History of the oceans

History of the oceans.

A. Been there a long time

1. Earth considered to be 4.5 to 5 billion years old; oceans about a billion years younger

a. Roughly 250 million years ago, there was a single land mass, PANGAEA, with 7 major plates that made up the entire earth, and a super ocean, called PANTHALASSA, which actually is the precursor of the Pacific Ocean

b. PANGAEA broke up some 140-180 million years ago, and during the Jurassic Period, in the Age of the Dinosaurs, formed 2 super continents: LAURASIA to the north, which is now North America, Europe, and Asia; and GONDWANALAND, to the south, which is now South America, Africa, India, Australia, and Antarctica.

c. There was a shallow sea, called the SEA of TETHYS, that separated these 2 super continents.

d. Within the next 100 million years or so, these broke up to form the present continents, with movements east and west. When Africa moved north and collided with the Eurasian land mass, the SEA of TETHYS was closed off, with the remnant of that sea now being the Mediterranean Sea.

e. India moved north and collided with Asia, forming the Himalayas.

e. Thus, the present-day ocean basins were formed and in place around 80 million years ago. The Pacific Ocean is shrinking while the Atlantic Ocean is enlarging.

B. Where did the water come from, and how did it get to its present composition?

1. Fossils of marine organisms are more than 2 billion years old. Indicates that oceans at least that old.

2. The similarity of later fossils to those of present-day living forms suggest that the composition of sea water has changed very little for the last 600 million years, at least.

3. Could have been condensed out of the primitive atmosphere--"rained for 40 days and 40 nights" theory: if not taken literally, there is some truth to this, as the major mechanism by which the water was added to the oceans was by condensation from atmospheric water. However, by itself, it does not "hold water" as today's atmosphere would super saturate with water at 13,000 kilometers, which is nowhere near enough compared to the ocean's nearly 4.5 billion kilometers of water

1. Brought from outer space: there is some support for the introduction of water from outer space bodies, but again, by itself, this is probably not significant

5. Decomposition of volcanic rocks:

a. Contains up to 5% water, bound chemically.

b. If all the water from earth’s volcanic rocks that remain are removed, the total would be less than 50% of the water in the oceans.

c. Thus, incremental addition over geologic time: most widely accepted theory holds that the oceans filled up gradually, over a long period of time from the volcanic activity and decomposition of volcanic rocks, the action of hot sprigs, the heating of igneous rocks, and minor contribution from the condensation of water contained in the atmosphere.

6. Salts added from the breakdown of igneous rocks (positive ions, such as the metals of sodium, calcium, magnesium, etc.) and volcanic products (negative ions, such as the sulfides, chlorides, and the like).

7. Is it changing?

a. When the climate of earth changes significantly, the volume of water found in the oceans changes accordingly. For example, during the last ice age (more than 18,000 years ago), sea levels fell by 560 feet (180 meters), and since the beginning of the "thaw," with melting glaciers and shrinking ice sheets some 18000 years ago, the sea levels have risen 395 feet (120 meters). Should all the glaciers and ice sheets on earth melt, an unlikely scenario, the sea levels would rise another 215-230 feet (65-70 meters).

b. On a much shorter time scale, during the 1982-83 El Nino, the sea level in the western Pacific dropped by as much as 6 inches (15 cm),

c. During the last 100 years, global sea level has risen by about 1/16" (1.5 mm), probably as a result of global warming

d. During the period 1880-1980, there was an apparent global warming of 32.9 degrees Fahrenheit (18 degrees Celsius). This may have been due in part (if not predominantly) to the increase in levels of the greenhouse gas (carbon dioxide in the atmosphere). Estimates of 3.6 degrees F. or 2 degrees C. for the 21^st Century have been made (1.6 to 6.3 degrees F. or 0.9 to 3.5 degrees C). If so, sea level rise of 20 inches (50 cm) by the year 2100 is predicted (ranges of 5-38 inches, or 13-94 cm). Consider the consequence of such an event.