What is this?!

My house was built in 1917, and I’ve had it about 2 years now. I finally got fed up with the ugly gray carpets and impulsively (and maybe stupidly) decided to start tearing that junk up. Well, unsurprisingly, there’s more junk underneath. What the fack am I looking at??!

I started at the top of the stairs and was getting excited because the wood underneath seemed decent. Well I reacted too soon, because when I get to the bottom and the carpet comes up, there’s this stick and peel linoleum fake wood crap on top of what I think is the og wood flooring? But there’s this gooey black stuff. Is the wood old and rotted? Is this tar? Mold? Can I save this? I’m scared 😭