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Lecture3_2011.keyr -...

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Unformatted text preview: http://scrippseducation.ucsd.edu/faculty/driscoll/water Water on Earth Formation of Earth Origin of water Distribution of water Atmospheric circulation Water cycle Formation of the planets- Nebular hypothesis • ~4.6-4.7 Ga, As the nebula collapsed towards center of mass • Rotating disk shape to conserve angular momentum • Irregular patches or eddies coalesce into km-size (and less) planetesimals. • Planetesimals attracted each other and grew by accretion into protoplanets • Protoplanets continued to grow by collision of other protoplanets and planetesimals Planetary composition: The Nine Eight Planets • Inner terrestrial (Earth-like)planets • Compositional distribution akin to a distillationcondensation sequence Iron (Fe), Magnesium (Mg), Silicon (Si), & Oxygen (O) dominant • Mercury, Venus, Earth, Mars • Outer Jovian Planets (gas giants) • Hydrogen, helium, water (plus small iron cores) • Saturn, Jupiter, Neptune, Uranus Formation of Earth Formation of Earth Coalescence of silicate material. Cool. Then heating by: 1) meteorite impact 2) gravitational compression (potential energy) 3) decay of radioactive elements (not a lot of material, but packs a wallop). The heating caused the segregation of the Earth’s core, which concentrated iron. Caused melting or iron-nickel and formation of core. The ‘falling’ of this iron core would cause a heating increase of over 2000°C. Planetary differentiation is the most significant event in the history of the Earth. Caused ‘resetting’ of the planet. Differentiation of Earth . Originally a homogeneous agglomeration . Temperature more than enough to melt rocks o Collision/impact kinetic energy o Radioactive decay of: . Uranium (U) . Thorium (Th) . Potassium (K) Two times or ways to differentiate the Earth . Hot accretion (most likely) o High energy of impacts already melted & differentiated planetesimals or . Cold accretion o Melting & differentiation soon after accretion by radiogenic heat Introduction: Water Web— Connected Californians; TAPPING INTO A PLANETARY CYCLE: A Great Water Wheel; Vital Molecule; “Normal” Weather —Anything But “Average”; CALIFORNIA WATER LANDSCAPE: Pristine Waterscape; Groundwater; Hydrologic Regions: Compositional Structure (layering) o Developed because of density differences between compounds (not elements) o Core . Iron melting (iron catastrophe) by 4.5 Ga!! . Fe is ~1/3 mass of Earth . Sinking of molten iron releases potential energy (additional 2000˚ C of heat) . Formed Fe/Ni (+ S) core . Density = 11-12 g/cm3 The earth condensed in four basic steps. 1) It began to accrete from the nebular cloud as particles smashed into each other forming socalled planetesimals. 2) As the mass of the Earth grew so did it's gravitational force and the Earth began to compress itself into a smaller and denser body. This happened about 4.5 billion years ago. 3) In the third step the compression itself began to heat the interior of the Earth; also there was heat generated by radioactive decay. The interior of the earth began to melt. Because iron is the heaviest of the common elements that make up the Earth, as the Earth began to melt droplets of melted iron began to sink towards the center of the earth. 4) Proceeding slowly at first it sped up to catastrophic proportions hence it is called the iron catastrophe. Acidic rains interact with hot rocks o Mantle . Silicates (Si-O) . Enriched in Fe, Mg . Density = 3.3-7 g/cm3 o Crust . Silicates . Ca, Al, K, Na . Density = 2.6-3.1 g/cm3 Atmospheric Evolution • primordial gases, later lost from sun's radiation 2. exhalations from the molten surface (volcanic venting); bombardment from icy comets 3. steady additions of carbon dioxide, water vapor, carbon monoxide, nitrogen, hydrogen, hydrogen chloride, ammonia, and methane from volcanic activity 4. addition of oxygen by plant/bacterial life Origin of the Moon Origin of Moon 1. Early impact 2. Capture 3. Co-accretion Water vapor may also be very important ...
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