NAME:                                  DATE:
Performance Objectives (what you need to be able to do):

1. Describe how Earth's developing atmosphere allowed life to evolve.
2. List the major components of Earth's first three atmospheres.
 

Partner Reading and Guided Study Procedure:

1. With a partner (if you need to, see instructions for Partner Reading at ) read through these Learning Objectives (what you need to know to be able to do the Performance Objectives) AND the section about epochs from the article "Astronomers Reveal First Exo Planet ID Chart" that was also handed out in class. Use the space on each page to take notes as needed.
2. As you read, cross-reference the two packets by putting the corresponding Epoch number from the article next to the objectives  below, and the the objective numbers next to each Epoch.
3. Mark the gas concentration graph (from Earth as a Planet ) with the Epochs described in the article.
4. Find the various places in your text where these objectives are discussed and write the page numbers under each objective.

    1. The processes of the atmosphere
are responsible for most of the erosion
of the land that works against the
uplift actions of the Earth's internal
processes.

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    2. The atmosphere is the layer of
gases that covers the surface of the
planet.

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    3. The atmosphere of the planet is
made of a variety of gases that cycle
through the atmosphere in a variety of
ways.

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    4. Understanding the evolution of
the atmosphere helps to understand the
importance and cycles of these gases.

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    5. If Earth's first atmosphere
(before 4 billion years before present)
was similar to that of the outer
planets of the solar system, it was
probably mostly methane CH2, and
ammonia CH4.

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    6. This early atmosphere was
probably too thin to provide any
protection from the heavy meteorite
bombardment of the time.

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    7. Earth's first atmosphere was
replaced by nitrogen N2, water vapor
H2O, and carbon dioxide CO2 from the
widespread volcanic activity that
occurred from around 4 billion to 3.5
billion ybp.

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    8. The thicker, heavier N2/CO2/H2O
air shielded the surface of the planet
from meteorites, most of which were
already cleared from Earth's orbit.

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    9. N2, CO2, H2O vapor do not provide
any protection from ultraviolet
radiation (UV) that disrupts complex
molecules such as those of living
organisms.

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    10. The atmosphere of Venus is a
good model for Earth's second
atmosphere, where high levels of CO2
keep surface temperatures extremely
high.

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    11. As the meteorite bombardment
lessened, the surface of the planet and
the early atmosphere was able to cool
enough for the H2O to condense, and rain
began to fill the low areas to form the
first oceans.

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    12. Those hot, early oceans must have
contained a vast variety of dissolved
chemicals from the land, ocean bottoms,
volcanic activity, continuous lightning
from the storms, and contributions from
meteorite impacts.

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    13. Lab experiments have imitated these
conditions, and have produced very complex
molecules similar to some of the simpler
molecules found in living organisms.

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  14. Lab experiments have demonstrated
that after hundreds of millions of
years, increasingly complex molecules
could have begun to replicate
themselves, used other molecules for
sustenance, and react to stimulus, all
of which are properties of life.

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    15. Fossil evidence of the earliest
form of living organisms indicates that
organisms similar to today's
cyanobacteria (blue-green algae) were
living in the oceans around 3.5 to 3
billion ybp.

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    16. These primitive organisms are
photosynthetic, using the energy of the
Sun to take in CO2 and H2O to form their
tissues, and releasing oxygen gas O2 as
a waste product.

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    17. The primitive cyanobacteria
must have lived deep enough in the
oceans to be shielded from UV, but
close enough to the surface to get
sunlight.

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    18. As the primitive cyanobacteria
flourished, the levels of CO2 dissolved
in the water went down, and CO2 from the
air would have dissolved into the water.

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    19. As O2 entered the water, its
high reactivity would have caused it to
combine with many of the elements
dissolved in the water, such as metals,
especially iron.

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    20. Over time, the oxygen from
photosynthetic organisms would combine
with most of the abundant iron in the
water, forming iron oxides or rust.

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    21. Solid rust particles
precipitate from water, and form dense
formations around present day
cyanobacteria.

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    22. As the oceans were cleared of
iron by the oxygen from cyanobacteria,
vast deposits of iron ore were formed
which are now being mined by people in
many areas of the world, including the
Great Lakes Region of the US.

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    23. These iron ore deposits are
nonrenewable resources because the
conditions that formed them took
millions of years and were hopefully
unique in the history of the planet.

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    24. After the easily oxidized
elements such as iron were removed from
ocean waters, the oxygen levels would
increase in the water and then in the
air as oxygen dissolved into the air
from the surface of the water.

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http://www.indiana.edu/~g105lab/1425chap11.htm

http://www.globalchange.umich.edu/globalchange1/current/lectures/first_billion_years/first_billion_years.html

http://www.geology.iastate.edu/gccourse/chem/evol/evol_discussion.html

http://homepages.wmich.edu/~cutrim/course/225/AguadoClassnotes/Chpt1/Aguadoch1.htm

http://www.livescience.com/othernews/060823_oxygen_world.html

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