The Origin Story of Animals Is a Song of Ice and Fire

Ed Yong in The Atlantic:

Lead_960 (3)Around 717 million years ago, the Earth turned into a snowball. Most of the ocean, if not all of it, was frozen at its surface. The land, which was aggregated into one big supercontinent, was also covered in mile-thick ice. And then, everything changed. Volcanoes released enough carbon dioxide into the atmosphere to trap the sun’s heat and trigger global warming. The ice melted, and the surface of the sea reached temperatures of 120 to 140 degrees Fahrenheit. By 659 million years ago, the world had transformed from snowball to greenhouse. And just 14 million years later, the ice returned and the planet became a snowball for the second time.

This song of ice and fire was a momentous period for life on Earth. According to Jochen Brocks from the Australian National University, it liberated a flood of nutrients that permanently transformed the oceans, from a world that was dominated by bacteria to one where algae were ascendant. The algae, in turn, revolutionized the food webs in the sea, paving the way for the evolution of larger and increasingly complex organisms—like the first animals. If the Age of Algae had never dawned, we wouldn’t be here.

More here.