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