The Cross of Freedom

Gravity had to begin having an effect on the universe between the time atomic nuclei could be formed and the time electrons could bind in orbit around those nuclei or the universe as we know it would not exist.  This is because the material density of the universe after the earlier event would have been too low for heavy element formation to occur.  Had the second event occurred without the benefit of gravity, there would not be enough heavy elements to build anything.

Gravity is the weakest of the forces of matter, yet is effective across vast distances.  The universe at this point was still something like a large cloud made up of gasses of hydrogen and helium.  It still had no form.  Gravity started to pull these gasses into clusters, which formed galaxies.  Within each galaxy, clouds of gas and tiny particles of minerals contracted to form individual systems.  One of these systems is our solar system.

As these star systems contracted, their spin increased.  Centrifugal force flattened the clouds into disks.  All the matter in these star systems did not get pushed to the outside edges because gravity had pulled, and continued to pull, much of the matter to the center of the system.  At the core of the system, pressures increased.  The nuclei of hydrogen and helium were squeezed together more and more tightly until, once the pressure was intense enough, nuclear fusion kicked in and stars were ignited and began to light the sky.  It's the fusion inside of stars that still produces all the elements present in our universe other than hydrogen and helium.  These elements are ejected from the star after all the hydrogen and helium within the star have been exhausted.  At this point, without the energy release to support them, the outer layers of the star collapse.  This causes the core to release a burst of energy as a massive shock wave.  The outer layers of the star, where the heavier elements are concentrated, are shot into space and these elements can then be used to form other star systems.

Within a star system, new clusters are formed from the matter that doesn't get pulled to the center to form the star.  These clusters grow to become planets.  Ices and frozen gasses on the surface of the solid particles that are clustering together become part of the substance of the forming planet.

By the time the planets of our solar system started to form, there would have already been a temperature gradient in our solar system.  This might explain why the planets closer to the sun consist mostly of rocky minerals and the planets farther out consist mostly of gases.

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