEclogite – Peridotite Which one is the dominant rock type in mantle? – Needs to satisfy seismic data – Needs to satisfy petrologic data Peridotite is the dominant rock type 7 Core Composition? How do we know? Outer Core ––FeFe + Ni – Lower Density (compared to Inner Core) – Liquid ( in mo tio n) Inner Core ––FeFe + Ni – Higher Density – Solid Clue comes from Meteorite! It is believed that a certain type of meteorites has primordial chemical composition of the solar system. It is probably a valid assumption that the chemical composition of such meteorite is very similar to the composition of the Earth. Then, which element is enriched or depleted in the crust/mantle? Furthermore, what would be the composition of the Earth’s core? 8 / In Chondrite Fe2O3: 30% NiO: 2.1% Zn: 0.05% Cr: 0. 4% Major Core Constituents! Important Terms Refractory elements – High condensation T – Ca, Al, U, Ti, REEs Volatile elements – LdtiTLow condensation T ––K,K, Rb Incompatible Elements ((KdKd<< 1) – LILE (Large Ion Lithophile Element) K, RbRb,, Ce,Ce, Sr,Sr, Ba – HFSE (High Field Strength Element) ZrZr,, Nb,Nb, Hf,Hf, REEs, Th,Th, U, Ta What caused such layering? “Rain“Rain--OutOut Model” Need Energy!! (for this process + plate tectonicstectonics)) 9 Heat (Energy) Source #1: Bombardment 1. During the Early Stage of Solar System Formation 2. Primordial Process 3. Enough to melt the whole planet (Magma Ocean) 4. Earth and other Planets were very Hot! Heat (Energy) Source #2: Differentiation Sinking of FeFe--NiNi fraction to the center of the Earth (and other Planets) release gravitational potential energy During the Early Stage of Solar System Formation Primordial Process Heat (Energy) Source #3: Tidal Force When a body1 act on the gravity on body2, the gravitational field may not even on the body2 Distortion is commonly induced Internal Friction results in dissipation of its rotational kinetics into Heat 10 Heat (Energy) Source #4: Radioactive Decay Spontaneous changes (decay) in atomic nuclei – Parent: an unstable radioactive isotope – Daughter: the isotopes resulting from the decay of a parent Provides important info to Geologists ––(1)(1) age dating – (2) heat budget calculation Still occurring 11.
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