Formation of The Earth
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Transcript of Formation of The Earth
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Formation of The Earth
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Composition of the Sun
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The Most Unusual ElementAdministratium (Ad)• No protons: Atomic Number Zero• One neutron• 27 Assistant neutrons• 137 Deputy assistant neutrons• 332 Associate neutrons• Detectable indirectly: slows down all
reactions it participates in
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Composition of the Sun
• Abundance of Light Elements
• Rarity of Lithium, Beryllium, Boron
• Preference for Even Numbers
• Abundance peak at Iron, trailing off after
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How Elements Form in Stars
• Sun: 4 H He• He + particle Mass 5 – Unstable• He + He Mass 8 – Unstable• He + He + He C• Add more He to make heavier elements• End of the line is iron for energy production• Atoms beyond Iron made in massive stars
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What are Planets Made of?
• Same material as Sun• Minus the elements that remain mostly in
gases• We find this pattern in a certain class of
meteorites
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Chondrites
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Chondrite
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The Earth’s Crust looks Very Different
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Composition of the Crust
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Hot or Cold?
• Up to 1940: Earth is hot inside, so must have formed hot
• 1940-1970: Earth need not have formed hot• 1970- Earth did form hot after all
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Hot Early Earth?
• Lord Kelvin, 1862: estimate age of Earth from cooling.– Earth’s heat is left over from its formation– Heat travels outward by conduction– Earth is not producing heat
• Only one problem (actually three): Every one of Kelvin’s assumptions was wrong
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Three Images of Early Earth
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Chesley Bonestell’s Classic Image
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Nuclear Processes
• Radioactivity (Becquerel, 1896)• Importance for Earth history:– Used for dating rocks– Explains sun’s energy output– Earth does produce heat
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Maybe Earth Formed Cool?
• Planets formed by accretion of smaller bodies• Each impact produces heat• If rate is slow enough, heat can radiate away
as fast as it is produced
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Earth Formed Hot After All
• Apollo samples: Moon had “magma ocean”• Better understanding of impact physics• Role of mega-impacts• Formation of core
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Magma Ocean by Ron Hartmann
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Craters and Planetary History
• Superposition• Crater Saturation• Crater Degradation
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Superposition
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Crater Saturation
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Crater Degradation
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Biggest and Oldest Crater on the Moon
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Impact History
• Earliest records on Moon, Mars and Mercury: Intense Cratering
• As planets grow, their gravity increases. Impacts get more violent
• Debris from impacts buries hot rocks from earlier impacts
• Heat builds up• Magma Ocean
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Basalt and
Anorthosite
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How Do Planets Accrete?
• Tiny objects can be held together by welding, electrical forces, chemical interactions
• Big objects hang on to incoming material by gravity
• Things the size of a car are the mystery right now
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Computer Studies
• Start with as many orbiting objects as your computer can handle
• Let them collide• Don’t get 8-10 nice, regular planets• Get 100’s of Moon and Mars-sized objects• These collide to make bigger planets• Violent beyond your wildest dreams
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How Did the Moon Form?
• Co-Creation?• Fission?• Capture?
• 1985: Bill Kaufmann, Jay Melosh and others: Mega-Impact
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Mega-Impacts:
As Usual, Gary Larson Gets There First
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Computer Simulations by H.J. Melosh (University of Arizona)
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Formation of the Moon
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Formation of the Moon
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View from the early Moon
Earth would have been as
hot as the Sun for 10,000
Years
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Earth’s Atmospheres and Oceans• Primordial from accretion• Magma Ocean• Mega-Impacts (1000 km +)– Magma Ocean– Vaporized Rock (100’s years)– Steam
• Smaller Impacts (100 km +)– Vaporized Rock (Years)– Steam (Boil off Oceans)
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Earth Finally Settles Down
• Origin of Atmosphere and Oceans?– Outgassing?– Impacts of comets?
• Early Atmosphere Probably Mostly CO2, and H2O
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Bonestell: The Earth Cools
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Bonestell: The Oceans Form
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Hartmann: The First Moonrise
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The Very Early Earth (Hadean)• Intense cratering on Moon (and
presumably Earth) ends about 4 billion years ago.
• Oldest earth material: 4 billion year old zircon from Australia.
• Oldest rocks: 3.9 billion years, NW Canada.• Minnesota River Valley rocks: 3.1 billion
years.• Can’t say much about processes• Liquid water from the git-go
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The Faint Early Sun
• Sun 4 billion years ago was only 70% as bright as now.
• Would make average temperature of earth -15 F (-26 C)
• But earth has always had liquid water• Must have had denser atmosphere, greater
greenhouse effect.
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The Archean• 3.0 – 2.5 billion years ago• About half of earth’s continental crust
forms• Granite, deep-water sediments and
volcanic rocks, deep crustal rocks• Were there mountains?• Did Plate Tectonics exist?
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Molasse, Switzerland
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Molasse and the High Alps
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Archean Granite
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Archean Pillow Lava
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Archean Iron Formation
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3.1 Billion Year Old Gneiss
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Archean North America
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Bear and Nain Provinces
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Rae Block Collides
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Penokean About to Begin
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Penokean Orogeny and Churchill Collision
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Wyoming Province Collision
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Hearne Block Collides
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Trans-Hudson Orogeny
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Mazatzal Orogeny
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Yavapai Orogeny
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Midcontinent Rift Forms
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Grenville Orogeny Complete
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Present North America