Nature not only provides us with a colorful visual feast but also brings us wonderful and shocking auditory enjoyment.

Various animals compete to show off their voices. Unexpectedly, the animal that won the title of "the loudest voice on earth" was not a hippopotamus, elephant, tiger, or lion, but the "heavyweight" singer from the ocean, the blue whale.

Sound waves travel much faster in water than in air: the speed in seawater is about 1,500 meters per second, while in air it is only 340 meters per second—more than four times faster.

You may not feel it when standing on the coast, but the water is rolling under the waves and the sound of orchestral music is endless.

Under the waves, the sea swallowed up the sun. Just 200 meters below sea level, photosynthesis is impossible. At 1,000 meters, the light stopped. This is the deep ocean—the largest, darkest habitat on Earth.

The deeper you go into the ocean, the less important the sunlight becomes, while the sound status becomes more prominent.

Cetaceans such as dolphins and whales all need to use sound to understand each other, navigate, and even rule a territory. It’s no surprise that cetaceans rely on sound far more than other species.

When the ancestors of dolphins and whales migrated from land to sea, their anatomy changed dramatically to adapt to their new environment: their eyes shrank, their forelimbs evolved into flippers, and their hind legs merged into fins. No longer needed to maintain body temperature, their body hair has disappeared, replaced by a thick shell of blubber that swells from fat, allowing whales to maintain a constant body temperature in the coldest waters in the world.

The hearing organs of dolphins and whales have evolved greatly to adapt to the underwater acoustic environment. Water is denser than air, so when sound waves enter the ears of cetaceans, there is almost no "acoustic impedance": that is, the sound waves pass through the heads of marine creatures in a straight line, rather than entering the ears with a certain refractive index like land animals.

After the sound waves reach the whale's skull, since their speed or power does not change, a kind of "sound wave interference" occurs between the ears, which causes some interference in their ability to locate the sound source.

To avoid this interference, cetaceans have evolved pockets of air in their ears. Their middle ear structures have moved from the inside of the skull to the outside: the tympanic membrane (ear drum) and ossicles (ear bones) are enclosed within a huge, spherical bony shell called the tympanic vesicle.

The combination of these factors, along with the unique organs that cetaceans have evolved, allows them to perceive and use sound in a way that is different from other animals on Earth. Humans' perception of sound waves ranges from 20 hertz (Hz) to 20,000 Hz, while a bottlenose dolphin can hear sounds at frequencies as high as 160,000 Hz - well beyond the range of dogs.

Bottlenose dolphins are susceptible to high-pitched tones that we can't hear: their radio frequencies are around 44,000 Hz. All creatures on earth use sound waves to some extent, but toothed whales are among the best high-pitched speakers in the animal kingdom.

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