Free Creation by Adam Rutherford

the earth on which life first emerged, think about how we’ve named it. There are four geological eons spanning the earth’s 4,540-million-year existence. The most recent three names reflect our planet’s propensity for living things, all referring to stages of life. The second eon is called the Archean, which rather confusingly translates as “origins.” The third eon is the Proterozoic, roughly translating from Greek as “earlier life”; the current eon, the Phanerozoic, started around 542 million years ago and means its name “visible life.”
    But the first eon, the period from the formation of the earth up to 3.8 billion years ago, is called the Hadean, derived from Hades, the ancient Greek version of hell.
    Life does not merely inhabit this planet; it has shaped it and is part of it. Not just in the current era of man-made climate change, but all through life’s history on Earth, life has affected the rocks below our feet and the sky above us. And necessarily, the origin of life is inseparable from the fury of the formation of the earth in the first place. A picture of the Hadean earth is crucial to understanding the wild natural laboratory in which life contrived to be born. Just as the formation of our home world is an event in space, we’ll come to see how the emergence of life here is essentially a cosmic event.
    The study of the early geology is all rock-hard science, but the evidence is often both literally and metaphorically thin on the ground. It requires geological detective work with clues dotted around the planet, and off the world, too. Geology gives us clues to how the earth formed from the bits and pieces of matter floating in space around the sun. Yet it also begins to describe the world that will evolve into the host of the only living things that we know of. While our lives are built on the stability of the earth, we also are keenly aware that our planet is sporadically violently active. The solid surface (including the seafloor) is made up of seven or eight leviathan continental plates and a collection of smaller ones. These all float on the slowly flowing but solid rock of the earth’s mantle, itself encapsulating the molten core. The plates that form the crust are in constant flux, grinding and unhurriedly jiggling together. Some, such as the Pacific and North American plates, grind against each other, forcing up new land inch by inch. The subcontinent that is now India was once an island, and crunched into mainland Asia in a process that began around seventy million years ago, inching forward and crumpling up the land into the mountains of the Himalayas. These mountains will continue to grow at a rate of a few millimeters every year as the Indo-Australian plate continues to muscle its way into mainland Asia. Others plates are pulling the earth apart at the seams. The United States’ colonial expansion continues westward every day, as the coast of Hawaii grows new land at a rate of many feet per year, with molten rock gurgling up above sea level and solidifying. Earthquakes shake the land and the seabed, dislodging mountainous blocks of water that become tsunamis, such as the one that wrecked the east coast of Japan in 2011. Still, these events are currently anomalies, though they remind us that our planet is alive not just with cellular life but also with slowly flowing rock. Yet for the most part our earth is reassuringly stable.
    Not so in the past. The birth of planets is a process of summoning order from the chaos of the early solar system. Violence ensues. The sun, the star at the center of our planetary system, formed around 4.6 billion years ago as a colossal cloud of free-floating molecules collapsed under its own gravity and condensed into the huge nuclear fusion reactor that continues to heat the earth today. In the immediate aftermath, the sun sat in the center of a solar nebula, a flat disk of detritus left over by its formation but held