Another Look At Sediments Par

Another Look At Sediments Par

Another Look at Sediments

But let us now examine the ocean sediments from another aspect. If the annual amount of sediments flowing by rivers into the ocean basins and some idea of the volume of sediments on the ocean floor are known, division of the second quantity by the first should result in an approximate age of the oceans. Or to put it another way, if the annual quantity of sediments flowing into the ocean is known, this figure could be multiplied by, say, 100 million years, 4.5 billions years, or any other length of time which supposedly approximates the age of the earth, and then the average thickness of sediments on the ocean floor could be estimated.

Let us compute the thickness of sediment that should be found if the oceans were 260 million years old as deduced in accordance with the salt content. Calculations of the quantities added to the oceans by the rivers of the world will be considered first.

Clarke (11) has estimated that the rivers contribute 2.73 x 10^15 grams of dissolved solids to the sea each year. A total of 7.1 x 10^23 grams of solids would have been dissolved in the 2.6 x 10^8 years required presumably for the present sodium to accumulate. Of this total, 5 x 10^22 grams are presently in solution (12) in the ocean water.

Therefore (71.0 x 10^22 ) – (5 x 10^22 ), or 66.0 x 10^22 grams, should have gone out of solution and become part of ocean sediment. A small part of this may have been recycled due to ocean spray, etc., but the major part must still be present somewhere in the oceans.

This estimate of 66 x 10^22 grams of sediment might be checked by approaching the question from another viewpoint. Sverdrup et al reported (13) some estimates by Goldschmidt. According to Goldschmidt, for the present concentration of salt (NaCl) to accumulate in ocean solution, a total of 600 grams of rock has been weathered for each kilogram of water in the ocean. This is the basis upon which Table I was developed.

Since there are 278 kg. of water for each square centimeter of the earth’s surface, and the area of the earth’s surface is 5.1 x 10^18 cm^2 , the total weight of water equals 278 x 5.1 x 10^18 kg., or 1.42 x 10^21 kg.

Goldschmidt estimated further that for every 600 gr. of rock that have been weathered, 65% or 390 grams actually should have become available for solution in the oceans or as sediment on the ocean floor. This equals 390 x 1.42 x 10^21 grams = 5.53 x 10^23 grams.

Since 5 x 10^16 metric tons or 5 x 10^22 grams are in solution, the amount that must have become sediment equals (55.3 x 10^22) – (5 x 10^22) or 50 x 10^22 grams. This is very close to the 66 x 10^22 grams based on Clarke’s estimate of river sediments.

With the knowledge that there are presently an estimated 5 x 10^22 grams of chemicals in ocean solution and at least another 50 x 10^22 grams in sediments (based on an ocean age of 260 million years), let us determine what the ocean floor should look like. Sverdrup (14) estimated that, if the 5 x 10^22 grams of chemicals, which are presently in ocean solution, could be extracted, then a layer of salts 45 meters thick over the entire earth would result. Since the oceans cover 70.8% of the earth’s surface, this hypothetical layer would be 63.5 meters thick on the ocean floor.

Since sediments equal to a minimum of 50 x 10^22 grams would accumulate in an ocean 260 million years old, then one could expect an average sediment depth of ten times 63.5 or 635 meters or 2,100 feet (with the ocean area the same), that is, if the continents had been weathering uniformly for 260 million years.

Since the continents presumably have been here far longer (minimum 3 billions years), one could expect logically that the sediments should be far deeper than 635 meters. In fact, in that time the oceans should have almost filled up, and the land should have pretty well been eroded to level plains.

Conceivably these figures would have been changed some by presumed mountain building some hundred million years ago, but the basic concept of the oceans filling with sediment as the land masses eroded should hold true.