Considering mankind's usual suspicious function, I believe that it takes quite a bit of arrogance (Exponential) to think that in such a vast universe , our planet is the only planet with eukaryotic life forms. Many theories exist as to prove or disprove, but the arrogant mind always seems to prevail. Our earth, in all of its glory, is truly a speck of dust in the Milky way galaxy, much less the grander universe in which we live. Glacial periods are needed to keep species in check wherein extremophiles will most certainly survive. Suppose if, just if, our earth had began as a molten mass of Iron freely floating in space. what if it were to have impact with a comet of grand scale. Comets being formed from gasses, dust, minerals, and ice. The hot "quench" would form an atmosphere, leaving oceans of water behind under the new atmosphere. These oceans would probably contain many different particles of the original comet (which was ice based), and possibly traces of organic carbons. Ice is a very important mode of transport in our universe and our world, making sure that the seeds of life can find the best places to sprout.