Sound: 13.7 billion years ago
Sound has its origin far back in time, not long after the disappointingly silent Big Bang. In fact, sound waves formed as soon as there was a medium for them, which was 300,000 years after the beginning of everything, and thirteen billion years before there was anyone to listen.
The primordial sound was of a very low frequency, but powerful and omnipresent, and it formed when the plasma of the newborn universe arranged itself in pseudo-regular patterns through space. Galaxies eventually formed in the denser regions, including the progenitor of the world we live on and the sun we orbit.
Moving on a few billion years to the first days of Earth (about4.6 billion years ago), there were sounds aplenty, passing through the solid planet’s crust and its subsurface liquid areas, and bouncing and bending through its atmosphere. Eventually, the hot land cooled, rains fell, and oceans formed—oceans full of sound. So, the environment in which the first living things evolved was an acoustically rich one, which profoundly affected the forms, habits, and destinies of those creatures.
Hearing: 500 million years ago
For us, there is a clear distinction between hearing and feeling, but it’s a very different matter for undersea creatures: sounds pass as easily through their bodies as vibrations do through ours, and, in fish, are detected by structures called neuromats, which are distributed over their body surface (fish have several other hearing structures too).
Neuromats contain hair cells similar to those in our ears and provide their owner with information about the strengths and directions of local sounds. They evolved perhaps 500 million years ago. To detect airborne sound, eardrums and cochleae are essential, and hence evolved once amphibians began to colonize the land, around 400 million years ago. Communication was probably the main spur to the evolution of hearing, since sounds have overwhelming advantages over visual signals: while the ability to make lights and change colours exists in some marine organisms, putting on a light show is far more challenging and narrower in range than making noise. Noises are made easily—as easily as breathing. In humans, breath-made sounds (precisely controlled by our big brains) gave us the power of speech.