What sea does not exist on earth

Deep sea

Undiscovered depths

The term "deep sea" is used from a depth of around 800 meters. But it goes much further down: The actual sea floor, the so-called deep sea table, extends at a depth between 3000 and 5500 meters. The average is around 4000 meters.

Like the continents, the seabed is not flat and level, but traversed by ditches and large mountains. The deepest point on earth is the Mariana Trench, east of the island of Guam on the edge of the Pacific. It is 11,034 meters below sea level.

But there are not only trenches, a gigantic mountain range piles up under water and forms the mid-ocean ridge. It is over 70,000 kilometers long and runs through the entire Atlantic and from the southern tip of India past the Antarctic to Central America.

Deep sea research

Although people have been on the seas since ancient times, for a long time they had no idea what was hidden below sea level. It was believed that the sea was infinitely deep and that life was no longer possible from a certain depth.

An expedition by the British research vessel "Challenger" marks the beginning of scientific exploration of the oceans. The research ship cruised all the world's oceans from 1872 to 1876, took water samples, explored the seabed and discovered over 4,000 new animal species. And at least since the record dive of the "Trieste" in 1960, when researchers found a flatfish at a depth of almost 11,000 meters, it has been clear that there is still life even in the deepest depths.

Life in the deep sea

Life is everywhere in the sea: close to the surface, on the continental slopes and on the sea floor. The seas represent 90 percent of the living space on earth. And they are inhabited by strange and partly unknown beings. Ranging from bacteria and plankton to shrimps, crabs and crustaceans to gigantic octopuses, over ten million species of marine life are suspected.

The deep sea places special demands on its inhabitants: there it is pitch dark, ice cold, and the water exerts enormous pressure. Since no sunlight penetrates down, photosynthesis is not possible. There is practically no plant growth below 180 meters.

The animals have no choice but to eat the remains of dead plants and animals that slowly sink to the bottom. Or they will eat each other. All animals have one thing in common: Searching for food down there is very tedious.

Residents have developed special survival techniques

It is noticeable that most deep-sea fish do not grow very large - they measure no more than 30 centimeters. Apparently they cannot find enough food to keep growing. Many have almost transparent bodies or are completely black in order to better protect themselves from their enemies.

The eyes are either extremely large in order to catch the faint remnants of the light that still penetrates into the twilight zone, or they are missing entirely.

The animals then have other sensitive organs of perception with which they can track down their possible victims, for example through their smells or the vibrations they cause. Some deep-sea fish can send out light signals with the help of bacteria. This helps in communication with conspecifics and attracts prey - but also predators.

The scarce food supply makes people inventive. There are deep-sea fish with extremely stretchy stomachs and fold-out jaws. This allows them to catch prey that is larger than themselves, and thus provide for the time until the next catch.

Such properties often give the fish an almost grotesque appearance: the pelican eel (Eurypharynx pelecanoides), for example, has a mouth that is as wide as a quarter of its body length. Schlinger (Saccopharynx lavenbergi) are more like a vacuum cleaner bag.

The teeth usually look particularly terrifying: They are often extremely long and very sharp. The black dragonfish even has teeth so long that it cannot close its mouth. Such weapons are probably necessary in order to be able to effectively catch any prey, no matter how small, that swims by somewhere.

Black smokers

In 1977 researchers who were on the submersible "Alvin" near the Galapagos Islands made a sensational discovery: They found submarine thermal springs at a depth of more than 2000 meters. Hot magma, which is here very close to the sea floor, heats the sea water, which penetrates into the sea floor in other places.

Minerals from the earth's crust and sulfur compounds dissolve in the hot water and are emitted as black clouds of smoke from the chimneys. The sources are therefore called "black smokers". What is special about this discovery: around these chimneys with their toxic emissions of up to 300 degrees Celsius, entire communities of life consisting of bacteria, worms, crustaceans and other organisms have formed.

Giant tube worms are some of the most amazing creatures there. They cover the ground right at the edge of the chimneys and live inside shell-like tubes. The scientists were completely amazed: These worms have neither a mouth nor an intestine, an anus or a stomach. In theory, you cannot feed yourself at all. But their inside is lined with special bacteria. These bacteria live on the sulphurous water and convert it into nutrients, on which the worms in turn live.

The hemoglobin from the worms' blood, in turn, helps the bacteria break down the sulfur compounds in the water. This creates a complete food cycle: crustaceans, mussels, snails, spider crabs, jellyfish and sea anemones live directly or indirectly from the sulfur-consuming bacteria that can survive the extremely high temperatures.

Scientists now suspect that life could have started in the deep sea. One thing is certain: Just as entire communities of life around bacteria have formed in the "black smokers", so probably all life on earth began once.

Perhaps in this way life could also arise on other planets, for example on Jupiter's moon Europa. In this way, deep-sea research helps to gain knowledge about completely different habitats.