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Formation of The Earth. Composition of the Sun. The Most Unusual Element. Administratium (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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The Most Unusual Element Administratium (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
Composition of the Sun • Abundance of Light Elements • Rarity of Lithium, Beryllium, Boron • Preference for Even Numbers • Abundance peak at Iron, trailing off after
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
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
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
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
Nuclear Processes • Radioactivity (Becquerel, 1896) • Importance for Earth history: • Used for dating rocks • Explains sun’s energy output • Earth does produce heat
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
Earth Formed Hot After All • Apollo samples: Moon had “magma ocean” • Better understanding of impact physics • Role of mega-impacts • Formation of core
Craters and Planetary History • Superposition • Crater Saturation • Crater Degradation
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
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
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
How Did the Moon Form? • Co-Creation? • Fission? • Capture? • 1985: Bill Kaufmann, Jay Melosh and others: Mega-Impact
View from the early MoonEarth would have been as hot as the Sun for 10,000 Years
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)
Earth Finally Settles Down • Origin of Atmosphere and Oceans? • Outgassing? • Impacts of comets? • Early Atmosphere Probably Mostly CO2, and H2O
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
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.
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?