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MAY 2011
Oceanography Ch. # 1
Introduction to Planet Earth
70.8% of earth’s surface is covered by Oceans.
1. How many Oceans.
All interconnected, contain 97.2% of all waters.
Major Oceans:
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Pacific – largest, deepest, contains many small tropical islands.
Atlantic – about half the size and not as deep as the Pacific.
Indian – slightly smaller and not as deep as the Atlantic
Arctic -7% size of the Pacific, has a permanent sea ice layer, a few meters thick.
Southern – (Antarctic) defined by the meeting of currents – Antarctic convergence.
2. Oceans vs Seas
Seas are smaller, shallower, composed of salt water, enclosed by land and directly connected to the
oceans.
Primary seas: Red ; Mediterranean; Persian Gulf; Black ; Adriatic ; Caspian : Caribbean; Sargasso.
3. Comparing Oceans to the Continents.
Avg depth 12,234’; Mariana Trench 36,161’
Avg (Continent) elevation 2756’; Mt Everest 29,035’
Greatest relief – Pacific Ocean Mauna Kea 31,601’.
1 - # 2 Early Exploration.
Pacific navigators probably from Micronesia (small islands), Melanesia (black islands) and Polynesia
(many islands). There are no written records. Archeological evidence suggests habitation between 4000
and 5000 BC. Thor Heyerdahl proposed migration from SA. No proof.
European navigators –
Phoenicians circumnavigated Africa 590 BC.
Greek Astronomers (Pytheas) used the North star to determine Latitude. Greek scholar Erathosthenes
(in Alexandria) measured the earth’s circumference. 40,000 km vs 40,032 km. Cladius Ptolemy, an
Egyptian Greek produced a world map in 150 BC (Asia, Africa, and Europe – 29,000 km circumference).
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The Middle ages –
After the fall of the Roman Empire, the Arabs dominated world travel. The Vikins explored the Atlantic
Ocean 10th. Century climate warming. Colonized Iceland. Leif Eriksson discovered North America and
New Foundland.
5. The Age of Discovery in Europe –
Europeans explored North and South America in their search for new trade routes.
6. The Beginning of Voyaging for Science –
James Cook (1728 – 79) took soundings by lowering a weight on a line, and collected information of
reefs.
7. NOAA (National Oceanic and Atmospheric Administration – Ensures wise use of Ocean
resources . http://www.noaa.gov/
1 - # 3 The Nature of Scientific Inquiry
The Scientific method used. Science never reaches an absolute truth – never certain that all the data are
in hand. The Scientific method is used to explain most facts. (observations; hypothesis; testing; theory;
law).
1 - # 4 How were the Earth and Solar System created?
Earth is one of 8 planets , formed about 5 BYA from a nebula (an Interstellar cloud).
* The Nebular Hypothesis. Hydrogen and Helium cloud with minor amount of heavy elements.
Clumps due to gravity. Forms a Star. Condensation results in protoplanets.
* The Sun formed as the nebula collapsed and energy produced by Hydrogen fusion. Energy is
released as light and solar wind.
Proto Earth
Different from the earth today. It was larger, no ocean or life, homogenous. Heavier matter migrated
towards the center. Meanwhile, projectiles from space bombarded the surface and may have created
the moon.
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Density and Density Stratification. –
Stratification occurred as energy is released; the molten body is segregated according to density
(gravitational separation).
Earth’s Internal Structure.
Based on Chemical properties, the CORE is composed of Ni and Fe (from center – rigid to outer portion
liquid), it is 3470Km. The core is overlain by a MANTLE 2900 km thick, a rigid Silicate (inner) and plasticlike outer). The CRUST is rigid, and varies from 10 to 70 Km thick.
Based on Physical properties, it can be separated into: an inner core 1216 km, an outer core 2270 km, a
mesosphere (mantle) 2885 km, an Asthenosphere (upper mantle, plastic-like) 700 km; a lithosphere
(brittle) avg 8 – 30 km thick.
The lithosphere is a cool, rigid shell, of continental and ocean crusts and the upper mantle. It is
approximately 100 km thick. Oceanic crust is basaltic, high density (3gms/cub cm), about 8 km thick. The
continental crust is granitic , max. is about 70 km thick.
The Asthenosphere is relatively hot, plastic-like, extends to 700 km depth.
Isostatic Adjustment (vertical movement) . Oceanic crust floats deeper in the mantle than does
continental.
1 - # 5 How were the Ocean and Earth’s Atmosphere formed?
Both exhibit density stratification, both related.
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Origin of the atm.
Begins with left over gases from the nebula. Followed by out gassing. Composed of water vapor, carbon
dioxide, hydrogen and other gases, similar to gases expelled by volcanoes. Over time, it changed as a
consequence of life evolving and changes in the mantle mixing.
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Origin of the Oceans. As earth cooled, water vapor released, condensed and fell to earth.
Salinity developed as a result of dissolution , and acid rain. Eventually, a balance developed
between salt input and output .
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1 - # 6. Did Life Begin in the Ocean?
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Hypothesis # 1. Organic building blocks arrived on earth by meteors, comets, dust.
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Hypothesis # 2. Originated around hydrothermal vents
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Hypothesis # 3. Originated in certain minerals deep within the crust.
Fossil records indicate primitive bacteria on the sea floor 3.5 BYA. It is clear that the basic building blocks
for life development, were present on the early earth.
Importance of Oxygen to life.
The atm has almost 21% oxygen, which is critical for life. Life is also protected from UV radiation by an
Ozone layer in the Stratosphere. The evidence suggests that the early atm (from out gassing) was
different from the initial atm of hydrogen and helium, and different from the present (nitrogen and
oxygen). The early oxygen was used up by oxidation and there was no ozone layer. Therefore, there was
no life.
Stanley Miller’s Experiment.
Carbon dioxide, methane, ammonia, hydrogen and water were exposed to UV light and an electrical
spark. Organic molecules including amino-acid and other biologically significant compounds formed a
”prebiotic soup”.
Evolution and Natural Selection.
All living organisms has resulted from evolution by the natural selection process. These organisms have
also modified their environment.
Plants and animals evolve.
Probably the 1st. life forms were heterotrophs, which require an external food source – available from
non living organic matter.
Autotrophs (similar to anaerobic bacteria) can make their own food: evolved later. They may have also
been able to get energy from inorganic compounds associated with hydrothermal vents using
chemosynthesis.
Bacteria fossils (3.2 BYO) were discovered in deep water marine shale – supports life origin in the
absence of light. An oxygen rich atm did not appear until 2.3 BYA.
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The Oxygen crisis.
Anaerobic bacteria almost died out with the increase in oxygen in the atm. Ozone build up in the upper
atm shielded earth from UV radiation. When anaerobic bacteria is exposed to oxygen and light, they are
killed . Some bacteria adapt (Cyanobacteria).
Changes in Earth’s Environment.
The present environment results from development and evolution of plants and animals. CO2 reduced
to 0.03% (today). Free O2 increased to 21%, correlated to biodiversity. Coal, Oil and Gas formed in O2
free environments. Greenhouse effect – global warming.
1 - # 7. How Old is the Earth?
Absolute dating (from radioactive material) 4.4 BY. Relative dating from fossils. The oldest rock is 4 BY.
Oldest Mineral crystal 4.4 BY
The Geologic Time Scale. Periods are based on major extinctions, confirmed with radiometric dates.