Chapter 2: The Sea Floor
The oceans cover 71% of the earth’s surface.
However, more of the ocean area is located below the equator.
The Earth’s surface area above the equator - 61% ocean.
The Earth’s surface area below the equator - 80% ocean.
The oceans are classified into four large basins.
-The Pacific is the deepest and largest ocean, almost as large as all
the others combined.
-The Atlantic is a little larger than the Indian, but they are both
similar in average depth.
-The Arctic is the smallest and shallowest ocean.
From this view you can see that the Pacific, Atlantic, and Indian
Oceans are large branches of an interconnected system that
oceanographers call the world ocean.
They also refer to the continuous body of water that surrounds
Antarctica as the Southern Ocean.
There is evidence that the earth and the rest of the solar system
formed 4.5 billion years ago from a cloud of dust.
The dust was the result of a great cosmic explosion called the big bang.
The dust particles collided with each other to make larger and larger particles which
eventually built up the earth and other planets.
As the earth formed so much heat was created that the planet was probably
molten. This allowed the material to settle within the planet according to their
density.
Density is the mass of a substance per unit volume.
density = mass
volume
Internal Structure of the Earth
Core = the innermost layer composed
of a solid inner core and a
liquid outer core. It is thought
that the swirling motions of
the liquid iron rich outer core
produces the earth’s magnetic
field.
Mantle = located below the crust
it’s considered solid but
it’s very hot, near the
melting point of the rock,
so it flows almost like a
liquid, but much slower.
Crust = It is the thinnest and outer
most layer, it’s like a rigid
skin floating on top of the
mantle.
There are two types of crusts: Continental and Oceanic
The Continental and Oceanic Crusts differ in their composition.
Continental crust is made of granite, has a density of 2.7 g/cm3,
is about 20-50 km thick, and can be as old as 3.8 billion years.
Oceanic crust is made of basalt, has a density of 3.0 g/cm3, is
about 5 km thick, and is less than 200 million years old.
Early Evidence of Continental Drift
1620 Sir Francis Bacon noted that the continents on the opposite sides
of the Atlantic fit together like pieces of a puzzle.
Over the next 300 years more evidence was accumulated that the
continents were once merged.
For example coal deposits, geological formation, and fossils
on opposite sides of the Atlantic match up.
1912 Alfred Wegener proposed the first detailed hypothesis of
continental drift.
Wegener proposed that all the continents were merged into a supercontinent
180 million years ago (mya).
He called the continent Pangea.
The History of the Earth
200 million years ago a vast single
ocean named Panthalassa was
present.
After World War II the first detailed surveys of the sea floor was
conducted using sonar.
The surveys discovered the mid-ocean ridge system and trenches.
The mid-ocean ridge system = a continuous chain of volcanic
submarine mountains.
The mid-ocean ridge is displaced to one side or another by cracks
in the earths crust called transform faults.
Other characteristics of the Mid-Ocean Ridge.
- Sediment gets thicker as one moves away from them.
- Rock is older as one moves away from them.
- Magnetic anomalies.
- Earthquakes and volcanoes are associated with them.
- They are all interconnected.
Sediment Distribution
Marine sediments provide information about the earth’s history.
Two types make up most of the sediments found in the sea.
1)
Lithogenous sediment = derived from the erosion of land and/
or weathering (the physical and
chemical breakdown of rock).
2)
Biogenous sediment = made of the skeletons and shells of
marine organisms including diatoms,
radiolarians, and forams.
a.
Some biogenous sediment is made of calcium carbonate (CaCO3).
This is called calcareous ooze.
b. The other type is made of silica (SiO2) and is called
siliceous ooze.