Below are some ‘snapshots’ of the Earth as it exists today and as it existed during the Silurian. The areas currently occupied by Britain and Ireland are shown in red.
Currently, Britain is located on the continental landmass of Eurasia, at a latitude of 54° North, approximately 6,000 kilometres north of the equator.
The continents of the world make up a pattern that we recognise from maps and globes. The surface of the Earth has not always looked like this though.
If we travelled back in time to the Silurian and could look at the Earth from space the distribution and shape of the continents would be very different.
You can see this sequence in action by looking at the animation on the next page.
410 Million Years Ago
At the end of the Silurian the continents look very different to today.
The giant southern continent, Gondwana, sits on the south pole. It is made up of continental landmass which now forms South America and Africa. Another huge continent sits over the equator stretching between the tropics and up towards the north pole - this is Laurentia.
What is now the landmass of the British Isles sits right on its south eastern coast at a latitude of approximately 20° South, 2,000 kilometres south of the equator. This continent was created by the slow closure of an ocean, called Iapetus, over 30 million years. The collision of the landmasses built chains of mountains as they were squeezed together by huge forces.
These massive changes put an end to the unique conditions that allowed the Wenlock Reef to exist.
440 Million Years Ago
Travelling even further back in time shows us how the world looked before the Iapetus Ocean closed. We can see that the British Isles actually formed from two separate continents.
Scotland and the north of Ireland are part of a large continent called Laurentia, along with North America and Greenland. Wales, southern England and southern Ireland are part of a small continent called Avalonia, at a latitude of approximately 30° South, 3,000 kilometres south of the equator.
The ocean between them, Iapetus, is slowly closing, at a rate of about 3 centimetres per year as a new ocean opens up between Avalonia and the southern continent, Gondwana. Southern Britain is heading north to meet its other half.
How do we know?
Rocks and fossils provide us with evidence that the continents have moved through time. The rocks and fossils of the British Isles are very different until the Silurian and the closure of Iapetus, after which there is a more uniform pattern of distribution.
This is a clue that different parts of the islands were separated in the past. Similarly there are fossil deposits that are identical on the eastern coast of South America and the west coast of Africa- this is a clue that they were once part of the same landmass. Look carefully at the second map and see if you can find them.