The origin of the sand

At the time of the last ice age, the sea water level stood some 120m lower than today, fringing the edge of the continental shelf. There were beaches over there, and dunes. The sand locked up in these is radio-carbon dated to about 9,000 years old, which we will refer to as modern or Holocene sand. As the ice age ended some 6000 years ago, and the sea level rose, the beaches and dunes moved with it. By the action of waves, nearly all the sea sand within a certain size range, was swept towards the land. By about 4000 years ago, the process had ended, and the beaches and dunes were essentially where they are found today.



Note that the main component of sand is silica (silicon dioxide, SiO2) an extremely hard and slow-wearing substance, which may have originated from soil or volcanic eruptions a million years ago. Since no carbon is found inside silica, it cannot be carbon-dated. In between the sand grains, one also finds shell (calcium carbonate, CaCO3) and organic matter, which can be carbon-dated.



The latest additions to the pool of sand come from present-day rivers, but before it becomes a play ball of the water, sand is formed from rock by weathering under a layer of soil and vegetation. Although sand grains are found in sand stone and consolidated beach sand, they are not part of the earth's crust or of metamorphosed rock, nor even of mud stone. During the weathering process, the chemical composition of rock is changed, and in the process, sand is formed from dissolved silicates. Other products formed are clay and silt. Together they form the many kinds of loam. From the loams, under influence of vegetation, soils are formed.

It takes many thousands of years for rock to turn into sub soil, then top soil, then being washed into rivers, and finally ending up in the sea.



From:




Mining the Sea


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