Earth

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Earths Early History

• How did it all get started?

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Quiz--Reading Ch. 12, and Birth of Earth Video
1. What gas made up most of the earths early
atmosphere? 2. What significant biological event
took place at the end of both the Ordovician and
Permian Periods? 3. What is a half-life? Define
and tell what application this has in biology. 4.
Which of the following statements do you think is
most true? Choose the one that you think is most
correct and explain/defend your
answer. Changing/Evolving biological organisms
have caused major geological changes. Geological
changes have caused/stimulated major biological
changes (evolution).
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Formation of Earth

• Major events
• Solar system formed from swirling gases and dust
  (6 bya)
• Rocks in solar system condensed to form Earth
  (4.5 bya)
• Center of Earth melted by great pressure and
  intense heat
• Surface of earth cooled, forming crust (4.1 bya)
• Atmosphere formed as Earth cooled

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The Dilemma of early life

• Redi and spontaneous generation
• How did the 1st life originate?
• Scientists have reconstructed what the early
  atmosphere and environment was like
• Heavier elements (nickel and iron) settled to the
  center of earth and formed the core
• Lighter elements (hydrogen, helium, other gases)
  cooled to form crust and atmosphere
• Frequent violent volcanic eruptions spewed other
  gases into the atmosphere

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The Early Atmosphere

• The gases from eruptions inferred by studying
• Current volcanic eruptions on earth
• Atmosphere of other planets
• Gases present
• Carbon dioxide (CO2)--92
• Nitrogen (N2)
• Sulfur dioxide (SO2)
• Water vapor that condensed and came down in
  storms
• but little or no Oxygen (O2)!
• What gases are in our current atmosphere?

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Input of Energy

• Without ozone, the Earth was affected differently
  by the sun
• Intense lightning storms may have also provided
  great energy

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Possible steps in life formation
1. Inorganic Matter
2. Simple Organic molec.
3. Polymers
4. Protocells
5. Cells!
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An overview of the steps

• Organic molecules (chemical evolution)
• Alexander Oparin (Russian scientist) hypothesized
  that energy from lightning/UV could convert
  inorganic molecules to organic
• Miller and Urey tested this idea in 1953
• Apparatus combined water vapor, methane, ammonia,
  and hydrogen
• Heat and electrical energy added
• Organic molecules produced
• A variety of mixtures have produced a variety of
  chemicals (ATP, nitrogenous bases, amino acids)
• But did this really mimic the conditions of the
  early earth!???
• Francis Crick hypothesized that complex chemicals
  came to earth in a meteorite

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Miller and Ureys Apparatus
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The Heterotroph Hypothesis

• The first organisms on the Earth were
• Anaerobic--there was no oxygen
• Heterotrophs--obtained energy from other material
  (no photosynthesis at first..or there would have
  been oxygen!)
• Prokaryotes--simple bacterial cells
• Then followed..photosynthetic prokaryotes,
  aerobic prokaryotes, eukaryotes, multicellular
  organisms

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The Geological Clock

• Humans have been on Earth for about 250,000
  years--is only seconds on the geological time
  clock
• Time periods broken into eras, periods, etc.
• Periods are marked by the extinction of some
  species and the appearance of others
• Age of fossils dated with radioactive isotopes
• The Cambrian explosion--beginning of Cambrian
  period showed explosion of spp.

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Radioactive Elements and dating

• Radioactive isotopes--versions of elements that
  spontaneously break down (decay)
• Occurs at constant/predictable rate
• 3 Types of radiation particles
• Alpha--structure of helium nucleus
• Beta--high speed electrons
• Gamma--like X-rays
• When alpha particle is released, different
  element results, which may also be radioactive

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Half-Life

• Half-life--time it takes for 1/2 of the atoms in
  a sample to change/decay
• Since decay takes place at constant rate, can use
  to determine dates on old objects
• Ratio of radioactive material to stable end
  product can be compared to determine age
• Half-life varies from fraction of second to
  billions of years (U-238 4.5 billion yrs)

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Radiocarbon dating

• Radiocarbon dating uses carbon-14
• Half-life is 5700 years
• Compares ratio of normal carbon (carbon-12) to
  amount of carbon-14
• Can be used on things that were once living
• Used for relatively young dates

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Other radiometric methods

• Uranium-lead
• U-238 decays to Pb-206 in 4.5 billion years
• Used for some very old igneous rock dates
• Rubidium-strontium
• Rubidium-87 decays to Sr-87 in 49 billion years!
• Rubidium-87 occurs in nearly all igneous rocks
• Can sometimes be used to verify U-238 dates
• Potassium-argon
• K-40 decays to Ar-40 in 1.3 billion years
• Advantageous since K is a very common element in
  potash feldspar and black mica
• Found in all rock types
• Can date rocks as young as 50,000 years

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And then the land changed

• Plate tectonics--movement of the earths crustal
  plates
• Global warming and cooling, often triggered by
  volcanic eruptions (again driven by plate
  tectonics)

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Mass Extinctions

• Huge extinctions came at the end of the
  Cretaceous and Permian periods
• Possible causes
• Changing climate driven by volcanic eruptions
  (ash in sky hides sunlight)
• Impact of comet or meteorite