AGE OF THE EARTH
1- ON THE BASIS OF OCEANIC SALINITY
Present day oceanic waters contain salt content but it is believed that the oceans at the time of their creation would have contained pure water, that is water without salt content. Later on rainwater after passing through continental surfaces removed salt contents from the land areas due to subaerial erosion and thus terrestrial salt used to reach the oceans through the rivers and thus oceanic water began to become saline. With the passage of time oceanic salinity continued to increase. It has been generally established on the basis of experiments and observations that about 60 percent of sodium of the oceanic salt is contributed by rivers. It has also been demonstrated that there is more or less similarity between the oceanic salt and the salt brought down by the rivers. so it is believed that rivers are the major source of oceanic salinity. Thus , there is gradual increase in the oceanic salinity because of deposition of terrestrial salt by the rivers in the oceans every year. If the total amount of oceanic salt is known and if the annual rate of increase of salinity is determined, the age of the ocean may be calculated and determined.
thus age of the oceans = total oceanic salt / annual rate of oceanic salinity
John joly calculated on the basis of series of experiments, the total amount of salt of all marine waters to be 1.26 ×10^22 g. He has further maintained that about 1.56 × 10^14 g of salt are derived from the land areas and are deposited in the oceans every year. Thus , on the basis of data of oceanic salinity as provided by Joly the age of the oceans can be calculated as follows
age of the oceans = 1.26 ×10^22 / 1.56 × 10^14 = 80,000,000 yrs
It appears, on the basis of the calculation, that world oceans were created 80 million years ago, so that earth might have been originated much earlier to the origin of the oceans.some scientists believe that the oceans were created at least 40 million after the origin of the earth. It is totally false because 200 million years old rocks of the oceanic crust have already been dated on the basis of the study of paleomagnetism.
A few scientists have tried to demonstrate correlation between the deposition of salt in the oceans and periods of mountain building at global scale.
But all these kind of assumptions are erroneous because the rate and amount of subaerial erosion is not equal everywhere. It varies both spatially and temporally. Thus rate of deposition of salt in the oceans may not be same every year. It is erroneous to believe that the land areas are the only source of oceanic salinity. It has been established that thermal convective currents bring salt to the oceanic crust which, thus, also contributes to the oceanic salinity.
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