About every 250 million yeras, have read, a Delta ray goes through the Milky Way Galaxy. It would wipe out any life form, based on carbon, like ours.

We survive because while caught within the gravitational pull of the Milky Way, our star system exists about two thirds down and midway between to of the spiral arms. Thus so far it has passed us by.

Though nothing stays the same, so next time, who knows.