Earth's great paradox. For our planet to become inhabitable for life, you already need life. Ever since life emerged, microbes, plants and animals have all sculpted the planet's surface and air in the strangest of ways; fish poop creates islands; dead animals create mountains; lichen drive continents. But life also has the power to destroy our world. We are changing the climate, but we are not the first to do so. Long before us, microbes froze the planet and almost wiped out all life. The difference between us and them is we are conscious of our actions.

• Michael J. Massimino
• Will Smith
• Jaime Awe