00:00Gradually, tectonic forces formed the continents,
00:06uplifting these ancient sea beds in the process.
00:10Now, vast belts of limestone cut right across Britain,
00:15making up many of its hills and peaks.
00:18This porous stone is instrumental in the creation of caves like Titan.
00:25And so the rainfall we get here in Britain
00:28kind of percolates through that bare rock
00:31that moves through cracks and fractures into the subsurface.
00:36As water seeps into the ground,
00:39it absorbs carbon dioxide, creating carbonic acid,
00:43which eats away at the limestone,
00:45dissolving it slowly over millions of years,
00:49creating complex cave systems.
00:54And some still contain their subterranean rivers,
00:58which entice a different kind of underground explorer.
01:05Cave divers.
01:09Extreme caving at its most demanding and dangerous.
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