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
• 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
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: