Presenter Caroline Nolan and Dr Mike Simms of the Ulster Museum examine a snapshot of our geological past in a cliff section at Belfast Zoo.

A seam of white limestone in the rock face takes them back 70 million years to the Cretaceous period when dinosaurs roamed the Earth.

It was also a time when sea levels were at their highest which meant that large tracts of our land were underwater.

Although Northern Ireland lay in similar latitudes to where it is today, the climate was much warmer and so were the surrounding seas.

They were also rich in nutrients and filled with billions of plankton.

These warm, shallow seas provided a perfect home for microscopic organisms called coccoliths, organisms so small that a thousand of them could fit on a pin head.

As they died, their tiny shells and skeletons accumulated on the sea floor, and over time became compressed into an easily recognisable form of limestone – chalk.

And that’s where the name of this time period comes from – cretaceous is from the Latin word creta which means “chalk”.

If you look at chalk under a microscope, you can see it’s packed with the remains of these coccoliths.

Here in Northern Ireland this chalk is sometimes called Ulster white limestone.

When it originally formed it extended down into the sea basins to a thickness of at least 1000m and it would have originally covered almost the whole of Ireland.

On a much larger scale it is this type of rock which forms the white cliffs that tower above the Antrim coast road.

The same white rocks are also seen along the Causeway Coast, to the east of Limavady, at Rathlin Island, Benevenagh near Magilligan, and on the hills above west and north Belfast.