Pour yourself a hot cup of water, and let it sit for a while, you will see short-lived microscopic bubbles forming on the surface.
You may need lighting near parallel to the water surface to see the bubbles.
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Clusters of water molecules escaping from the liquid to gas phase. Molecules closer to the surface are closer to vapor state because they have less pressure exerted on them.
There are two things happening. First, the solubility of gasses in liquids decreases as a function of temperature, so some of the bubbles are things like nitrogen leaving the aqueous phase. Second, some of the water is turning from liquid to vapor. The surface tension of the water is keeping it from floating off into the air
It’s not quite true that all H2O is liquid until 212F. There always some water turning to vapor, which is why a spill evaporates over time. There’s even some small amount of vapor above ice? In fact, there’s a teeny, tiny amount of vapor being released by everything… even an iron bar has some iron vapor above it.
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