Hours before Mehmed II launches his final assault, an ominous sight shakes both sides. Rumors of a 40-ship fleet's imminent arrival have swirled for weeks, but it's exact whereabouts remained unknown. Ottoman cannons reduced the city walls to rubble, and Venetian reinforcements arrived too late. The conquest of Constantinople ushers in a new era for the Ottoman Empire, being a dominant force in world politics for 300 years. Mehmed II, in many senses, changed the nature of world history.

Immense shoals of fish throng our shallow seas. Small fish, in turn, sustain bigger ones. The rich coastal seas are the fishing grounds of our planet and can provide an abundance of food for wildlife and humanity. The seas fringing land make up less than a tenth of the world's oceans but 90 percent of marine creatures live in coastal waters, from fearsome sharks to lowly urchins. Protecting these habitats is a battle humanity must win.

A rain forest is the richest habitat on Earth. Exactly how many species rain forests contain is unknown, but it runs into millions. And new ones are discovered every week. There are some, like the clouded leopard, we still know virtually nothing about. Although they cover just seven percent of the world's land area, jungles play a vital role in the health of the planet .
Jungles and rainforests are home to an incredible variety of species like preening birds, intelligent orangutans and remarkably ambitious ants.

The search for climate change solutions requires passion, resources and a sense of urgency -- three qualities Bill Gates clearly possesses. Bill has founded a start-up called TerraPower. After extensive computer modelling, the idea showed promise. Its new reactor greatly reduced the chance of human error. Fuelled by depleted uranium, the travelling wave reactor functions like a slow-burning candle and requires refuelling only once every decade. Bill and his team believed they had finally developed the ideal energy source, a reactor that was clean, efficient, and most importantly, safe.

Phil Jackson brings a new philosophy to the Bulls after replacing Doug Collins and takes the Bulls to the next level. He manages to not only connect on a deep level with his players, but also install the Triangle Offense, a key turning point in Chicago's dynasty.
The Bulls finally eliminate the Pistons in the 1991 Eastern Conference finals and earns a shot at an NBA title. But controversy ensues when Detroit players walk off the floor before the end of regulation without engaging in the customary postgame handshakes.

The third episode looks at anxiety and explores why it is so common. It talks to neuroscientists who explain the physiological and evolutionary basis of anxiety. Although it can help animals escape predators, anxiety can cause serious problems for human beings. It talks to sufferers of anxiety and examines the different types of anxiety people can feel. It also looks at how social media can cause anxiety.