Early Life
The Ancient World
© Giles Laurent, gileslaurent.com, License CC BY-SA, CC BY-SA 4.0
Now we have the answer to the age-old question: if quantum compression waves ripple through the plasma of the primordial universe and there’s nobody there to hear it, does it make a sound?
The answer is yes, if by 'sound' all we mean is the waves themselves. On the other hand, it might match up better with the commonsense meaning of the word to say those waves are not ‘sound,’ but only what sound is made of. For most people, ‘sound’ means the subjective, qualitative experience of hearing. The question is not what a sound is physically made of, but what it sounds like to the listener.
Hearing, is (cosmologically speaking) a rather new phenomenon. After the Big Bang, the universe expanded rapidly, forming nebulas, stars, and galaxies. After about nine billion years, a huge cloud of hydrogen gas compressed under the force of its own gravity and exploded, starting a nuclear fusion reaction that we call the Sun. Swirling clouds of gases and heavier elements orbiting the Sun began to cluster together, and something like four and a half billion years ago, the forces of gravity pulled those together to form the planets, including the Earth.
This first phase in our planet’s history was called the Hadean Eon. The young earth was not only volatile and highly volcanic, but open to impacts from meteorites and even other planets, including the impact scientists believe formed the Moon. It would have been very loud, if there had been anyone there to shove their ears against the planet’s surface to hear it. Soon, our planet’s gravity captured enough gases to form the atmosphere. Sound waves could now travel through the air. The planet’s temperature stabilized, turning out just right for liquid water to rain down and form the oceans.
At that point, something amazing, even miraculous, happened. In those newly formed oceans, life emerged. Tiny little creatures suddenly began responding and adapting to their environment, absorbing and metabolizing energy from their surroundings, using that energy to nourish and replicate themselves. Nobody knows how it happened. The chemical conditions of the early world may have been able to produce amino acids, proteins, and nucleic acids, which are the building blocks of life… but not life. We have only ever actually observed life coming from other life. There’s no record of how it got going. But it did. The laws of chemistry literally changed. Earth became a very special place.
These little creatures were minute, single-celled organisms. They couldn’t see and they certainly couldn’t hear, but they were undoubtedly alive, and they had ways of reacting to the world around them. Their time – about 4 billion years ago – is called the Archaean Eon.
Amir Ali Iranshahi 3, CC0, via Wikimedia Commons
Eventually, a distinction emerged between life-forms that used photosynthesis to draw energy from the Sun, and those that got their energy by preying on other life-forms. This was called the Proterozoic Era, and it’s when life began to separate into animals and plants. This went on for a long time, until about 540 million years ago, when we have the Cambrian Explosion. After millions of years of single-celled Proterozoic creatures, we suddenly find in the fossil record an effusion of multicellular organisms, complex animal life-forms with unique body types and all sorts of different organs and systems working together. After 200 million years we have all the major animal phyla we recognize today: mollusks, sponges, worms, insects, starfish, vertebrates, and quite a few others. The Cambrian Explosion marks the start of the Paleozoic (“Ancient Life”) Era.
The first vertebrates to appear were fish. Like modern fish, Paleozoic fish could detect sound waves traveling through the ancient oceans. In fact, sound waves travel farther through water than air, so this was probably a very important way for these animals to gain information about their environment. Fish have ears inside their heads, and modern research has shown that most fish can hear frequencies from below the range of human hearing up to about 1000 Hz. While the ability of fish to detect and respond to sound waves in the water is clear, one thing to keep in mind is that fish are really stupid, and it’s not at all clear if their experience of hearing is anything analogous to ours, or if what’s going on in the mind of a fish is even what we would call experience at all.
It took another 200 million years for the next big development, where the fossil record shows that Paleozoic life had crawled out of the ocean and made a home on the land, beginning the “Middle Life” or Mesozoic Era. This marks the appearance of the first creatures with a tympanic membrane, or eardrum. That’s important, because when it comes down to it, we still hear the same way fish do. The part of your body that actually allows you to hear is your inner ear. Just like a fish, it’s inside your head and it detects sound waves moving through fluid. What an eardrum does is take sound waves from the air passing through your outer ear and use those to shake a tiny membrane attached to the stapes, or stirrup, which is the smallest bone in your body. Those vibrations then pass through the cochlear fluid in your head to the inner ear, where you can hear them.
Not everyone keeps their tympanic membrane in the same place. The ears of crickets can be found on the tibia bones of their forelegs. The tympanic membranes of amphibians and some reptiles are inside their heads, like fish. Other animals, like birds and probably dinosaurs, have very small, almost unnoticeable external ears. In whatever form, this development was present in animals throughout the Mesozoic Era, which is divided into the Triassic, Jurassic, and Cretaceous Periods, and of course is the age of the dinosaurs. Now there is no way to know what was going on in the inner consciousness of a triceratops any more than a fish, or a dog or cat or anything other than a human being for that matter, but dinosaurs were just as advanced as the animals of our time, and there’s no reason to think their experience of hearing wasn’t at least similar to ours. They may not have spent any time reflecting on the beauty of what they heard, but it probably hit them more or less the same way.
Julian Fong, CC BY-SA 2.0
Dinosaurs and other Mesozoic animals could not only hear sounds, but they could make them. These days, most peoples’ imagination of dinosaur sounds is a product of the 1993 Steven Spielberg film Jurassic Park. To create that distinctive call, the movie’s sound designers combined the vocalizations of an elephant, a tiger, and an alligator. The resulting roar is certainly terrifying, but not especially accurate. Only one of those animals - the alligator - is remotely related to the dinosaurs, and those lineages diverged in the early Triassic Period, 183 million years before the first Tyrannosaurus appeared. We might get a better idea of what the T-rex sounded like by listening to animals most scientists agree are directly descended from dinosaurs - birds.
An animal like a sandhill crane, which you can see and hear across the southeastern United States, still bears an uncanny family resemblance to Mesozoic theropods. However, a big sandhill crane weighs ten pounds, compared to a fully grown T-rex, which was closer to 15,000 pounds. Its much larger skull would have produced lower pitched frequencies. In 2018, scientists at the University of Texas discovered that the inner ear of a Tyrannosaurus would have been particularly sensitive to low frequency sounds like the ones we just heard. This makes sense, anyway: larger animals make lower sounds, and T-rexes weren’t out there hunting mice, they were listening for hadrosaurs and faraway herds of Triceratops. Adjusted for the body size of a T-rex, there is something ominous in those sounds that taps into a deep, primal fear we still have.
In August 1995, paleontologists digging for fossils in New Mexico discovered the almost complete skull of a Parasaurolophus. After running CT scans and computer models of the skull, researchers at Sandia National Laboratories and the New Mexico Museum of Natural History and Science were able to reproduce a range of sounds the animal would have been able to make. Those low frequency sounds are just what the Tyrannosaurus was listening for.
The Mesozoic Era ended in a flash 65 million years ago when an iridium-laden asteroid the size of Washington, D.C. slammed into the Yucatan Peninsula. The effects of this impact wiped out three-quarters of the life on Earth, and marked the beginning of the Cenozoic Era. Ice ages came and went as small, rodent-like mammals spread across the planet, and we start to see all the variety of modern mammalia: everything from tiny field mice and tree-dwelling marmosets to monstrous wooly mammoths and colossal leviathans. Hearing was very much a part of these creatures’ world. Mammals have the best-developed ears of any lifeforms, and they took in the sounds with the sights. Some of them, like Pseudaelurus, the ancestor of modern cats, used their hearing to hunt; others, like Cetotherium, a now-extinct whale, followed their ears to navigate the open seas. Still others could do both at the same time.
Of course, there is more to music than just hearing, and it would be millions more years before one special genus of mammal, and one noteworthy species in particular, would begin to fill the air with music.