Geologic Time and Origins of the Earth

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Geologic Time and Origins of the Earth
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Thinking about time

• Geologic time vs. normal time
• What is the date today?
• What is the day?
• What is the time?
• Why do we care?

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Geologic time

• Thinking in terms of millions of years
• Try it in seconds, just for fun
• 1,000,000 seconds
• How many minutes is this?
• 1,000,000 seconds / 60 seconds per minute
• This 16,667 minutes
• How many hours is this?
• 16,667 / 60 minutes per hour 278 hours
• How many days?
• 278 hours / 24 hours per day 11.6 days
• So, 1 million seconds 12 days

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How does 1 million compare to 1 billion?

• Again, in seconds just for fun
• 1,000,000,000 seconds
• How many minutes is this?
• 1,000,000,000 seconds / 60 seconds per minute
• This 16,666,667 minutes
• How many hours is this?
• 16,666,667 / 60 minutes per hour 277,778 hours
• How many days?
• 277,778 hours / 24 hours per day 11,574 days

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Keep going

• 11,574 days--how many weeks is this?
• 11,574 / 7 days per week 1,653 weeks
• Great, now how many years is this?
• 1,653 weeks / 52 weeks per year
• This equals 32 years
• So, one billion seconds 32 years
• And one million seconds 11 days
• Now instead of seconds, lets think in YEARS

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Geologic time

• Video clip Carl Sagan and the Cosmic Calendar
  (5-7 minutes)
• From the Cosmos Public Television Series, 1981
• Episode 1, The Shores of the Cosmic Ocean
• About 10 minutes before the end
• Available at the UTEP Library for viewing

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Geologic Time

• The big divisions are
• Proterozoic time before 544 m.y.a.
• Paleozoic time from 544 - 245 m.y.a.
• Mesozoic time between 245 - 66 m.y.a.
• Cenozoic time between 66 - 2.5 m.y.a.
• Even MORE divisions

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Geologic time scale
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Earth Origins

• AFTER Big Bang
• Earth Origins are described by the Nebular
  Hypothesis
• RECAP Scientific Terms
• Hypothesis provisional explanation for
  observations subject to continued testing
  modification
• Theory An explanation for some natural
  phenomenon that has a large body of supporting
  evidence testable repeatable

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Nebular Hypothesis 1

• Solar system did not exist 5 billion years ago
• A giant cloud of dust and gas occupied this area
  of space
• Many times larger than the present solar system
• A lot of space between individual atoms of gas,
  metal and ions
• Why do we think this?
• We observe large gas clouds in space, which
  contain basic building blocks of our solar system

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Nebular Hypothesis 2

• Something caused this cloud to condense
• Maybe a nearby star exploded, sending its mass
  out into space
• This mass collided with our dust cloud
• Forcing atoms and dust grains to collide
  (accretion)
• Each atom grain has its own gravity
• The bigger the grain, the bigger its gravity
• The bigger the gravity, the bigger the chance for
  accretion
• (snowballing effect like positive feedback)

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N.H. 2, continued

• Nearby supernova caused cloud to condense
• Accretion began
• Why do we think this?
• We have seen supernovae
• We have seen the remainder of star mass ejected
  into space
• We can mathematically model what happens when
  this mass collides with gas clouds

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Nebular Hypothesis 3

• Cloud continues to condense
• Center of cloud attracts the most matter
• Cloud flattens into a disk and begins to rotate
• Incredible amount of heat generated in the center
• So much heat that atoms are fused together, and
  the sun turns on
• Why do we think this?
• Explains the similar rotation of all planets
• Explains how the planets are all orbiting in one
  plane (DISK)
• Explains location of sun
• Explains motion that we see in other gas clouds

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Nebular Hypothesis 4

• A new sun in the center of a disk of dust
• More volatile elements move away from the sun
• H, He, Methane, Ammonia
• Accretion continues in the disk
• Planets form by collision
• Why do we think this?
• Explains why inner planets are rocky outer
  planets are gaseous
• Explains old craters on planetary surfaces

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Nebular Hypothesis 5

• Accretion continued until most of the matter
  accreted into planets
• Accretion occurred in stages, with the Late
  Heavy Bombardment happening 3 b.y.a.
• Why do we think this?
• Explains relative emptiness between planets
• Explains different apparent ages of craters on
  moon, Mars
• Explains old craters on planetary surfaces

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Nebular Hypothesis

• Video Clip Carl Sagans Cosmos Series
• Episode 8, Travels in Space Time
• Available for viewing at the UTEP library
• About 15 minutes before the end of the episode

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Why is the N.H. a hypothesis and not a theory?

• Observations are indirect
• We were not there to see it
• What we can see is very slow
• So
• we do not try to produce a solar nebula model
  that exactly describes our Solar System and the
  planetary orbits and their masses
• rather we look for a model that describes the
  characteristic properties of the planets at their
  observed locations in the Solar System

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Making the Earth 1

• Accretion acts over an extended area (the disk)
  and for a extended period of time
• Solid grains condense out of the nebulas gas
• This is a chemistry process
• Grains accrete into larger bodies (planetesimals)
• This is a dynamic, collisional process
• Planetesimals collide to produce protoplanets
• Protoplanets accrete more material and become
  genuine planets

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Making the Earth 2

• Earth cools a bit
• Elements, minerals condense/crystallize
• Iron, nickel, then rocky material
• Layered Earth forms
• Stays molten due to heat of radioactive elements
  and L.H.B.
• Iron and nickel sink to center, rocky material
  floats outward (density sort).
• This is called differentiation

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Layered Earth