Satellite pictures always reveal the dominance of the blue color corresponding to the relative size of the earth surface covered by the oceans (71 %).
As a result, man's development is invariably tied to the oceans:
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60% of humans live approximately 1 mile from an ocean.
- The oceans were the first home of all living organisms.
- The oceans has been a major supplier of oxygen in the atmosphere.
- 2 % of human food is seafood.
- 35% of oil and natural gas is now mined from marine locations.
- The oceans have been a major medium of transportation, and to a lesser extent recreation.
- On the regressive side, the oceans has always been a massive dump site for human wastes.
SOME BASIC FEATURES
There are 4 geographic oceans - Pacific, Atlantic, Indian, and Arctic. However, oceanographers have delineated a 5th ocean in the recent past based on ocean water properties - Antarctic Ocean. The salty ocean water in each ocean is held within bowl-shaped mega features called ocean basins. These ocean basins are all interconnected.
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In addition, there are marginal bodies of ocean water partially sorrounded by land called seas. These coastal bodies of water adjoining the ocean basins were the first familiar marine areas known to man. Seawater may be more, less, or as salty as average ocean water. The Caspian Sea is a freshwater lake.
Familiar examples of seas are:
- Yellow/Red/Black Sea,
- Caribbean Sea,
- Gulf of Mexico,
- Mediterranean Sea,
- Baltic Sea,
- North Sea,
- Sea of Japan,
- South China Sea, etc.
AREA:
71% of theEarth's surface. In the northern hemisphere (NH), area covered is 61%, whereas it is 81% in the southern hemisphere (SH). In terms of area, the order from largest to smallest is Pacific, Atlantic, Indian, Antarctic, and Arctic oceans.
AVERAGE DEPTH:
approximately 4.0 km below mean sea level (msl), whereas the average elevation of the continents is only 0.85 km above msl.
AVERAGE TEMPERATURE:
4 degrees Celcius.
ORIGIN OF THE OCEANS
The nebular theory is the most popular explanation for the Solar System's (and Earth's) origin. The theory proposes that stars and other known cosmic bodies began as a large mass of gas and dust called nebula. Nebulas are the diffused areas of a larger collection of organized matter and energy known as a galaxy.
According to ther theory, about 5 billion years (by) ago, the an area of the Earth's galaxy, the Milky Way, was hit by a supernova explosion. A dense area of matter within the nebula absorbed some of most of the heavy elements from the explosion. The kinetic energy from the explosion caused the dense area to rotate rapidly. The spining motion caused an increase in gravitation which pulled more material into the dense, spinning area.
The compression of the material generated heat. As temperature increased, nuclear reactions increased. The dense, spinning mass became the Sun, and the peripheral materials clustered into the 9 known planets such as the Earth. Over 1 billion years, the young, hot earth (and other planets in our solar system (SS)) continued to attract nearby matter and grow.
As the earth grew, it became hotter from:
- Meteor Impacts
- Radioactive Decay, and
- Gravitational Compression.
The Earth gradually became density-stratified as the most abundant heavier elements began to sink to the earth's center. The accumulation of these heavier elements formed the Earth's core. The elements formed a gradation all the way to the Earth's surface with lighter, and lighter elements occupying a soft, solid surface below a primitive atmosphere by 3.8 by ago. The soft, solid surface cooled gradually forming rocky depressions called ocean basins.
This primitive atmosphere was dense (very cloudy), hot, and constantly receiving a steady supply of gases from the earth's interior through cracks and vents - a process known as volcanic outgassing. The common gases believed to have composed the primitive atmosphere were: water vapor, carbon dioxide, ammonia, methane, nitrogen, hydrogen, and hydrogen chloride. But there was no free oxygen in the atmosphere at this time.
As the earth surface continued to cool down, these gases condensed into hot, steamy rain that gradually began to fill the ocean basins approximately 3.6 by ago. The hot water constantly dissolved salts from the volcanic rocks to make the ocean water salty. Modern scientists also believed that water was imported to Earth by an early period of heavy bombardment via comets -- known to be made up of ice and rocks. This type of water is known as cosmic water.
ORIGIN OF LIFE
By most acounts, it is most likely that life first appeared in the primitive oceans about 3.5 by ago, based on the oldest confirmed fossil - a primitive bacteria colony called stromatolites. It is no surprise that most living organisms have remnants of ocean water within and outside our cells. Even embryonic fluid in pregnant women has a composition that is similar to ocean water.
However, no one understands the process of biosynthesis - the leap from biological molecules to self-sustaining cells. Some scientist have speculated that this "miracle" must have happened on ocean floors near hydrothermal vents. These organisms are believed to have been chemosynthetic, and single-celled that obtained energy from simple chemical compounds from their natural sorroundings.
But by 2.8 by ago (700 my later), photosynthetic single-celled organisms began to appear. This was a major milestone because these "new" creatures began to bubble oxygen into the atmosphere. At this time, the primitive atmosphere must have been less cloudy, and hence more transparent to the Sun's rays. The addition of oxygen in sufficient quantities paved the way for land (terrestrial) organisms to evolve, as high frequency volcanic activities began to form elevated areas above ocean water.
Some light was shed on the origin of life from an experiment conducted by Urey and Miller in the 1950s. These scientists mixed primitive atmospheric gases in a glass flask, and energized the mixture by electrical sparks, and heat. The result was a dark, brown soup containing common organic molecules like amino acids, nucleic acids, and simple sugars. Subsequently, several other scientists repeated this experiment and encountered the similar results.
What did this result explain?
It certainly did not explain the origin of life on earth. But the most reasonable meaning one can derive from the Miller-Urey results is that the conditions that can support life was already present at a relatively early time in the planet's history. It did not explain how these common molecules found in living organisms could assemble into a self-sustaining cell. One should be reminded that conditions on Earth has changed slowly, and is always changing slowly.
