The Vast World Ocean

14.1

Origin of the Oceans

• The earth is 4.6 billion years old• The water that created the oceans came

from:– Comets and meteorites: carry lots of water,

which transferred to Earth upon impact– Volcanism: volcanic gas has mostly water

vapor and carbon dioxide• The CO2 and other gases formed the Earth’s

atmosphere• As the Earth cooled, the water vapor condensed,

forming the oceans

The Blue Planet

• Earth is known as the “Blue Planet” because ~71% of it is covered by oceans– Average depth of the oceans: 3800 m (3.8

km)– Most of the water is found in the southern

hemisphere– All oceans are really one big body of water– 97% of the water on earth is found in the

oceans; only 3% is freshwater – Oceanography: study of Earth’s oceans

The Blue Planet cont…

• Sea level: level of the ocean’s surfaces– Sea level has risen and fallen by hundreds of

meters due to the…• Ice caps melting (H20 level rises) and glaciers

expanding (H20 level falls)

– Sea level is also affected by tectonics• TECTONICS = movement of Earth’s landmasses• Tectonics can change the level of the seafloor,

thus changing sea levels

– Currently, sea level is rising 1-2 mm/year due to melting glaciers

Geography of the Oceans

• There are 5 major Oceans:– Pacific, Atlantic, Indian, Southern, and Arctic– Largest: Pacific, Smallest: Arctic

• Sea ice: ice is less dense than water, so it floats

• SEAS = smalller than oceans, and partially or fully landlocked– All seas and oceans belong to one global

ocean, whose waters are thoroughly mixed

Mapping the Ocean Floor

• The topography of the ocean floor is as diverse as that of the continents

• Bathymetry = measurement of the ocean floor (bathos = depth, metry = measurement)

• Began with the ship “Challenger” in the 1870’s– Although today’s technology is much more

sophisticated!!!

Mapping the Ocean Floor cont…• SONAR was first used in the 1920’s to

map the seafloor features of the S. Atlantic ocean

• SONAR = SOund NAvigation and Ranging– Uses echoes of sound, return time, and

velocity of sound in water to measure depth– Velocity of sound in water = 1500 m/s

SONAR

– Equation: (Time for echo return) x (Velocity

of sound in water) /2

Problem: It takes 4 seconds for an echo to return. How deep is the ocean?

(4 s x 1500m/s)/2 =

3000 meters

Mapping the Ocean Floor cont…

– SIDE-SCAN SONAR = aim SONAR at angles

– It is used to map underwater hills, trenches, ridges, etc…

• Satellites continually gather information about the ocean floor– Data has shown that the ocean surface is not

totally flat...– Why?? Gravity attracts water toward regions

where massive ocean floor features occur. Mountains/Ridges have elevated water. Trenches have depressions

Side Scanning SONAR

Submersibles• Submersibles (small underwater crafts)

give us much data– Manned crafts:

• Trieste- Jacques Piccard (1960)– went to Mariana Trench (10,912 m) – deepest trench in

the world

• Alvin- 4000 m• Sea Cliff II- 6000 m

– Unmanned crafts: – called AUVs

(autonomous underwater vehicles)