So how did God bring about the diversity of life we see on earth today? First he needed a place where life could survive—a planet that is just the right distance from the sun, and full of the right kinds of elements. God orchestrated this through physical processes that scientists have come to understand quite well. And many of these appear to have been fine-tuned so life could exist.
At the beginning of the universe, there were no galaxies or stars or planets, just hydrogen and helium atoms randomly distributed through space. But the gravity pulled big clumps of these atoms together to form stars. The strength of gravity had to be precisely tuned for that to happen. If it had been just a tiny bit stronger, it would have pulled all the matter in the universe back into one giant ball; if it had been just a tiny bit weaker, the atoms would have spread out so far from each other that stars could never have formed. As it is, God ensured that the strength of gravity is just right so that stars could form and provide the energy needed for life to exist.
So the first stars were composed almost entirely of hydrogen and helium atoms, but other natural forces besides gravity cause them to fuse into the other elements we need for life. For example, all the life we know of is based on carbon. To get one atom of carbon, you need three atoms of helium. Under normal circumstances, it is extremely rare for three helium atoms to fuse into a carbon atom. But inside a star the forces are so precisely balanced that there is lots of carbon produced from helium collisions. When the first stars ran out of fuel, they spewed their elements back into space. And gravity brought the atoms together to begin the process again. But this time, there were lots of other elements too that could gather into planets around a star; and at least one of those—our Earth—was positioned perfectly so that life could develop.
There are many other laws and constants in nature that had to be precisely tuned for the universe to support life. God could have brought all this about in an instant if he had wanted to. But the evidence we find today in the things he created points to the conclusion that he did it through these natural processes over long stretches of time.