Sixty-five million years ago, a comet or asteroid larger than Mount Everest slammed into the Earth, inducing an explosion equivalent to the detonation of a hundred million hydrogen bombs. Vaporized detritus blasted through the atmosphere upon impact, falling back to Earth around the globe. Disastrous environmental consequences ensued: a giant tsunami, continent-scale wildfires, darkness, and cold, followed by sweltering greenhouse heat. When conditions returned to normal, half the plant and animal genera on Earth had perished.

This horrific chain of events is now widely accepted as...

One in a million doesn't even come close.

Not when we're talking about the odds that you would happen to be alive today, on this particular planet, hurtling through space. Almost fourteen billion years of cosmic history, over four billion years of Earth history, a couple million years of human history, the rise and fall of nations, the unbroken string of generations necessary to lead to you--it's staggering to consider. Yet behind everything in our world, from the phone in your pocket to even the force of gravity itself, lies a similarly grand procession of highly improbable...