HAVE you ever wondered why Brighton beach is covered in pebbles rather than golden sand?

The history of the beach and its geological secrets will be explained in the first episode of this year’s Royal Institution Christmas Lectures, which airs on BBC4 at 8pm tonight.

Geologist and adventurer Professor Chris Jackson, of Imperial College London, is hosting the presentation, which explores how our planet’s oldest rocks and fossils show radical climate changes throughout history.

As part of his demonstration, Prof Jackson explains how Brighton beach was set in stone by processes which took place millions of years ago, as the UK drifted northwards from low to high latitudes on top of a giant tectonic plate.

He said: “Large parts of Sussex’s cliffs are made of the easily-eroded chalk rock which originally formed on the seafloor as lime mud about 90 million years ago.

“As the layers of lime mud built up and the seafloor subsided, the lime mud turned to chalk, before being uplifted from deep within the Earth to be exposed as the now-famous chalk cliffs.

“Natural erosion by rain, wind, and waves means this soft rock breaks down and dissolves or turns to mud rather than to sand, gradually being washed away.”

Prof Jackson added that trapped within the chalk are flint-like pebbles which are much harder to erode and transport.

He said: “Some rocks, like sandstone and mudstone, are easily eroded and break down due to the action of waves, forming sandy beaches.

“Other rock types, like chert - a type of flint-like, silica-rich rock found within softer rocks like chalk - do not break down so readily.

“They can withstand intense wave action, although they become very round to form the large pebbles that characterise many of the beaches on the south coast of England.”

The episode, which is titled Engine Earth, will also show how human activity is impacting on the environment and our beaches.

While increased storm activity due to global warming is causing cliffs to crumble at a faster rate, viewers may be surprised to learn that beach groynes are also contributing to the erosion of coastlines in Sussex and across the UK.

Prof Jackson said: “The groynes serve a specific purpose but they are unnatural features that try, and often fail, to stop a natural process.

“The result is often enhanced cliff-line erosion and land loss along other parts of the coastline. By influencing climate dynamics and the natural coastal process, we impact biodiversity.

“So yes, we all love a nice beach for our summer holiday, but it might be coming at a cost.”

Prof Jackson will discuss beaches as part of a wider talk on climate changes throughout history, which he says are driven by the amount of carbon dioxide in the atmosphere.

He said: “For billions of years the level of carbon dioxide in the air has been controlled by Earth’s finely balanced tectonic system, but for the first time, humans are tipping this balance.”

The lecture is on BBC4 tonight at 8pm.