Smell (chemical environment) was probably the "original" sense, followed quickly by touch (slow macro pressure) and hearing (fast micro pressure). Pretty much every animal has those, even if they lack the brains to do much sophisticated with them.

Sight came way, way, way, way, way, way, way later. Encoding language in sounds is an even more recent innovation, in the grand scheme.

This may also be why we have such trouble assigning words to smells, and you can't write a poem to replace a hug, for instance. They're processed by entirely different, and far more primal, parts of the brain than language.

I never thought about it before but if someone had asked me I probably would have guessed the same - humans are probably biased to assume hearing must involve ears.

OTOH, detection of mechanical vibrations seems like the kind of adaptation to evolve early. Hearing is in some sense just a refinement of that, so at the very least the groundwork for it must be old.

Remarkable nature. Whenever my daily problems get on top of me, I like to spend a moment to think about the absurd but beautiful reality that we creatures exist and that we're hurtling through space. And now... that worms can hear... in a way similar enough to humans.