Cosmos Episode 9: The Last Worlds of Planet Earth
This episode explores the palaeogeography of Earth over millions of years, and its impact on the development of life on the planet. Tyson starts by explaining that the lignin-rich trees evolved in the Carboniferous era about 300 million ago, were not edible by species at the time and would instead fall over and become carbon-dioxide-rich coal. Some 50 million years later, near the end of the Permian period, volcanic activity would burn the carbonaceous matter, releasing the carbon dioxide and acidic components, creating a sudden greenhouse gas effect that warmed the oceans and released methane from the ocean beds, all leading towards the Permian–Triassic extinction event, killing 90% of the species on Earth.
Tyson then explains on the nature of plate tectonics that would shape the landmasses of the world. Tyson explains how scientists likeAbraham Ortelius hypothesized the idea that land masses may have been connected in the past, Alfred Wegener who hypothesized the idea of a super-continent Pangaea and continental drift despite the prevailing idea of flooded land-bridges at the time, and Bruce C. Heezen and Marie Tharp who discovered the Mid-Atlantic Ridge that supported the theory of plate tectonics. Tyson describes how the landmasses of the earth lay atop themantle, which moves due to the motion and heat of the earth’s outer and inner core.
Tyson moves on to explain the asteroid impact that initiated the Cretaceous–Paleogene extinction event, leaving small mammals as the dominate species on earth. Tyson proceeds to describe more recent geologic events such as the formation of the Mediterranean Sea due to the breaking of the natural dam at the Strait of Gibraltar, and how the geologic formation of the Isthmus of Panama broke the free flow of the Atlantic Ocean into the Pacific, causing large-scale climate change such as turning the bulk of Africa from lush grasslands into arid plains and further influencing evolution towards tree-climbing mammals. Tyson further explains how the influence of other planets in the Solar System have small affects on the Earth’s spin and tilt, creating the various ice ages, and how these changes influences early human’s nomadic behavior. Tyson concludes the episode by noting how Earth’s landmasses are expected to change in the future and postulates what may be the next great extinction event.