Forces of Nature

We can't directly see the forces that govern Earth, but we can see their shadows in the shapes of nature that surround us. If we understand why these shapes exist, we can understand the rules that bind the entire universe. Gravity is the great sculptor of our planet. Every two years, in Tarragona, Spain, towns from across the region compete to build the highest, most complex human towers. The shapes formed by hundreds of people in each team as they create towers up to 10 people high are beautiful but also carefully designed to combat the power of Earth's gravity. Every year hundreds of icebergs, some of Earth's most spectacular natural sculptures, break away from the Greenland glacier and drift into the Atlantic, causing a hazard to shipping and oil platforms. Unlike any other fluid on Earth, water expands as it freezes. Deep within the iceberg, electromagnetism, the force of nature that bonds atoms and molecules together, causes the water molecules to join in a lattice of billions of hexagons. The balance between the forces of gravity and electromagnetism create Earth's epic landscapes but our planet is unique in the Solar System - and perhaps the entire Universe because it has one thing that creates an even richer diversity of shapes: life. High in the Himalayas of Nepal, the Gurung people of Annapurna head out from their villages to harvest honey from the largest honeybees in the world. In the Florida Everglades we discover another of nature's shapes, this time forged by evolution. The Florida manatee is the most rotund of all manatees. As it lives furthest north, in cooler waters than its Caribbean cousins, it has developed a unique body shape. There is one rule of shape that is found across the animal kingdom - bilateral symmetry - a body with a left and a right and a head with sense organs. In South Korea we meet the Haenyo of Jeju Island, a proud group of women, many of them older ladies, who supplement their income by free-diving for food.

The forces of nature make Earth a restless planet but they also made it a home for life. To understand how something so complex could emerge from a barren rock we first need to understand what our planet is made of. In this episode, we look at the elements. On the Kawah Ijen volcano in Indonesia, firefighters battle to protect the purity of the sulfur that boils to the surface. Beneath the green grass of the Great Rift Valley in Tanzania, rock is stained red by iron because elements react and combine with each other to create molecules. In a cave system in the Dominican Republic we see, a halocline, created by water's power to dissolve. In Italy, Alpine ibex make an astonishing climb up the near-vertical face of the Cingino Dam to lick essential salts and minerals that have evaporated on the rocky wall. The chemistry of life, the reactions between Earth's elements, use and create energy. Off the coast of Toyama Bay in Japan each spring, millions of firefly squid rise up from the deep ocean to spawn, their bodies glowing with a dazzling pattern of blue lights created by life's alchemy. But it is another piece of chemistry that we think was the first step in our planet's journey from ball of rock to a living world. In a fjord off the coast of iceland, a hydrothermal vent soars up from the sea bed. A simple experiment shows how this water creates power. It is the same mechanism that is found throughout the living world and powers every cell in our body. This leads to the intriguing possibility that our most ancient ancestor wasn't a living thing at all but a hydrothermal vent at the bottom of an ancient ocean.

Earth is painted with stunning colors. By understanding how those colors are created and what they mean, we can look out into the Universe and look for other planets just as vibrant and colorful as our own. The colors we see are created by the way the light energy from the Sun interacts with whatever it strikes. The signature color of our planet is the blue of its oceans but the unique way water interacts with sunlight to create this color, also explains why, each year, thousands of humpback whales congregate in the waters off the Dominican Republic. Earth is swathed in another color, the color of life itself: the green of the pigment chlorophyll, which absorbs some of the color energy of light, and reflects others back out into our eyes. Plants have evolved to harvest the light energy of the Sun using color. But life has also evolved to sense and use color. In Papua New Guinea just as the spectacular Birds of Paradise use color to attract a mate, the richly colored feathers are highly prized by the local human males, for much the same reason. Earth has colored itself richly and as humans we see beauty in the colors it displays. None more so than in the Northern Lights of the Arctic Circle. Like all colors, the green and purple of the night sky is a code, it has meaning. Each color is the result of atmospheric gases energized by the solar wind blasting out from the Sun. Green is created by the oxygen of the air we breathe, purple by nitrogen. Each element has its own unique color signature. With this knowledge we have started to explore the furthest corners of the Universe as alien photons bring the color signatures of far distant stars and planets to Earth.

The forces of nature have kept Earth on the move since it was formed billions of years ago and its epic journey through space shapes all our lives. Earth is spinning at an incredible speed, whilst at the same time orbiting the sun and yet we are not aware of this motion. In this episode, we take to the air in one of the world's most advanced aircraft, a Eurofighter Typhoon, in a carefully planned operation to outpace the spin of the Earth and for a few seconds stop the sun in it in tracks, hanging just on the horizon. In the Tropics, Earth's spin can set tropical storms in motion and these sometimes turn into hurricanes or typhoons. Earth moves through space with its constant companion, the Moon. A few times a year, the Earth, Moon and Sun align perfectly and the combined gravitational pull creates extreme tides. Few are more extreme than the tidal bore that surges up the Amazon River in Brazil - the Pororoca. Whilst the locals flee to escape the destructive power of this ferocious wall of water, one man seeks it out. We are all unwitting passengers on an epic journey through space as the Earth spins and orbits on its tilted axis. And humans mark the passage through the year with rituals like the Ardia, an epic horse race, held each year in the town of Sedilo, on Sardinia. With each passing year, we have travelled not only another 550 million miles around the Sun, but our entire Solar System is also moving with the spin of our galaxy, the Milky Way. Each year on Earth takes us another 4.5 billion miles through space. We are all space travelers, riding our own spaceship, Earth.