Origin of solar system

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Origin of solar system

• Big Bang theory
• Broadly accepted theory for the origin and
  evolution of our universe
• Postulates that the observable universe started
  from an instantaneously expanding point 13 to 14
  billion years ago
• Since then, the universe has continued to expand
• Prior to Big Bang, all matter and energy were
  compacted into single, inconceivably small dense
  point

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Evidence for Expanding Universe

• Astronomers looking at distant galaxies directly
  observe this expansion
• Originally detected by Edwin Hubble
• The expansion of the universe "stretches" light
  rays converting blue light into red light and red
  light into infrared light
• Example of a Doppler effect
• Thus, distant galaxies, which are rapidly moving
  away from us appear redder
• Geologists look to the formation of the solar
  system to understand formation of the Earth

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Evidence for Big Bang

• Expansion of the Universe
• Abundance of helium, deuterium and lithium
• Thought to be synthesized primarily in the first
  three minutes of the universe
• Thermal spectrum of cosmic microwave background
  radiation
• The universe is filled with the remnant heat from
  the Big Bang called the "cosmic microwave
  background radiation
• Today, this radiation is very cold only 2.728
  degrees above absolute zero. It fills the
  universe and can be seen almost everywhere we
  look
• Cosmic microwave background radiation appears
  hotter in distant clouds of gas
• Since light travels at a finite speed, we see
  these distant clouds at an early time in the
  history of the universe, when it was denser and
  thus hotter

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What Big Bang does not Explain

• Origin of galaxies and the observed large-scale
  clustering of galaxies
• Astronomers observe considerable structure in the
  universe, from stars to galaxies to clusters and
  superclusters of galaxies
• "Deep Field Image" taken by the Hubble Space
  Telescope, provides a view of such structure
• How did these structures form?
• Most astrophysicists believe that the galaxies
  that we observe today grew gravitationally out of
  small fluctuations in the nearly-uniform density
  of the early universe
• These fluctuations leave an imprint in the cosmic
  microwave background radiation in the form of
  temperature fluctuations from point to point
  across the sky
• Origin of the uniform distribution of matter on
  very large scales

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Origin of solar system

• Pick a theory, any theory, but it must be
  consistent with these facts
• Planets all revolve around the Sun in the same
  direction in nearly circular orbits
• Counterclockwise direction
• The angle between the axis of rotation and the
  plane of orbit is small (except Uranus)
• Roughly perpendicular to the plane of orbit

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Origin of solar system

• Pick a theory, any theory, but it must be
  consistent with these facts
• All planets (except Venus and Uranus) rotate in
  the same direction as their revolution their
  moons do, too
• Counterclockwise direction
• Each planet is roughly twice as far as the next
  inner planet is from the Sun

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Origin of solar system

• 99.9 of mass is in the Sun 99 of angular
  momentum is in the planets
• Sun rotates very slowly
• Planets in two groups with different chemical and
  physical properties
• terrestrial (inner) Mercury, Venus, Earth, Mars
  Mercury is mostly Fe (? 5.4)
  
• Jovian (outer) Jupiter, Saturn, Uranus,
  Neptune. Jupiter mostly gas and ice ( ? 0.7)
  Pluto ????

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Origin of solar system

• Terrestrial planets are mostly O, Si, Fe, Mg.
  The Sun is almost entirely H He (also important
  in Jovian planets)
• Interplanetary material
• Existence of asteroid belt between terrestrial
  and Jovian planets
• Existence of planetary dust

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Nebular hypothesis

• Primeval nebula (slowly rotating cloud of He and
  H gases dust)
• Initially cloud are stable and move slowly
• Occasionally they are disrupted by shock waves
  from exploding star called a Supernova

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Nebular hypothesis

• Massive explosions create turbulence in the dust
  cloud induce gravitational instabilities
• Gas cloud contracts under the force of gravity
  and flattens
• As a result the cloud starts to rotate in order
  to conserve its original angular momentum

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Nebular hypothesis

• Eventually, the increasing speed of rotation
  causes the cloud to collapse into a flat disk

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Nebular hypothesis

• Sun forms and dust particles collide and clump
  together to form planetesimals

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Nebularhypothesis
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Our Solar System
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Evidence for the Nebular Hypothesis

• Because of the original angular momentum and
  subsequent evolution of the collapsing nebula,
  this hypothesis provides a natural explanation
  for some basic facts about the Solar System
• The orbits of the planets lie nearly in a plane
  with the sun at the center (neglecting the slight
  eccentricity of the planetary orbit)
• The planets all revolve in the same direction
• The planets mostly rotate in the same direction
  with rotation axes nearly perpendicular to the
  orbital plane
• The nebular hypothesis explains many of the basic
  features of the Solar System, but we still do not
  understand fully how all the details are
  accounted for by this hypothesis

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Collision hypothesis

• Portions of the Sun were torn off by a passing
  star planetesimals then collided to form
  planets.
• Problems gases coming from Sun would be too hot
  to condensestellar collision exceedingly rare.

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Protoplanet hypothesis

• Large gas cloud begins to condense.
• Most mass in center, turbulence in outer parts.
• Turbulent eddies collect matter meter across
  small chunks grow and collide, eventually
  becoming large aggregates of gas and solid
  chunks.
• Protoplanets, much bigger than present planets,
  eventually contracted due to their own gravity.

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The Moon

• Only a little smaller than Mercury (small planet
  in two-planet system).
• Surface of the moon very different from the
  surface of Earth.
• No atmosphere, therefore, no weathering.

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Formation of the Moon

• Mars-sized body collides with Earth 4.5 Billion
  yr BP
• Debris ejected to form Moon

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A catastrophic impact between theproto-Earth and
a Mars-sized impactor
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Timeline for the Sun, Earth, and Moon
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Why worry about the beginning?

• The evolutionary course is significantly
  influenced by the initial state.
• We know the state of the Earth today relatively
  well knowing the beginning will help constrain
  the in between.

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A Differentiating Planet
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Heating of Planet

• Accretion. Impacting bodies bombard the Earth and
  convert their energy of motion into heat
• Gravity. As the Earth gets bigger, the extra
  gravity forces the mass to contract into a
  smaller volume, producing heat
• Just like a bicycle pump gets hot on compression
• Radioactive Disintegration. The surrounding
  material absorbs the energy released in
  radioactivity, heating up
• This is a very slow but steady source of heat
• About 20 calories of heat are generated by 1
  cubic centimeter of granite in the course of a
  million years
• It would take this amount of rock 500 million
  years to brew a cup of coffee!

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An Early Homogeneous Earth
Early Earth was a homogenous body
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Differentiation

• Rock is a very poor conductor of heat
• So heat continued to build up until some
  materials started to melt
• Calculations have been carried out to determine
  what happened to the early "homogenous" earth
  before differentiation
• At some point, probably during the first few
  hundred million years of Earth history a region
  at a depth of 500 km became so hot that iron (a
  plentiful element) started to melt
• The molten iron collected and began to sink under
  its own weight.
• About one third of the primitive planet's
  material sank to the center and in the upheaval
  heating rates increased and a large part of the
  body was liquefied

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Differentiation Begins
Irons sinks to the interior and lighter
material floats upward
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Differentiation

• The formation of a molten iron core was the first
  stage of the differentiation
• Converted Earth from a homogenous body with
  roughly the same kind of material at all depths
  to a zoned, or layered body with a dense iron
  core, a crust composed of lighter materials with
  lower melting points and between them the mantle
• The first stage of differentiation iron melting
  (which took a long time to occur) led to the
  onset of a mechanism that speeded up the
  differentiation
• Convective overturn -- a process whereby molten
  material may overturn, transferring heat buried
  deeply within the planet to the outer layers

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Present day Earth
Now Earth is a zoned planet with a dense core
and lighter crust
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Differentiation

• Perhaps the most significant event in the history
  of the Earth
• It led to the formation of a crust and eventually
  the continents
• Differentiation probably initiated the escape of
  gases from the interior
• eventually led to the formation of the atmosphere
  and oceans

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Origins of the Atmosphere

• Some geologists believer that most of the air and
  water on Earth came from volatile-rich matter of
  the outer solar system that impacted Earth as it
  formed
• Countless comets may have bombarded Earth
  bringing water and gas that gave us our oceans
  and atmosphere
• The very hot young Earth would also have lots of
  volcanic activity leading to outgassing of
  volatile gases from within the magma
• Originally water and gases were locked up in
  minerals
• There is evidence that the hot outgassing that
  occurred during the first billion years also led
  to the first atmosphere of the Earth

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Interacting Earth SystemsVolcanoes contribute
gases to the atmosphere and solids to the crust
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Atmospheric Gases

• Did not inherit all our atmosphere from ancestral
  bodies
• Water vapor and other gasses released from rocks
  by outgassing
• Outgassing by volcanic emission occurs today
• Water vapor, H, HCl, CO, CO2, N2
• Early atmosphere higher H content
• Possibly also ammonia and methane
• Gasses from modern volcanoes from recycled rocks
• Reasonably sure early atmosphere not from
  accretion
• i.e., accumulation of light volatiles from nebula
• Relative scarcity of inert gasses in modern
  atmosphere
• Ar, Ne, Krypton
• Too heavy to escape from earths gravity
• Less abundant than in atmosphere of stars
• Our atmosphere not residue of gasses from nebula

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Rapid Degassing

• Rapid degassing must have produced much water
  vapor
• Condense to form seas when earth cooled
  sufficiently
• Know oceans formed early
• Water laid sediments
• Metamorphosed sediments date 3.8 by
• Detrital grains 4.4 by

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Big Burp

• If the Big Bang led to all the universe
• The "Big Burp" of differentiation led to much of
  the environment we live in
• It could have occurred over millions of years or
  it could have been a more catastrophic event
• The earliest Earth was probably an unsorted
  conglomeration
• Mostly silicon compounds, iron and magnesium
  oxides and smaller amounts of all the natural
  elements

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Relative Abundance of Elements
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Earth System Science

• Earth should be studied as a unified system
• Interactions and interrelationships between all
  Earth systems
• Earth can be divided into 4 subsystems
• Biosphere
• Lithosphere
• Hydrosphere
• Atmosphere
• Materials and energy cycle among these these
  subsystems

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Lithosphere, Hydrosphere, Atmosphere, Biosphere
and Uniformitarianism
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Interacting Earth Systems
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Kinds of Systems
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Example of an Open System
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Another view of the hydrologic cycle
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The Earth is a Closed System
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CO2 and Long-Term Climate

• What has moderated Earth surface temperature over
  the last 4.55 by so that
• All surface vegetation did not spontaneously
  catch on fire and all lakes and oceans vaporize?
• All lakes and ocean did not freeze solid?

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Greenhouse Worlds

• Why is Venus so much hotter than Earth?
• Although solar radiation 2x Earth, most is
  reflected but 96 of back radiation absorbed

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Energy Budget

• Earths temperature constant 15?C
• Energy loss must incoming energy
• Earth is constantly receiving heat from Sun,
  therefore must lose equal amount of heat back to
  space
• Heat loss called back radiation
• Wavelengths in the infrared (long-wave radiation)
• Earth is a radiator of heat
• If T gt 1?K, radiator of heat

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Energy Budget

• Average Earths surface temperature 15?C
• Reasonable assumption
• Surface of Earth radiates heat with an average
  temperature of 15?C
• However, satellite data indicate Earth radiating
  heat average temperature -16?C
• Why the discrepancy?
• What accounts for the 31?C heating?

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Energy Budget

• Greenhouse gases absorb 95 of the long-wave,
  back radiation emitted from Earths surface
• Trapped radiation reradiated down to Earths
  surface
• Accounts for the 31?C heating
• Satellites dont detect radiation
• Muffling effect from greenhouse gases
• Heat radiated back to space from elevation of
  about 5 km (top of clouds) average 240 W m-2
• Keeps Earths temperature in balance

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Energy Balance
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Greenhouse Worlds

• Why is Venus so much hotter than Earth?
• Although solar radiation 2x Earth, most is
  reflected but 96 of back radiation absorbed

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What originally controlled C?

• In solar nebula most carbon was CH4
• Lost from Earth and Venus
• Earth captured 1 in 3000 carbon atoms
• Tiny carbon fraction in the atmosphere as CO2
• 60 out of every million C atoms
• Bulk of carbon in sediments on Earth
• CaCO3 (limestone and dolostone) and organic
  residues (kerogen)
• Venus probably had similar early planetary
  history
• Most carbon is in atmosphere as CO2
• Venus has conditions that would prevail on Earth
• All CO2 locked up in sediments were released to
  the atmosphere

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Earth and Venus

• Water balance different on Earth and Venus
• If Venus and Earth started with same components
• Venus should have either
• Sizable oceans
• Atmosphere dominated by steam
• H present initially as H2O escaped to space
• H2O transported "top" of the Venusian atmosphere
• Disassociated forming H and O atoms
• H escaped the atmosphere
• Oxygen stirred back to surface
• Reacted with iron forming iron oxide

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Planetary Evolution Similar

• Although Earth and Venus started with same
  components
• Earth evolved such that carbon safely buried in
  early sediments
• Avoiding runaway greenhouse effect
• Venus built up CO2 in the atmosphere
• Build-up led to high temperature
• High enough to kill all life
• If life ever did get a foothold
• Once hot, could not cool

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Why Runaway Greenhouse?

• Don't know for sure why Venus climate went
  haywire
• Extra sunlight Venus receives?
• Planet too hot for liquid water
• Life perhaps never got started?
• No sink for carbon in organic matter
• Was the initial component of water smaller than
  that on Earth?
• Did God make Venus as a warning sign?