The Story of Earth

The Story of Earth

In the beginning, there was no Earth, or any Sun to warm it. Our Solar System, with its glowing central star and varied planets and moons, is a relative newcomer to the cosmos—a mere 4.567 billion years old. A lot had to happen before our world could emerge from the void.

The stage was set for our planet’s birth much, much earlier, at the origin of all things—the Big Bang—about 13.7 billion years ago, by the latest estimates. That moment of creation remains the most elusive, incomprehensible, defining event in the history of the universe. It was a singularity—a transformation from nothing to something that remains beyond the purview of modern science or the logic of mathematics. If you would search for signs of a creator god in the cosmos, the Big Bang is the place to start.

In the beginning, all space and energy and matter came into existence from an unknowable void. Nothing. Then something. The concept is beyond our ability to craft metaphors. Our universe did not suddenly appear where there was only vacuum before, for before the Big Bang there was no volume and no time. Our concept of nothing implies emptiness—before the Big Bang there was nothing to be empty in.

Then in an instant, there was not just something, but everything that would ever be, all at once. Our universe assumed a volume smaller than an atom’s nucleus. That ultracompressed cosmos began as pure homogeneous energy, with no particles to spoil the perfect uniformity. Swiftly the universe expanded, though not into space or anything else outside it (there is no outside to our universe). Volume itself, still in the form of hot energy, emerged and grew. As existence expanded, it cooled. The first subatomic particles appeared a fraction of a second after the Big Bang—electrons and quarks, the unseen essence of all the solids, liquids, and gases of our world, materialized from pure energy. Soon thereafter, still within the first fraction of the first cosmic second, quarks combined in pairs and triplets to form larger particles, including the protons and neutrons that populate every atomic nucleus. Things were still ridiculously hot and remained so for about a half-million years, until the ongoing expansion eventually cooled the cosmos to a few thousand degrees—sufficiently cold for electrons to latch on to nuclei and form the first atoms. The overwhelming majority of those first atoms were hydrogen—more than 90 percent of all atoms—with a few percent helium and a trace of lithium thrown in. That mix of elements formed the first stars.

First Light

Gravity is the great engine of cosmic clumping. A hydrogen atom is a little thing, but take one atom and multiply it by ten to the sixtieth power (that’s a trillion-trillion-trillion-trillion-trillion hydrogen atoms) and they exert quite an impressive collective gravitational force on one another. Gravity pulls them inward to a common center, forming a star—a giant gas ball with epic pressures at the core. As an immense hydrogen cloud collapses, the star-forming process transforms the kinetic energy of moving atoms to the gravitational potential energy of their clustered state, which translates into heat once more—the same violent process that occurs when an asteroid impacts Earth, but with vastly more energy release.

Reprinted by arrangement with Viking, a member of Penguin Group (USA) Inc., from The Story of Earth by Robert M. Hazen.

Copyright © 2012 by Robert M. Hazen