Wants to know how old the Cayman Islands are

| 24/10/2016

What is the geological age of the Cayman Islands?

Auntie’s answer: Just the word “geology” is enough to send some people to sleep but it is in fact a fascinating area of science, and when you start looking at the history of the world in terms of millions or billions of years, it sort of puts our lives and problems into perspective. Plus, it offers us some intellectual defences from the nonsense promoted by the Young Earth creationists that the earth is less than 10,000 years old.

Scientists tell us that the Earth is about 4.5 billion years old, and the three Cayman Islands are 30 to 40 million years old. To put that in context, the dinosaurs, which went extinct 66 million years ago, were long gone before these islands made their first appearance (they apparently rose above the surface of the sea and disappeared several times over the ages).

The Cayman Islands are part of a huge submarine mountain range known as the Cayman Ridge, which extends from Central America to Cuba, bounded by very deep ocean on the north and even deeper ocean (the Cayman Trench) on the south.

The islands were formed by a series of carbonate bedrock formations separated by periods of erosion lasting millions of years. The oldest is the Brac Formation, about 25 metres thick, made up of dolomite and limestone. Then, possibly as much as 10 million years later, came the Cayman Formation, consisting of white dolomite, which is at least 130 metres thick, with five to 10 metres above the surface on Grand Cayman and 25 metres on Cayman Brac.

The Pedro Castle Formation, which is made up of dolomite and limestone and is 3 to 5 million years old, is found, as the name implies, on Grand Cayman around the Pedro Castle area where it is up to 2.5 metres thick and 15 metres above sea level, as well as in a sinkhole on the eastern tip of Grand Cayman and the western tip of Cayman Brac.

The first three formations are known as the Bluff Group. The youngest bedrock is the Ironshore Formation, which is soft fossiliferous white limestone and a variety of rock types, between two and nine metres thick. On Grand Cayman, it is found along the West Bay Peninsula and the North Sound, as well as along the shoreline of all three islands. Most of the limestone bedrock that you see was formed about 125,000 years ago, when the sea level was about six metres higher than it is now, and the oldest found through drilling is 500,000 years old.

If you are interested in the subject, I suggest you read Islands from the Sea, Geologic Stories from Cayman by Murray A. Roed, from which I have borrowed heavily, with huge apologies to the author for over-simplifications. Buy the book!


Category: Ask Auntie

Comments (6)

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  1. God says:

    If not me, then who?

  2. Anonymous says:

    If the dinosaurs became extinct before the Cayman Islands were formed, as you claim, they why do we still see dinosaurs in our LA?

    • Anonymous says:

      They are placed there by “god” to test our faith. Or our patience. Or our basic sense of modern decency.

  3. Anonymous says:

    We live in a post-factual Trump and Brexit age where the ill educated masses can ignore facts that do not suit their prejudices. Be off with your science.