Just 92 elements made up the world, but the belief that were only four - earth, fire, air and water - persisted until the 19th Century. Professor Al-Khalili retraces the footsteps of the alchemists who first began to question the notion of the elements in their search for the secret of everlasting life.He reveals the red herrings and rivalries which dogged scientific progress, and explores how new approaches to splitting matter brought us both remarkable elements and the new science of chemistry.

In the last episode, Austroposeidon level trees in search of fresh foliage. A herd of Triceratops journey through a cave to find an underground clay lick. A male Carnotaurus sets the stage for an extravagant display. A female Qianzhousaurus uses an autumn storm to her advantage while hunting Corythoraptor.
A family of Edmontosaurus evade a forest fire, while an Atrociraptor and Ankylosaur reap its rewards. Juvenile Therizinosaurus attempt to climb up to a bee nest. Hatzegopteryx hunts Zalmoxes, and patrols the dense undergrowth and seaspray-battered coastline.

We are the only species on earth that cooks its food - and we are also the cleverest species on the planet. The question is: do we cook because we're clever and imaginative, or are we clever and imaginative because our ancestors discovered cooking? Horizon examines the evidence that our ancestors' changing diet and their mastery of fire prompted anatomical and neurological changes that resulted in taking us out of the trees and into the kitchen.

In the days of the Mayas, cenotes – deep, natural pits on the Yucatan peninsula - provided the only means of obtaining drinking water. But in the mythology of this advanced civilisation, these waterholes and caves were also the entrance to Xibalba – the underworld. All deceased were obliged to pass through Xibalba and wait there until they were called into heaven. It was a place in which one made sacrifices to the gods – objects of daily life, as well as bloody, human sacrifices. To this day, the relics of these acts are still in place preserved underwater for more than a thousand years. The entrance to the underworld begins at a dirty waterhole in the middle of the Mexican jungle overgrown and barely recognisable. But immediately after entry, a hall of breath-taking dimensions and beauty is revealed. As if they were sculptures, stalactites and stalagmites lend the underwater cave an almost sacred ambience. By now, one has succumbed to the fascination emanated by the world’s largest underwater cave system. We accompany four professional research divers to Yucatan – a team of specialists, able to squeeze their bodies through crevices and holes, barely larger than their bodies and who master dives that would push even the most experienced divers to their limits. With them, we penetrate worlds only a few people have ever ventured into. We encounter the remains of human victims, prehistoric fireplaces and primeval animal skeletons and undertake a dive, which takes us from the primeval forest to the open sea. We then enter Xibalba – the place of myths and the dead. In the days of the Mayas - a voyage of no return. Today, this is one of the greatest challenges one can face as a diver – the hidden world of the underwater caves of Yucatan – all filmed in 3D.

For more than 80 years, Solenopsis Invicta has been on a ceaseless march across the United States, racking up six billion dollars every year in crop damage, equipment repair, and pest control. They have conquered more than 320 million acres in 13 states and killed at least 80 people. And the invader is still on the move. Globally. Now, scientists are cracking the ant's ancient secrets to success and breeding winged assassins to hunt them down. Stunning 3D macro photography explores the secret world of the fire ant and the cutting-edge research into stopping it

On a dusty highway between Australia's most isolated city and its largest gold pit lies Coolgardie - where the arrival every three months of a new pair of foreign backpackers to work the only bar in town is a keenly anticipated event. Fresh off the plane and lured by the promise of an authentic outback experience, Finnish travellers Lina and Steph find themselves en route to a dot on the map - to pour beers, replenish depleted travel funds, and live amongst the locals. But their working holiday quickly deteriorates into a baptism of fire.
Harangued by their new boss, relentlessly pursued by booze-addled patrons, and prey to the madness and malaise of an environment as claustrophobic as it is isolated - the girls soon realise that to meet expectations out here, they'll need to do more than just serve drinks.