In the beds of giant kelp along the California coast, this balance is vividly illustrated. Giant kelp is a nursery for thousands of species of fish and aquatic life. But 50 years ago it was in decline as a result of an imbalance between two key players: sea otters and sea urchins. Urchins have a voracious appetite for kelp, and because otters had been hunted to the brink of extinction for their fur, the urchin population exploded. Before long, much of the seafloor was bare, razed of its kelp. Then, conservation groups began reintroducing sea otters to coastal waters where their favorite food, the urchins, were in abundance. A sea otter bobs to the surface, rolls over, cracks an urchin shell and eats the contents within. With the return of the otter, the kelp forests flourished—along with all the species that depend on them.

In the tropical rain forest, the biodiversity of the planet reaches its peak. The sheer number of organisms it takes to make a system healthy is greater here than anywhere else: howler monkeys swing from branches; macaws, gekkos, toucans, beetles, tapirs, and leaf-cutter ants create a symphony of color and sound. Whether in the soil, the ocean, or in the tropical forest, there is a strong connection between living things and their habitats. Diversity is life's strategy of survival.

But there is a problem. As we humans alter more and more of the Earth, animals are losing many of the places in which they live. We see an animation of the entire Earth turning slowly in space. The forests are shrinking. Humans began to change the planet 6,000 years ago. At that time, 34% of the Earth's surface was covered by forest. With the advent of the Industrial Revolution, human impacts became visible. As the Earth spreads out before us, we see green receding slowly across Asia, Europe, Africa, then the Americas. In the past 50 years, the greatest changes have taken place. Today, only 12% of the Earth's surface is covered by forests, and we are just beginning to realize how many life forms we may be losing.

Contemporary scientists are working against time to determine how much life we have lost, and how much still remains unknown. We fly over dazzling collections of rare butterflies, beetles, and orchids. So far, scientists have classified nearly 2 million species, but this is only a fraction of what exists: some researchers believe there may be between 10 and 40 million species on Earth.

But the story is far from over. There are still places on Earth where we can see the natural world undisturbed by human beings, where life adapts and diversifies as it has since time began. A young botanist, Fabián Michelangeli of the American Museum of Natural History, is preparing to join a Rapid Assessment Program on an expedition to one of the most mysterious and unexplored places on Earth: the table mountains of southern Venezuela that have come to be known as the "Lost World." These mountains inspired Conan Doyle's famous novel of the same name, featuring intrepid explorers who discover a land of living dinosaurs.

The expedition is being organized in Caracas, the capital city of Venezuela, by Fabián's good friend and fellow biologist, Margarita Lampo, whose specialty is amphibians. All over the world, these creatures are declining in population. We see Margarita preparing to leave for the expedition, planning final details with the third member of the expedition, Celsi Senaris, and waving goodbye to her family. Her small son watches as she leaves, waving his toy plane from the balcony. In a dissolve the toy becomes a DC-3 flying above rain forest that stretches to the horizon.




Landing at Canaima, the three scientists and their guide load into a jeep to travel across the vast grasslands of the Gran Sabana. The next morning, at first light, the team sets off with an Indian boatman in a dugout canoe. When the river becomes too shallow, they begin to hike through the rain forest, surveying the life they see: coatimundis, spider monkeys, guacamayos, even puma tracks, indications of a rich biodiversity. High above and in front of the team loom the table mountains, or tepuis: thousands of feet of vertical cliff wrapped at the base in dense rain forest.