Marine Biology / Chapter 2 – The Sea Floor

The Water Planet

The Geography of the Ocean Basins

Traditionally classified into four large basins:

1. The Pacific – deepest and largest

2. The Atlantic Ocean

3. The Indian Ocean

4. The Arctic Ocean

Connected or marginal to main basins – shallow seas

ie Mediterranean Sea, Gulf of Mexico, South China Sea.

The Structure of the Earth

• The external structure

• The internal structure

The Structure of the Earth

• Earth and solar system thought to have formed about 4.5 bya

• formed from debris left over from the “Big Bang” about 13.7 bya

• early forms entire planet probably molten

• allowed materials to settle in the planet according to their density

• Density is the mass of a substance per unit volume

• Substances of low density will float on substances o higher density.

• Density = mass/volume

The Internal Structure

• reflects planets early beginnings

• materials sank according to density – formed concentric rings

• innermost layer – core

• pressure more than 1 million greater than surface

• temp. estimated to be more than 7200o F

• Mantle – layer outside the core

• very hot; near rock melting point

• state of plastic – moves or swirls very slowly

• Crust is outer most layer

• Composition and character differ between oceanic and continental

• oceanic crust is denser and consist of basalt

• continental crust less dense and consist mainly of granite

• Both are less dense than underlying mantle.

• oceanic and Continental crust also differ in age.

• Oldest oceanic rocks are less than 200 million years old.

• Continental rocks can be as much as 3.8 billion years old.

Origin and structure of the ocean basins

• As early as 1620 – noted that coastlines of continents on opposite sides of the Atlantic fit together like pieces of a puzzle

• Cold deposits, geological formations, match up on opposite sides of the Atlantic

• Fossils on opposing coast also match

Alfred Wegner - 1912 – proposed first detailed hypothesis of continental drift

• Suggested single super continent he named Pangaea

• Proposed Pangaea began breaking the about 180 million years ago