Cosmos: The Lost Worlds of Planet Earth

This episode of Cosmos really has something to say as we revisit the Halls of Extinction (previously seen in the second programme of the series, Some of the Things that Molecules do) to examine the Permian extinction of 300 million years ago. Volcanic eruptions released carbon dioxide and methane, causing global warming that wiped out 9 out of every 10 species on the planet.

The animated sequence - a short one in comparison to others in the series - is on Alfred Wegener. In his time geologists believed that there were once land bridges across the Atlantic Ocean, long since vanished, to explain how fossils of the sames species could be found on both sides even with an ocean separating them. Wegener took the evidence, worked backwards and came up with the idea of continental drift and called the original supercontinent he theorised "Pangaea."

His continental drift views were not accepted in his time and he became a laughing stock and a pariah in his field, and one day in 1930 he disappeared while on an Arctic expedition. In 1952 Wegener's ideas were vindicated by Marie Tharp who mapped the mid-Atlantic floor.

Tyson takes the Ship of the Imagination down into the Marianas Trench to look at the animals that live even down there in the deepest place on Earth, but this isn't a David Attenborough series so he soon moves on, deeper, below the crust of the Earth to look at the core and mantle, explaining how continental drift occurs. The flow from one subject to another feels natural, even though they could have been covered without any link to one another.

Another extinction event, most certainly better known than the Permian one, is the asteroid that wiped out the dinosaurs but gave the mammals the chance to become dominant on Earth. Tyson then takes us from that event to the evolution of man, showing how some (less well known) random events had consequences that shaped the course of that evolution: the continental drift that brought North and South America together changed the ocean currents in that part of the world, which had a knock on effect on the ocean currents around Africa. The African climate became drier, and tree-dwelling animals came down from the dying-out trees to the Savannah, where to compete with the other ground animals they evolved to use tools (monoliths may, or may not, have helped with that).

The gravitational effects of Venus and Jupiter had tiny but incremental effects on the Earth's tilt and orbit over millions of years, resulting in the ice ages. We are now in a warm interval between ice ages, due to last for another 50,000 years.

And now the various strands of this programme come together as Tyson warns of the dangers of man-made global warming and climate change, accelerating, changing or amplifying the natural (but very slow) changes the Earth undergoes over time. He points to an empty corridor in  the Halls of Extinction and says we don't know when or how it will be filled. Maybe an obvious message to some of us, but a powerful one nonetheless.