An Introduction to the
Marine Environment
• ~71% of the Earth is covered by salt water
• The average depth of the ocean is 3,800 meters (12,500 feet) and at its deepest depth is 36,163 feet (7,000 feet deeper than Mt.
Everest is high)
• That’s a total volume of 1,349,929,000 km3!
• The oceans constitute the largest repository of organisms on the planet
The Geography of the Ocean Basins
• The oceans (Atlantic, Pacific, Indian, Arctic, and Southern) are not distributed evenly
– Two-thirds of land found in Northern Hemisphere
– 80% of Southern Hemisphere is ocean
• A number of shallow seas are connected to the main ocean basins
• All ocean basins are inter-connected, and together constitute 1 world ocean
One World Ocean
Arctic
Ocean
Pacific Ocean
Atlantic
Ocean
Indian
Ocean
Southern Ocean http://www.gebco.net/data_and_products/gebco_world_map/images/gda_world_map_large.jpg The Ocean’s Origins
• The Earth is believed to be ~4.6 billion years old
• Originated from a tremendous debris cloud, the result of the “Big Bang”, a massive cosmic explosion which occurred 9 billion years prior
• Tremendous amounts of heat were released from decaying radioactive elements deep within the newly-assembled planet, and from gravitational compression and nearly constant asteroid impacts
The Ocean’s Origins
• So much heat was generated as the early
Earth formed that the planet was partially molten • Gravity pulled most of the heavy metals such as iron and nickel towards the hot center
• At the same time, lighter elements such as aluminum and silicon rose towards the surface, cooling into a thin crust
The Ocean’s Origins
• The cool, rigid crust rests upon a hot molten layer of mantle that is denser still than the crust above it
The Ocean’s Origins
• Due to physical and chemical differences in the rock that makes up the crust, it is thinner and thicker in some places
• Thinner = oceans
• Thicker = continents
• Ocean floor (oceanic crust) is geologically distinct from continental crust http://www.lemontree.co.nz/photograph-gallery-kaikoura-city.html Geologic differences between oceans and continents
• Oceanic crust consists of a thin, dense, dark mineral called basalt
– Rich in iron and magnesium
• Continental crust consists of a thick, light material known as granite
– Rich in sodium, potassium, calcium and aluminum
• Dense oceanic crust sinks deeper into the molten mantle, and sits even lower still since it is so thin
e.g., light continental crust
e.g., heavy oceanic crust
The Ocean’s Origins
• Eventually, the young Earth cooled enough such that water vapor (perhaps originating from impacts by icy comets) condensed and collected in the deep ocean basins
• As water collected, it dissolved minerals and salts within the rocks forming sea water
• After only 20 million years of rain, the oceans were born!
The Ocean’s Origins
• Oceanic and continental crust also differ in age
• The oldest oceanic rocks are less than 200 million years old, quite young by geological standards • Conversely, continental rocks can be as much
3.8 billion years old
• Why???
The Origin and Structure of the Ocean
Basins
• Although the Earth appears stagnant in time, evidence for geologic change is all around us
– From catastrophic earthquakes and volcanic eruptions to the slow erosion of river valleys and oceanic cliffs
– Even a glimpse at a world map provides clues for the ocean’s origins…
From the time accurate charts became available in the 1700’s, observers noticed the remarkable coincidence of shape of the
Atlantic coasts of South America and Africa
Early Evidence of Continental drift
• In 1912, Alfred Wegener proposed the theory of continental drif, the idea that all Earth’s land was in fact once joined into a single supercontinent, called Pangaea
• Discovery of coal (the fossilized remains of tropical plants) in Antarctica, and similarities in fossils across separate continents supported his theory
