Transcript time and origins power point

Geologic Time and
Origins of the Earth
Thinking about time
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Geologic time vs. “normal” time
What is the date today?
What is the day?
What is the time?
Why do we care?
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
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
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?
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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
Geologic time
• Video clip: Carl Sagan and the Cosmic
Calendar (5-7 minutes)
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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
Geologic Time
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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
Geologic time scale
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
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
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)
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
Nebular Hypothesis 3
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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
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
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
Nebular Hypothesis
• Video Clip: Carl Sagan’s Cosmos Series
– Episode 8, “Travels in Space & Time”
– Available for viewing at the UTEP library
– About 15 minutes before the end of the episode
Why is the N.H. a hypothesis
and not a theory?
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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
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 nebula’s 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
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
Layered
Earth