Download The Sea Floor

Ch. 2
Part 1
The Sea Floor
Structure of The Earth and The Mid Ocean
Ridge
Objectives
1. The basic structure of the earth
2. Name the ocean basins
3. Significance of the Mid Ocean Ridge
Bang!
• The big bang
• 14-15 mya all matter and energy of space was condensed into one
point about the size of the head of a pin
• Then, for reasons unknown, it exploded
• Dust collided and formed pebbles--> rocks--> larger rocks --> etc.
• Universe is still moving away from the center
Structure of Earth
• Eventually planets were
formed
• Materials settled according
to density
• d=m/v
• Core:
• Innermost layer, dense, hot
(7200ºF)
• Liquid and solid
• Mantle:
• Semiplastic, hot
• Crust:
• Outermost layer, thin
• Oceanic and Continental
Continental vs. Oceanic Crust
• Why does oceanic sea crust lie below sea level and
continents are high and dry?
• Oceanic crust is denser than continental crust!
Measurement Activity/Lab
The Ocean Basins
• How many are there? Write them down and check
with your neighbor.
Some interesting ocean facts
• Surface area?
– 140 million square miles (71%
of earth’s surface)
• Average depth of all the
oceans?
– 12,200 ft or 3,720 m
• Deepest point?
– We’ll get there in a minute
• Highest mountain in the
world?
– Mauna Kea, HI (big island):
33,474 ft from base on ocean
floor
– 13,680 ft above sea level
Deepest and Biggest?
How did these ocean basins form?
Early Evidence
• 1620 suggested that
landmass fit together
like a puzzle
• Rocks, fossils matched
up
• 1912 continental drift
was proposed by Alfred
Wegner
• Pangea!
Pangea breakup
Wagner couldn’t explain how the continents moved
Discovery of Mid-Ocean Ridge:
The World’s Longest Mountain Range
(Over 35,000 miles long)
• Mid-ocean ridge:
– Continuous chain of submarine volcanic mountains
• Largest geological feature on earth
• Know where the Mid-Atlantic ridge (follows shape
of continents), the inverted “Y (Indian Ocean),” and
the East Pacific Rise are all located.
Trenches
• Trenches:
– Deep depressions in sea floor
– Most common in the pacific
Deepest part of ocean floor?
• Mariana Trench (MT).
How deep?
• 36,201 feet deep!
• Pressure at this depth?
– 8 tons per square inch!
• 1,580 miles long and
43 miles wide
If Mount Everest, which is the tallest point on earth at 8,850
meters (29,035 feet), were set in the Mariana Trench, there
would still be 2,183 meters (7,166 feet) of water left above it!
Discovery of MT
• 1951, British survey ship, Challenger II
– Gave its name for MT’s deepest point, “Challenger Deep.”
• More on exploration/discovery
Challenger Deep
• More on Challenger Deep
Puerto Rico Trench
• Deepest spot in the Atlantic. How deep?
• 8,400 m (5.2 miles)
• Part of the North American plate is descending under the
Carrebean plate (Puerto Rico and Virgin Islands)
What do
you notice
about these
two maps?
Check with
a neighbor
and discuss.
The Mid-Ocean Ridge: Who
Cares?
• Geological Activity:
– Earthquakes --> Ridges
– Volcanoes --> Trenches
• Red dots are volcanoes and earthquakes
– Outline of plates
Mid-Ocean Ridge: Who Cares?
• Age of sea floor
• Rock at the ridge --> young, little sediment
• Further away from ridge --> older the rock --> thicker sediment
Mid-Ocean Ridge: Who Cares?
• Magnetism
• Earth’s magnetic field periodically reverses
– About every 700,000 years (about 170 times in the last 80
million years
– Thought to be related to movement in outer core
– Compass needle points south instead of north
So what?
Mid-Ocean Ridge: Who Cares?
• Rocks contain magnetic
particles
• When molten --> act as
tiny compasses and
point north or south
• Rocks cool --> particles
frozen in place
• Form bands of rock that
alternate magnetism
• Animation
• What does this mean?
Mid-Ocean Ridge: Who Cares?
• The sea floor was NOT
formed all at once
• This is a HUGE piece
of evidence for sea
floor spreading and
plate tectonics
• Sea floor formed in
symmetric stripes that
parallel the ridge
• How does this happen?