For most of the Earth's history, life consisted of the simplest organisms; but then something happened that would give rise to staggering diversity, and, ultimately, life as complex as that which we see today. Scientists are still struggling to figure out just what that was.
2015 • Nature
Sagan discusses comets and asteroids as planetary impactors, giving recent examples of the Tunguska event and a lunar impact described by Canterbury monks in 1178. It moves to a description of the environment of Venus, from the previous fantastic theories of people such as Immanuel Velikovsky to the information gained by the Venera landers and its implications for Earth's greenhouse effect. The Cosmos Update highlights the connection to global warming.
Kevin explores life in orbit on board the Station. As Tim settles in to his new home he sends special reports about what it takes to live and work in space. Four hundred kilometres above the Earth, hurtling at a speed of 17,500mph, astronauts' bones and muscles waste away, the oxygen they breathe is artificially made, and they face constant threats from micrometeorites, radiation and extreme temperatures. If a medical emergency strikes, Tim is a very long way from home. In its 15-year lifetime, the International Space Station has never had a major accident. With a British astronaut in orbit, gravity-defying experiments and guest astronauts in the lecture theatre, Dr Fong shows us how to survive life in orbit.