We now know that the sun will eventually start to cool down, expand and explode. Mankind hopes that well before that it will escape from earth and colonize other planets so that the human race as it exists on earth can be preserved. This is easier said than done. Interplanetary travel from one habitable planet to another is a daunting task for the most advanced of civilizations and even if it did become possible one may find on arrival on another planet that the precise chemical composition of the new planet has made all available food toxic. The mineral compositions of planets vary.
Mankind need not despair. Nature has devised a better plan. In fact it has been in place ever since the universe has existed. When a star begins to cool down, most forms of life are frozen into extinction. However many bacteria, including the most useful ones have the ability to go into frozen hibernation and do so promptly on freezing up. Most significantly, these bacteria contain the genetic codes of all higher life forms on the planet as entrapped viruses and extra chromosomal elements.
When a star system dies and explodes, bits of its planets are ejected into the cosmos at varying trajectories. These bits of comets head for other star systems. On reaching another star they are pulled towards it by gravity. The warmth of that star begins a process that leads to disintegration of the comet into smaller bits. This phenomenon can be observed frequently in our galaxy. Some bits land on planets that are too cold and remain in frozen hibernation. Others land on planets without atmosphere or those that are too hot and die. Bits reach planets with a livable climate. Here with the availability of light and moisture, the bacteria wake up from their long hibernation and begin to multiply. If the planet already contains life, they join in bringing in new genetic codes. If the planet is toxic then the bacteria is able to make adjustments quickly to overcome the toxins. We see them doing it all the time with modern antibiotics. Incase the planet has no life, water and oxygen it does not matter. Bacteria know how to prepare that too. The cyno-bacteria are the first to wake up and with the help of light and carbon dioxide on the planet begin to produce oxygen. Methane-producing bacteria produce methane. The methane and any hydrogen on the planet then combine rapidly with oxygen producing more water and carbon dioxide. The process goes on until we end up with an atmosphere like that of earth. Plants and higher life forms then emerge by a process already described. Eventually humans reappear all adapted to a somewhat different environment of the new planet. With their ancient genetic memories, a process of recreation of civilization begins once more.
In this process, the comets are the spaceships of God and the little bacteria the workers that travel on these ship that create a habitat. Bits of comets that break off are like shuttle flights that take off from this gigantic spaceship. Comets travel from star system to star system. They also travel to other galaxies. It is easy to pick out the comets that have come from other star systems or even galaxies as compared to local asteroids etc. This is because in any star system there is a plane in which the local planets lie because of gravitational effects. Comets that come at a different angle are from other star systems. There are such gravitational planes of galaxies as well that can help identify comets of other galaxies.
Because of the cosmic sharing mechanism, similar life forms exist throughout the universe. However, it can be expected that a human from one planet will look quite different from that on another planet because of local influences i.e. planetary physical features are distinct on distinct planets. Since comet spaceships are flying around the galaxy on continuous basis, genetic codes from different planets arrive on any planet on several occasions. This leads to a situation where the code for the same species including humans arrives on earth from different planets on more than one occasion and this may result in the distinct features of different races