EAS100 Lecture 17: EAS 201 - End of Cryosphere & Intro to Oceans

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EAS 201: Lecture 17
February 13, 2019
Lecture notes & images borrowed from Karlis Muehlenbachs’ slides February 13, 2019.
Can analyze rocks and determine where they originated which can again lead back to
the theory of continental drift (in one area can find rocks from Canadian shield or
elsewhere).
Long periods of time + a sustained positive mass balance ice sheet creation.
Only ~ 10% of Earth’s history is characterized by an active cryosphere & the presence of
glaciers & associated deposits.
o If a planet has more ice, it will reflect more light cooler overall temperatures.
Snowball Earth Hypothesis:
o Continents were assembled, ice
started to grow and reached a
point that there was so much ice
the Earth temperature dropped
causing higher freezing (planet
covered w/ ice).
o Trapped/built up CO2 gases from
volcanoes under the ice will lead
to a super greenhouse effect (“Hothouse Earth).
Ocean Basins & Ocean Water:
o Seawater covers 70.8% of Earth’s surface.
o Most of it is contained in 3 interconnected basins; Pacific, Atlantic, & Indian
Oceans (these plus the Southern Ocean make up the world ocean”).
o There are varying depths all along the sea floor.
There are a lot of areas that are of similar depth (~4 km).
Marianas Trench near Guam is deepest ocean depth (10,924 m).
o Some of the oldest rocks that have been found show evidence of being product
of liquid water.
Suggests that ancient Earth had oceans existing even though some
hypothesize Earth would have been frozen due to distance from Sun &
ancient Sun being less hot.
o Underwater volcanic features: Pillow Basalts.
Volcanic igneous rock formed when lava of basaltic composition is
erupted underwater.
o Oxygen isotopes in zircons suggest the ocean may be 4.4 billion years old.
Where did the water come from?
o Carbonaceous Chondrites contain water as hydrous minerals, suggests some
water originated from accretion & volcanic steam.
o Icy Comets bombarded ancient Earth and brought w/ them frozen water.
Ocean Water:
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