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That's all pretty much correct.
We could produce more water on earth, by combining hydrogen and oxygen from other sources, but it's still a finite amount (even if incredibly huge).
But without extracting Hydrogen and Oxygen from other sources, the water we have on the planet mostly just gets recycled.
And it obviously wasn't all dinosaur pee, because most of the parts that make up pee (the urea) would settle elsewhere in the sea/rivers/land. The water eventually becomes pure water, as normal.
On the note of fusion, for those that don't know, that is basically recreating the internal process of the sun.
We combine atomic particles together (or atoms) to create new atoms. Unlike a chemical reaction, we end up with a new atom of a different element.
So, in a reaction of singular Hydrogen Molecules, they react and bind together to form H
2.
In nucler fusion of Hydrogen molecules (which consist of 1 Proton each), we squish them together to produce an atom with 2 Protons (but one would change into a neutron). We get 1 Helium (He) atom out of this.
Fusion produces lots and lots of energy when done, which is the reason behind the Sun's heat and light.
