The evolution of life

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The evolution of life
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Evolution of life

• Creation of amino acids
• Creation of the first self replicating molecule
  the random replicator
• Enclosure of self replicating molecules within a
  vesicle or pre-cell

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Evolution of life
4. pre-cells develop self-catalyzing RNA
strands 5. Development of genetic code to
transcribe RNA into DNA 6. Natural selection
favors cells with DNA which can be quickly and
accurately copied
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Earliest cells

• Prokaryotes
• Anaerobes
• Chemoautotrophs

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Discussion
Why must the earliest life forms be prokaryotes?
Why not eukaryotes?
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Discussion
Why must they have been anaerobic? Why not
aerobic?
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Discussion
Why must they have been autotrophic, getting
their carbon from CO2?
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Discussion
Why do we think they were chemoautotrophes and
not photoautotrophes?
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Development of photosynthesis
Prokaryotes evolved pigments to shield themselves
from UV light Extra heat and energy from the
absorbed light could be used
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Discussion
All of the above steps had to be made in less
than 250 million years. If the creation of life
from non-life is as easy as astrobiologists
claim, why do we have only one kind of life on
Earth?
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Amebas
ameba video
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Eukaryotes and endosymbiosis
Mitochondria aerobic production of
ATP Chloroplasts photosynthesis
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Build-up of oxygen
Banded iron formations Sulfur isotopes
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The Burgess Shale
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Cambrian explosion

• Rise of oxygen
• Evolution of genetic complexity
• End of the last snowball earth
• Lack of predators

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Discussion
What is an ice age? How would you explain it to
someone else?
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Ice ages
Snowball Earth episodes are not the same as ice
ages
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Earths rotation
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Discussion
Why is Kennedy Space Center in Florida and not in
Maine?
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Centrifugal force
This extra velocity at the equator pushes the
matter out at the equator.
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The Earth is not a perfect sphere
The Earth bulges out at its equator. Its
diameter measured along its equator is 43 km
larger than its diameter from the north to the
south pole.
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The Earths rotation axis remains in a fixed
direction as Earth orbits the Sun.
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Sun and Moon apply a torque
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Precession
This off axis force, or torque, on the Earth
causes Earths rotation axis to vary slightly, or
precess, over long periods of time. Thus, the
celestial poles trace out a circle against the
stars over a period 26,000 years.
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Sidereal year vs. tropical year
Our calendar year is shorter than the actual
orbital period of the Earth by just over 20
minutes. Time of year that Earth is furthest
from Sun changes over the years.
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Discussion
Are the winters as bad as they can get for us
northerners? What about the southern hemisphere?

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Earth tilt is not constant
Due to torques supplied by the other planets,
Earths tilt changes form 22.5 degrees to 24.5
degrees with a period of 41,000 years.
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Discussion
Are glaciers more likely when the seasons are
extreme or when there is little variation between
seasons?
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Earth orbital eccentricity is not constant
Changes on a time scale of 413,000 years from
0.005 to 0.058
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Discussion
Under what conditions would you expect to
glaciers covering Cleveland?
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Snowball Earth
Occurs when even the oceans at the equator or
frozen over?
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Discussion
If all of Earth is covered in ice, most of the
Sun light is reflected back into space. With so
much less energy being absorbed by the Sun, how
is it possible for Earth to ever thaw out again?
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Discussion
How could life on Earth manage to survive a
snowball Earth episode?