“Panspermia alleges that life exists and is distributed uniformly through the Universe in the form of amino acids, microbes, germs and spores. If life arose extraterrestrially, then our planet is not a closed system. The fossil evidence shows that life took root on Earth as soon as possible once the heavy bombardment period subsided, the planet cooled and water formed. Vulcanism and space debris made conditions inhospitable to life for the first half-a-billion years of planetary existence.
This “seed of life” can travel between worlds and arrive by natural means such as ballistic impact, meteorite and comet. Intergalactic space may be permeated with cosmic dust and microbes. Evidence shows they could survive the hard-core radiation and the near-absolute cold of deep space. Some researchers (Hoyle and Wickramasinghe, 2000) believe these “seeds” of life are raining down on us all the time, affirming our cosmic ancestry.”