I remember reading a sci-fi novel back in the mid 70s in which the Earth was threatened by some sort of geological or astronomical catastrophe - can't remember if it was a collision from another celestial body or super earthquake or such, but the Earth could be "split in two". About the only detail which stood out in my mind played upon my juvenile sensibilities about sex and sexuality. As disaster loomed, a couple somehow involved in an effort to preserve the human species were at some point dressed in transparent clothing (uniforms, survival suits, or something). At the time it seemed rather racy, in hindsight it might have been something thrown in entirely gratuitously by the author. Anyway, if I recall correctly, the story ends with this couple being among the few survivors left to repopulate the planet.
I have an uncertain recollection of a title something along the lines of "Worlds in Collision" or "When Worlds Collide", but Googling turns up either non-fiction or stories which don't seem to fit.
Can anyone identify the title/author of this story?