In astronomy, we've been looking at different kinds of light and opening up the universe a little bit more of the time. But then in 2015, the roof came off. Something happened that changed everything, the ability to see waves in space and time itself. Gravitational waves help us roll back the clock to the dawn of time, discover epic cosmic collisions, on make Earth-shaking discoveries. Gravitational waves are the biggest game changer since the invention of the telescope. We have a completely new universe to view now. A new exploration of space is just beginning.

The second episode is about how plants gain their sustenance. Sunlight is one of the essential requirements if a seed is to germinate, and Attenborough highlights the cheese plant as an example whose young shoots head for the nearest tree trunk and then climb to the top of the forest canopy, developing its leaves en route. Using sunshine, air, water and a few minerals, the leaves are, in effect, the "factories" that produce food. However, some, such as the begonia, can thrive without much light. To gain moisture, plants typically use their roots to probe underground. Trees pump water up pipes that run inside their trunks, and Attenborough observes that a sycamore can do this at the rate of 450 litres an hour — in total silence. Too much rainfall can clog up a leaf's pores, and many have specially designed 'gutters' to cope with it. However, their biggest threat is from animals, and some require extreme methods of defence, such as spines, camouflage, or poison. Some can move quickly to deter predators: the mimosa can fold its leaves instantly when touched, and the Venus flytrap eats insects by closing its leaves around its prey when triggered. Another carnivorous plant is the trumpet pitcher that snares insects when they fall into its tubular leaves. Attenborough visits Borneo to see the largest pitcher of them all, Nepenthes rajah, whose traps contain up to two litres of water and have been known to kill small rodents.

Even 2,000 years after his death, General Hannibal's battle strategies are still studied today. But of all his military feats, perhaps his greatest was leading his massive Carthaginian army of men and three-dozen elephants across the Alps and into the heartland of Rome in 218 B.C. Until now, the route they took has been a matter of dispute, but thanks to modern-day technology, geomorphologist Bill Mahaney and microbiologist Chris Allen believe they've accurately traced this ancient journey.

An intimate portrait of Malala Yousafzai, who was wounded when Taliban gunmen opened fire on her and her friends' school bus in Pakistan's Swat Valley. The then 15-year-old teenager, who had been targeted for speaking out on behalf of girls' education in her region of Swat Valley in Pakistan, was shot in the head, sparking international media outrage. An educational activist in Pakistan, Yousafzai has since emerged as a leading campaigner for the rights of children worldwide and in December 2014, became the youngest-ever Nobel Peace Prize Laureate.

The story of the longest surviving and certainly the loudest genre of rock, heavy metal. With no sign of disappearing, metal has been the most controversial and misunderstood of all rock genres. With Black Sabbath as the undisputed Godfathers, we follow their highs and lows, and, along the journey, meet Deep Purple, Judas Priest, Iron Maiden and Metallica.

Richard Rudgley goes in search of evidence of the barbarians of the dark ages, people whose names have for 1500 years been bywords for mindless brutality. The real truth about the barbarians who marched across Europe during the Dark Ages is more shocking than what you may know. Where did they come from? Who are their descendants? Are any of their techniques and inventions still used? Richard discovers the secrets of forgotten empires, and of mighty clashes throughout Europe. The art, society and cultural legacy of the barbarians are shown to have shaped and moulded the destiny of Europe even more than the Roman Empire.
In the first part of the journey through the Dark Ages we will be tracing the legacies of the Huns, Vandals and Goths, to ask whether the 'dark ages' represent a resurfacing of much older tribal lines. Sites in Austria show how sophisticated pre-Roman communities had become with evidence of stunning craftsmanship and sophisticated farming techniques which defy the image of a mindless rabble we have come to accept without challenge.