第35页 The reverend Evan's Universe

"There's something satisfying, I think," Evans said, "about the idea of light traveling for millions of years through space and just at the right moment as it reaches Earth someone looks at the right bit of sky and sees it. It just seems right that an event of that magnitude should be witnessed."

According to Hoyle's theory, an exploding star would generate enough heat to create all the new elements and spray them into the cosmos where they would form gaseous - the interstellar medium as it is known-that could eventually coalesce into new solar systems. With the new theories arises it became possible at last to construct plausible scenarios for how we got here. What we now think we know is this: 

About 4.6billion years ago, a great swirl of gas and dust some 15 billion miles across accumulated in space where we are now and began to aggregate. Virtually all of it -99.9 percent of the mass of the solar system went to make the Sun. Out of the floating material that was leftover, two static forces. This was the moment of conception for our planet. All over the inchoate solar system, the same was happening. Colliding dust grains formed larger and larger clumps. Eventually the clumps grew large enough to be called planetesimals. As these endlessly bumped and collided,they fractured or split or recombined in endless random permutations, but in every encounter there was a winner, and some of the winner grew big enough to dominate the orbit around which they traveled. 

It all happened remarkably quickly. To grow from a tiny cluster of grains to a baby planet some hundreds of miles across is thought to have taken only a few tens of thousands of years. In just 200 million years, possibly less, the Earth was essentially formed, though still molten and subject to constant bombardment from all the debris that remained floating about. 

At this point, about 4.5 billion years ago, an object the size of Mars crashed into Earth, blowing out enough material to form a companion sphere, the Moon. Within weeks, it is thought, the flung material had reassembled itself into a single clump, and within a year it had formed into the spherical rock that companions us yet. Most of the lunar material, it is thought, came from the Earth's crust, not its core, which is why the Moon has so little iron while we have a lot. 

.....

4 billion years later people began to wonder how it had all happened.