The fourth episode sees host Neil deGrasse Tyson exploring our eternal quest to end hunger and honoring Nikolai Ivanovic Vavilov, pioneer of modern plant breeding, who risked his life for a discovery that would change the history of science. Vavilov's story is marked by both the tenacity and creativity and is particularly tragic. Interwoven into Vavilov's somber narrative are warnings and treatments of science and its ethical implications, especially when science itself comes under attack from political forces.

In 335 BC Alexander of Macedonia set off on an expedition to conqueror the world. The voyage of Alexander the Great covered more than 22,000 miles in ten years, from Greece to India and back, through some of the most difficult and unforgiving terrain. Michael Wood was hot on his trail, following, as closely as possible, in the footsteps of Alexander and the army that he drove to achieve the impossible. In this programme: the Lebanese city of Tyre, scene of Alexander's most desperate battle; the Palestinian legend of `Two-Horned Alexander'; and the Egyptian oasis of Siwa, where Alexander was proclaimed pharaoh and son of God.

This documentary attempts to make history by finding the lost city of Atlantis once and for all. Adventurer-geologist Dr. Martin Pepper sets out to prove his theory – that the true Atlantis existed on the Greek island of Santorini, and was destroyed in the biggest volcanic eruption in human history". In order to achieve his goal, Pepper will use new scientific evidence gathered using state-of-the-art sonar scans of the sea bed and microscopic analysis of the ancient landscape. One of the challenges he faces is that he must also match Santorini to a series of key clues embedded in the first ever description of Atlantis by the Greek philosopher Plato – from the lost city’s strange ring-shaped design, to the role Egyptian priests played in recording the legend in the first place. His journey will take him across the Mediterranean and out into the Atlantic Ocean. By the end of the program, he reveals the stunning findings which may pinpoint the city and show exactly what it looked like.

Fly across iridescent tropical reefs, brush through a cloud of a million jellyfish, visit an alien world where the closer you look, the more you see, where the tiniest creatures support the greatest predators... We think of reefs as exotic, distant places with little or no connection to our everyday world. Yet every reef is a living city beneath the sea with a parallel existence to ours, distant yet undeniably connected. Reefs are hotspots of biodiversity as vital to life on earth as the rain-forests. They have been shaping our shorelines, literally forming islands and mountains, for millions of years. The fossil record shows that given time they have recovered from all of earth's major extinction events. Even reefs pulverised by atomic blasts at Bikini Atoll have regenerated. Yet within our lifetime reefs have come to face their greatest threat...

Experts suspect that the dinosaurs were wiped out after a city-sized asteroid smashed into the Gulf of Mexico causing a huge crater. But until now, they haven't had any proof. In a world first, evolutionary biologist Ben Garrod joins a multi-million pound drilling expedition into the exact spot the asteroid hit to get hard evidence of the link. The team overcomes huge obstacles as it attempts to drill 1,500 metres beneath sea level to pull up rock from the Chicxulub crater. Meanwhile, paleopathologist Professor Alice Roberts travels the globe meeting top scientists and gaining exclusive access to a mass fossil graveyard in New Jersey - believed to date from the same time the asteroid hit. Alice also treks by horseback across the remote plains of Patagonia, to see if the effects of the asteroid impact could have wiped out dinosaurs across the world - almost immediately.

Discover a land as exotic as it is extraordinary. Arabia offers an in-depth understanding of one of the most fascinating lifestyles and cultures. Cross the dunes with a caravan of camels, dive in the treasure-filled Red Sea, explore the ruins of the lost city of Petra, and relive the golden age of Islamic inventions. A precious land imprinted with myths and mysteries.