Capitalize Earth (d’uh!), ’cause it’s the proper name of a planet. (Yes, I know you’ve seen it uncapitalized in some published books. You’ve also seen comma splices, run-on sentences, and maybe even de facto used as if it meant matter-of-fact, but that doesn’t make any of those correct.)
Also, use end punctuation at the end of a sentence. In this case, because the sentence is declarative rather than interrogatory or exclamatory, use a period. (Most people learn this sometime around, I dunno, first grade or something. At least they used to. I’ve been out of education for a while, so I have no idea what is being taught to kids these days. If more English teachers were really doing their jobs, though, I wouldn’t have a current job, would I? And then I could retire, live on a beach and walk around naked if I want to… Um. Sorry. Somehow, a quote from a Muppets movie spliced in my brain with a scene at the end of a sci-fi novel, and I ended up unintentionally comparing myself to someone I generally try not to compare myself to. Please don’t ever tell my twin I did this, okay?)
You can delete up because anything that starts at the core and arrives at the surface is obviously moving up.
The creatures living in the Earth’s core finally come to the surface.
And now… the science part.
The pressure difference between Earth’s sea level and, say, the near-total vacuum of outer space is nothing compared to the difference between Earth’s core and its surface. Are you aware that part of the problem with trying to catch fish from the ocean trenches and bring ’em up for aquarium displays or study or whatever is that they pop when brought into our relatively oh-so-low atmospheric pressure? Now consider how much worse it would be for anything accustomed to living in the planet’s core, where the pressure is even higher than in the ocean trenches…
I’m not saying there’s not a cool story idea in this prompt, but I’d demand that the complications be addressed in the story.