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The Bahamas - Unique Birthplace of land - first published in the 'Nassau Guardian'.
The famous soft oolitic sand of the Bahamas was formed over thousands of years by a unique process. Photo by Ronda Cox - Tropical Kayak Tours 

Where did the Bahamas come from? How many of us have really considered this question? Seldom we do take time to examine such a lowly object as a piece of rock Yet this very rock upon which thousands of people live has, by its physical and chemical nature, determined the types of plants which are able to survive here. The plants, in their turn have determined the types of animals that have been able to exist in these islands.

The characteristics of Bahamian limestone rock are also important to Mankind. The porosity of rock provides the population with a source of water, and its chemical composition in some places provides them with a valuable natural resource.

Let us then look a little more closely at the ground beneath our feet. Our story really begins about 500 million years ago when all of today’s continents were grouped together to form a super-continent that we now call Gond­wanaland. North America, at that time, was immediately against the west coast of Africa, and what is known as the Bahamas accretionary platform did in fact overlap part of the African continental shelf. 

The comparatively new study of the way in which Continental land masses have moved is known as Plate Tectonics, the theories of which are supported by much physical evidence. Between 300 and 400 million years ago the North American continent began to move to the west as new seafloor was formed in the region of the mid Atlantic ridge. This process is still continuing and London is still moving away from New York by about one centimetre each year.

The islands of the Bahamas are the highest parts of  underwater banks. Some of the coastal rocks are actually the remains of ancient coral reefs. Photo by Ronda Cox - Tropical Kayak Tours 

It is believed that the formation of the Bahama banks began roughly 160 million years ago in what is known as the Jurassic period. Since this time marine sediments formed in various ways have been laid down in great thickness to form the Bahamas banks. A deep drilling test on Cay Sal bank bottomed at a depth of 5700 metres in Jurassic carbonates (limestone) while the Long Island drill reached bottom at roughly the same depth where basaltic lava, a type of volcanic rock, was found.  

The exact way in which this great thickness of rock was formed may never be known for certain, but much research is presently being carried out in the Bahamas, specifically in the North Andros area where sedimentary deposits are being laid down at the present time. There are two main ways by which deposits are presently being formed. Firstly a primitive invertebrate animal known as a Bryozoan - SchizoporeIIa floridana is removing dissolved salts from the water and incorporating them into its own skeletal structure. 

Secondly, there is the inorganic formation of small spherical granules called ooids; each ooid having a small nucleus surrounded by concentric layers of calcium carbonate. These nuclei may be composed of any type of rock particle that has been in suspension in the Water. The water from the deep Gulf Stream passes over the shallow Bahamas banks and experiences an increase in temperature and salinity. This results in a decrease in the solubility of calcium carbonate, hence the deposition of this substance as ooids. As the water continues across the banks two other factors continue this process of precipitation - a lower carbon dioxide content due to turbulence and the process of evaporation.

These ooids together form the substance oolite, which is presently being mined at Ocean Cay 20 miles south of Bimini. In this area there is a potential supply of approximately 20 billion tons of oolite, which is used in the manufacture of cement, in glass making, agriculture, and even in the preparation of animal foods. 

This satellite photograph clearly shows islands protruding through the surface on the wide shallow bank. The darker colour is the deep ocean.

The islands of the Bahamas resting on top of the banks appear to have been formed between 90,000 and 120 years ago from oolitic beach and dune deposits, much of which is mixed up with skeletal sands, reefs and reef derived deposits.

The land underneath the Bahamas banks has been gradually sinking for a long period of time, resulting in the great build-up in thickness. During the ice ages, however, the sea level fluctuated considerably and at one time was over 250 feet below its present level. At such times there was much erosion caused by rainwater. 

This aerial photo shows a Bluehole - a vertical submarine cave dissolved out of the soft limestone by rain thousands of years ago when the sea level was far lower than it is today.

As rain falls it absorbs a small amount of carbon dioxide and so becomes weak carbonic acid. Running down through cracks in the rock it carved out the ocean holes and underground cave systems that are so well developed in Andros. Thus, over millions of years the ocean has assisted the development of the Bahama Islands. All of our land was once beneath the sea. If the sea level were to drop 20 feet, the land area of the Bahamas would be vastly increased. However, it is a sobering thought that If it were to rise, a large proportion of our islands would disappear beneath the sea.

The famous pink beach of Harbour Island gets its colour from the many broken pieces of seashell mixed with the sand. This photo by Ronda Cox of Tropical Kayak Tours shows a variety of shells and a piece of sea urchin skeleton  mixed with the oolitic sand.

The unique fauna and flora of these islands, which we must make every effort to conserve, is a direct consequence of the method of land for­mation that has been continuing for so long here, Measured against geological time scales the existence of our wildlife seems but a fleeting moment. Already many of our species have become extinct. We must take measures to ensure that no more species join their ranks.

© R. Attrill 2000