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
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
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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
Chondrites
Chondrite
The Earth’s Crust looks Very Different
Composition of the Crust
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
Three Images of Early Earth
Chesley Bonestell’s Classic Image
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
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Apollo samples: Moon had “magma ocean”
Better understanding of impact physics
Role of mega-impacts
Formation of core
Magma Ocean by Ron Hartmann
Craters and Planetary History
• Superposition
• Crater Saturation
• Crater Degradation
Superposition
Crater Saturation
Crater Degradation
Biggest and Oldest Crater on the Moon
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
Basalt
and
Anorthosite
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
Mega-Impacts:
As Usual, Gary
Larson Gets
There First
Computer Simulations by H.J.
Melosh (University of Arizona)
Formation
of the
Moon
Formation of the Moon
View from the
early Moon
Earth 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
Bonestell: The Earth Cools
Bonestell: The Oceans Form
Hartmann: The First Moonrise
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?
Molasse,
Switzerland
Molasse and the High Alps
Archean Granite
Archean Pillow Lava
Archean Iron Formation
3.1 Billion Year Old Gneiss
Archean North America
Bear and Nain Provinces
Rae Block Collides
Penokean About
to Begin
Penokean Orogeny and
Churchill Collision
Wyoming Province
Collision
Hearne Block Collides
Trans-Hudson Orogeny
Mazatzal
Orogeny
Yavapai
Orogeny
Midcontinent
Rift Forms
Grenville
Orogeny
Complete
Present
North
America