Origin Story: A Big History of Everything

by David Christian

Two processes turned a spinning disk of matter into planets, moons, and asteroids. The first was a type of chemical sorting. Violent bursts of charged particles from the young sun, known as the solar wind, blasted lighter elements, such as hydrogen and helium, away from the inner orbits to create two distinct regions. The outer regions of the young solar system, like most of the universe, consisted mainly of the primordial elements, hydrogen and helium. But the inner regions, where the rocky planets—Mercury, Venus, Earth, and Mars—would form, lost so much hydrogen and helium that they had a rare chemical diversity. Oxygen, silicon, aluminum, and iron make up over 80 percent of Earth’s crust, with elements such as calcium, carbon, and phosphorus playing lesser roles. On Earth, hydrogen plays only a medium-size role, and helium is hardly ever sighted.