I dunno about you but it seems I’ve been coating every place I’ve lived since I was about 12 years old. Particularly bathrooms, certainly when I was very young that was a common place. Bath tubs, shower stalls, even toilet seats!
Since the sperm can survive the harshest of environments, it can’t even be digested. There would be a thick coating of sperm over everything. Feet? Hundreds of feet? Oceans and lakes would just be swamps of sperm.
Unprotected sex? The environment is filled with live sperm. It will be in her blood stream. Her ovaries will produce fertilized eggs. Not to mention evolution will be going wild with hybridization, sperm from every species is everywhere.
I am having a hard time understanding how humans evolved in such an environment in the first place, but since we’re here we might as well get used to it.
What percentage of volume of ejaculate is sperm anyway? It can’t be much. Most of it is just semen, and that’s not invulnerable in the OP.
Remember, sperm/semen doesn’t just spring into existence out of nothing. The mass for it had to come from something. So oceans rising 100’s of feet would mean that there’s suddenly a lot more mass in the ocean, I guess it came from the continents? So did the continents all shrink too?
But yeah, birth control becomes absolutely necessary, all women are put on birth control by the age of 7 or 8 or so.
Luckily, STDs and such aren’t carried within the sperm themselves, but in the seminal fluid, so at least we don’t have to worry about that.
That would really, really mess up the whole story of how Jesus was conceived.
Me, I have never been so relieved to have an IUD in place. Frankly, I think gynecologists would be implanting them proactively well before a girl hits puberty.