Zachary Quinto explores the unpredictable and terrifying phenomenon of sinkholes to determine just what causes them. He visits a Florida man whose brother was killed when their family home was literally swallowed whole by the Earth as well as a series of sinkholes that are forming a series of caves right below the houses of a quaint suburban neighbourhood.
Whether they be a part of some biblical prophecy or further evidence of mankind's effect on our planet, he's alarmed to discover that all the same, they can strike anywhere in the world, at any time.

Planets beyond our solar system are known to astronomers as exoplanets. They are at trillions of miles from Earth and yet, it might be possible to detect a faint signature of life in them. From the light of the stars they orbit that passes through the atmosphere of an exoplanet, it is possible to capture the chemical fingerprint of the elements in that atmosphere.
The fictional world Eden is orbiting not one star, but two. The light from its twin stars powers photosynthesis, pumping more oxygen into the atmosphere than in Earth, allowing life to thrive. Grazers are constantly alert to danger, because the canopy is home to predators perfectly evolved to live among the trees. In Episode 3, another topic are fungi and the role they could play on exoplanets. Ecologist Thomas Crowther talks about the role mycelial networks play in the Rothiemurchus forest in Scotland.

Schwalmstadt Maximum Security Prison in Germany. Locked up behind the walls of this 12th-century castle are 188 of Germany's worst offenders. The prison is a fortress surrounded by a moat, and houses dangerous criminals, many of whom attend intense therapy sessions.

Discover amazing landscapes, the most amazing fights of animals on our planet, from the highest mountains to the deepest oceans, from the darkest caves to the hottest deserts with new technology. In the first episode, Sir David Attenborough explores the dangerous frontiers created by the world's coasts, where animals fight for survival amidst constant change. Cape fur seals, sea angels, lions, archer fish, flamingos and green turtles feature.

Beneath Yellowstone National Park, lies the biggest volcano on Earth. An eruption in the past was so big it plunged the earth into a volcanic winter that lasted years. A super-eruption would be more than millions of Hiroshima bombs going off all at once. It would be even worse than an asteroid impact: Entire cities lost beneath ash, people and animals crushed alive, power networks destroyed, sun dimmed across the globe, harvests failed, widespread famine. Could this nightmare really happen? We will use the latest scientific data to uncover the danger beneath us, as we see our planet like never before.

Until World War II, Latino immigration to the United States was overwhelmingly Mexican-American. Now three new waves bring large-scale immigration from Puerto Rico, Cuba, and the Dominican Republic. As the Puerto Rican government implements a historic overhaul over a million Puerto Ricans are encouraged to leave for the US mainland, to alleviate the economic pressure. A young Juanita Sanabria arrives in New York, works hard in the garment district, but encounters hostility and discrimination. Ethnic tensions explode in youth gang warfare depicted in films like West Side Story, etching the stereotype of the knife wielding Puerto Rican in the American consciousness.