It is 400 million years ago and the land which would later become Northern Ireland has drifted into the southern tropics.

We are in a climate latitude comparable to where Namibia in Africa is today.

And this exacerbates the 'rain shadow effect' caused by the towering Caledonian Mountains.

It was hot and dry, and rainfall was sparse and unpredictable.

Today, Death Valley in California is regarded as the hottest, driest place on the North American continent.

It too suffers from a rain shadow effect caused by the towering Sierra Nevada mountain range.

When rain bearing clouds coming in from the Pacific coastline encounter this vast mountain range they have nowhere to go but up.

The clouds are forced to rise into the cooler air at higher altitudes.

Cold air cannot hold as much moisture as warm air, so once this happens the clouds condense and fall as rain or snow on the western side of the mountain range.

The eastern side, starved of precipitation and prone to high temperatures is officially classified as a desert.

The forbidding, arid Death Valley is a good example of what Northern Ireland was like 400 million years ago.

We were, officially, a desert.