Believe it or not, even the last ice age had a profound influence in forming the Bahama Islands. For about 2 million years there were repeated cycles of glacial advances and retreats. The Earth froze and then the ice melted and then it did it all over again. It is estimated that as much as 30% of the Earth’s surface was covered by ice during glacial advances.
Even though, the newly formed island platforms may or may not have been totally covered by ice, the formation of increasingly enormous ice sheets in other parts of the Earth, had major influences on shaping the Bahama platform.
Why was this? How could massive ice blocks in other parts of the world shape the islands of the Bahamas? It’s pretty simple really; it’s all about water…
During periods of glacial advance, increasing amounts of the Earth’s water was frozen for thousands and thousands of years at a time. This freezing of more water in one area caused there to be that much less water in other places. This process of nature caused sea levels to drop in many places. One of these many places, where sea levels dropped, was in and around the islands of the Bahamas.
This drop in sea levels exposed more of the Bahama platform. It is estimated that sea levels fell by some 120 meters or 400 feet during one glacial advance and by just under 120 meters during the last ice advancement.
After almost 200,000,000 million years, we had the hard limestone rock of islands, but The Bahamas needed one more of nature’s elements to help it along…
Western Atlantic islands, like the Bahamas, are composed mostly of limestone. This type of rock erodes easily and does not contain or contribute to making the nutrient rich soil needed for lush vegetation.
The Bahama Islands needed one more element of nature to help it along. We now had land above sea level. We had the beautiful sea filled with marine life of all descriptions. But, we needed one more thing to help make the picture complete. So nature, in the form of the Tradewinds, came to help us along.
The Tradewinds are a circulation of air that starts with rising air in tropics. Incredibly, through these winds, the Bahama Islands are linked with the great continent of Africa. The wind blows easterly rising from the tropics towards Europe and Africa and westerly from the tip of Spain and north-west Africa back to The Bahamas. The westerly Tradewinds carried with them very fine clays, silts, and sands called ‘African Dust’ from the deserts of northern Africa to the Bahamas. This ‘African Dust’ was deposited during rain showers. These winds, over the next three million years, moved the fine marine sediments into a series of high sand dunes across the hard limestone rock, to form the land that we see now.
Geologists have concluded, through ground investigation, that the prehistoric soil in the Bahamas developed mostly from ‘African dust’. If it were not for this ‘African Dust’ the Bahamas as well as the other islands of the western Atlantic, would have otherwise lacked sufficient fertile land for crops like pineapples and sugar cane to flourish.
In 2007, Geologists studying soils from Barbados, the Florida Keys and the Bahamas found levels of scandium, chromium, thorium and zirconium in the soil. These elements acted as fingerprints, to reveal where the soil originated. They found that 60 percent of the soils in the Florida Keys and 40 percent of those in the Bahamas are African dust.
Pools of crystals containing African Dust found in Ralph’s Cave, Ralph’s Blue Hole, ABACO, Bahamas
|In 2010, a team from National Geographic, collected samples of ancient African Dust, that blew over from the Sahara a million of years ago, in the underwater caves of Ralph’s Blue Hole in Abaco.|
A glimpse into the future by looking back at the land
There will be significant implications and consequences for the Islands and its future inhabitants simply from looking back at the land and how it was formed. The formation holds a peek into a time to come. A time when people will come to depend on the land for their homes, for food and their livelihood.
All Bahamian land is limestone. It is a very common type of sedimentary rock found around the world. But where we find limestone, its characteristics are not known for being particularly favorable to agriculture. In other words, it does not do particularly well for growing things.
Relatively speaking the Bahamas limestone is young and very pure in the large amounts of calcium carbonate it contains. The limestone rock of the Bahamas is not a mix of different types of rock, like mineral rich igneous or metamorphic rock, the islands are mainly composed of a single component – limestone. This rock purity means only calcium carbonate is available to the plants and trees that grow on it. Most other types of rock, like the ones found near volcanic areas and others, contain a varied mix of nutrients that release these minerals into top layer soil through weathering. But limestone doesn’t. When limestone breaks down, it leaves nothing behind by way of nutrients.
Bahamian limestone also has a high alkaline level around 7.5 to 8.5. Anything higher than a Ph7 is a disadvantage because it limits the ability of plants to absorb water[i]. And as if that were not enough to challenge the future inhabitants of the islands, limestone also dissolves in water. This means that rather than breaking down into smaller bits when it comes into constant contact with seas and rain, it just simply dissolves leaving holes and craters. For plants and trees that grown on this type of land, they tend to wash away easily as the rock beneath it erodes and dissolves.
The black soils are the most plentiful soils and in the future would form the basis for much of the farming in the islands. But farmers would need to clear acres of bush by burning to get access to the soil. The burning would add nutrients to the soil. But as future inhabitants would find, this method of cultivation would be short-term, often only good for a year and then the bush needed to grow back before the process could be repeated. This would mean that farmers might have one good year of bountiful and plentiful crops like cotton, potatoes or oranges then several bad ones, where nothing plentiful would grow[iv]. The white soils are essentially sand dunes. While this type of soil has depth, it is sediment, not rich crop growing soil and so has limited nutrients and minerals needed for cultivating large amounts of fruits and vegetables. The red soils are the unusual part of the mix as they are, as we have seen, blown in from the Saraha in North Africa. They are essentially a compound of minerals commonly referred to as laterite, because of its brilliant red colour. However because of the long journey this soil would make across the ocean and the seas to the Bahamas, though highly producing for a time, red soil would eventually fall silent, giving nothing for long periods to come once it began to be cultivated commercially[v].
[i] Sealey, N. Soil and Land Resources of the Bahamas http://www.iica.int/Eng/regiones/caribe/bahamas/ATT/Documents/Soil%20and%20Land%20Resources.pdf [Accessed 30th January 2012]
[ii] Hunnington, E., and Milford, H., (1915) Civilisation and Climate, Yale University Press p.29
[iii] Willias, J.C. (1922) Age and Area: A Study in Geographical Distribution and Origin of Species Cambridge p65
[iv] Derevenski, Joanna S., (2000) Children and Material Culture, Routledge, p.108 discusses slave plantation life in the Bahamas and how on some plantations, like the Wylly, 1818, the slaves had nothing to do as there was no planting going on due to the poor soil for growing. Slaves were encouraged to work for themselves and their diet was heavy in conch and fish from the sea as plantings were very sparce.
[v] Ibid p.30