As the universe continued to expand and cool after the Big Bang, atoms formed large clouds of gas, which are known as .

In the first moments after the Big Bang, the universe was extremely hot and dense.  As the universe continued to expand and cool, things began to happen more slowly.  for electrons to be trapped in orbits around nuclei, forming the first atoms.  formed from clouds of gas around 150–200 million years after the Big Bang.

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a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).