Early History of Terrestrial Planets
Early History of Terrestrial Planets GEOL 101 001
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GEOL 101 001
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This 4 page Class Notes was uploaded by Madeline Wilson on Thursday February 25, 2016. The Class Notes belongs to GEOL 101 001 at University of South Carolina taught by Dr. Knapp in Spring 2016. Since its upload, it has received 18 views. For similar materials see Introduction to the Earth in Geology at University of South Carolina.
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Date Created: 02/25/16
Early History of Terrestrial Planets Eons are the largest division of geologic time Nuclear Fusion is the process in which hydrogen atoms combine to form helium under intense pressure and high temperature Nuclear Fusion vs. Fission Nuclear fission is the splitting of an atom into two or more smaller ones Nuclear fusion is the fusing of two or more smaller atoms into a larger one Fusion occurs in stars, such as the sun, whereas fission reaction does not normally occur in nature Origin of Solar System The universe is thought to have begun about 14 billion years ago – “Big Bang Theory”, primeval cosmic explosion Since then, the universe has expanded to form the galaxies, stars, and planets The best existing explanation for the known observations and physical laws The Nebular Hypothesis A diffuse, roughly spherical, slowly rotating nebula begins to contract Formation of the Sun – Solar Nebula Due to gravity, the mass started to drift toward the center, creating the proto-sun Compressed under its own weight, the material in the proto-sun became dense and hot The internal temperature of the proto-sun rose to millions of degrees, at which point nuclear fusion began This nuclear fusion continues today, and it is similar with the nuclear reaction that occurs in the nuclear bomb Planetesimals Once formed, the disk started to cool, and many of the gasses condensed Planetesimals – any of numerous small solid celestial bodies that may have existed at an early stage of the development of the solar system Planetesimals grew by colliding with each other to planets such as the earth The Nebular Hypothesis (at the basis of Solar System formation) A large gas and dust cloud (nebula) begins to condense Gas mostly (H, He) Most of the mass is in the center Contraction of cloud due to gravity Small chunks grow and collide forming larger aggregates The Solar System Planets Inner planets began to accrete about 4.56 bya They grew to the planetary size in less than 100 million years The inner planets are mostly formed of rocks and metals The outer larger planets (giant planets) are made up primarily of ice and gasses, although they have an iron core No two planets are the same The definition of “planet” In the solar system a planet is a celestial body that 1. Is in orbit around the sun 2. Has sufficient mass so that is assumes hydrostatic equilibrium (nearly round) shape 3. Has “cleared the neighborhood” around its orbit If only two of the condition above are met, the status is of a “dwarf planet” Formation of the moon (about 4.5 billion years ago) ~4.5 bya, a mars-sized body impacted the earth, and the giant impact quickly propelled a shower of debris from both the impacter and the earth into space The impact sped up the earth’s rotation and tilted the earth’s orbital plane 23 degrees Earth reformed as a largely molten body, and the moon aggregated from the debris Moon rocks ~4.47 bya The Early Earth Heats Up Accretion of meter-sized bodies Collisions: transfer of kinetic energy into heat Compression under gravitational attraction Radioactive elements (e.g. uranium, potassium, or thorium) continue to keep the interior of the earth hot Chemical Differentiation Continents: solidified magma that floated up from the mantle Oceans and atmosphere: fluid outer later derived from volatile transfer gases from the interior (and perhaps from comets) Even today, trapped remnants of the original solar nebula continue to be emitted as primitive gases in volcanic eruptions Volatile transfer Photosynthesis by microorganisms removed carbon dioxide and added oxygen to the primitive atmosphere Inner planets Mercury – very hot/cold, many craters, thin He atmosphere Venus – very hot, covered by lava flows, thick acid atmosphere Earth – usually pretty nice, lots of water, nitrogen-oxygen atmosphere Mars – cold, many craters and dry river valleys, thin carbon-dioxide atmosphere Moon Earth’s moon – cold, many craters (shows evidence of period of heavy bombardment by asteroids), no atmosphere Outer planets Gaseous bodies made mainly of hydrogen and helium 1. Jupiter 2. Saturn 3. Uranus 4. Neptune Age and complextion of planetary surfaces Earth 1. Core-mantle separation (4400 mya) 2. Liquid oceans form (4000 mya) 3. End of heavy bombardment (3900 mya) Impact craters on earth? 1. Found on continents 2. Rare structures formed by meteorite or asteroid impacts Moon 1. Formation of highlands (4400 to 4000 mya) 2. Formation of lunar maria (4000 to 3200 mya) Mercury 1. Impacts and lava flows 2. Cooling and contraction Venus 1. Flake tectonics 2. Extensive lava flows (oldest surface 500 mya) Mars 1. Formation of ancient cratered terrains (3900 to 3800 mya) 2. Period of water flows (3900 to 3500 mya) Mercury Fault scarp produced by cooling and contraction of mercury Mariner 10 (1974) the first spacecraft to visit mercury and flew by it “Messenger” mission to mercury (2011) New evidence for flood volcanism First close-up views of mercury’s “hollows” First direct measurements of the chemical composition of mercury’s surface The first global inventory of plasma ions within mercury’s space environment
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