On our planet, the only place that humans have not conquered is the underwater world. Today's human beings have climbed Mount Everest, the highest place on earth, many times. After many times of space travel, the artificial probe has reached the outer space of the solar system. However, what the deepest part of the ocean looks like is still unclear. Because of the high cost of exploring the seabed, many problems are difficult to solve. However, according to the information currently available, the rewards of exploring the underwater world will be extremely rich, because in this dark world, the reserves of minerals, natural gas and oil are very rich. In addition, the exploration of the wonderful world under the sea is likely to change our traditional view on the origin and evolution of life on earth. In addition to these tangible benefits, there are some intangible but tangible satisfaction, which is the great pleasure of exploring the last edge of the earth. The ocean that has not been conquered by human beings so far accounts for 3/4 of the earth's surface, with a seawater volume of 654.38+0.4 billion cubic kilometers and an average depth of 3,700 meters. The intricate food web in the ocean breeds a wide variety of marine life, which is much more complicated than any ecosystem on land. From sulfur-eating microorganisms and bacteria living near the submarine crater to all kinds of deep-sea fish, their fluorescence can illuminate far away and attract many creatures to eat. In some places, there may even be a new species called "sea monster", including the 20-meter-long horseshoe crab. Scientific research tells us that in this underwater world, the potential economic value is immeasurable: the vortex ocean current with huge energy affects the weather in most parts of the world. If we can understand their formation mechanism and laws, we can predict the occurrence of climate disasters and avoid trillions of dollars in economic losses. There are also huge nickel, manganese, iron, cobalt and copper with commercial development value in the ocean; Bacteria, fish and plants in the deep sea may become the source of magical drugs to protect human health and longevity. It is estimated that in the next few decades, the benefits brought by the ocean will far exceed the benefits brought by human exploration of space at present. If people can freely and safely enter and leave the seabed, its economic benefits will be immediate. However, reaching the bottom of the sea is the same as reaching outer space. It is impossible for people to reach the bottom of the sea without special equipment. Common sense tells us that without the help of oxygen tanks, people can't dive below 3 meters for a long time-this is only one third of the average depth of the ocean! With the continuous diving into the water, the pressure is getting bigger and bigger. People's inner ear, lungs and some pores will feel pressure and feel pain. When the underwater temperature is low, it will quickly absorb the heat of the human body. It is difficult for people to stay in water below 3 meters for 2 ~ 3 minutes. For these reasons, contemporary deep-sea exploration has to wait for the development of two key technologies: deep-sea spherical submersible and deep-sea steel ball submersible tied with chains. People who can swim have been thinking about how to get oxygen underwater. It has been like this for thousands of years. In ancient Greece, divers got oxygen from bottles filled with gas, but in modern times, divers used compressed air to dive into human bodies. Usually people can dive to a depth of 30 meters. Even the most experienced people who use underwater breathing apparatus dare not venture to dive below 45 meters, because the increase of deep diving pressure and the pressure change in the process of floating to the surface lead to decompression sickness and even death. Using a sealed diving suit, you can only dive to a depth of 440 meters. The spherical submersible created a depth of 923 meters, but it was very difficult to operate. Later, a small deep-sea submarine was invented, but it can only be used for scientific research. The advanced deep-sea submarine is equipped with underwater camera, specimen collection basket and manipulator with human hand function. The practice of submersible gives a positive answer. The United States, France, Japan, Russia and other countries have developed deep-water submarines for different purposes and collected data samples of animals, plants, rocks and water samples in the depths of the ocean. This opened a new era of deep-sea exploration. People have gained a lot of information in the deep-sea world, which has changed some traditional views of biology, geology and marine geography. Scientists look at the changing law of wind and current with new eyes; El Nino in the Pacific Ocean is very harmful to commercially valuable fish stocks, and it can also induce strange changes in the climate on the earth. The instability of ocean circulation may lead to global climate change, or make the stable climate on the earth slowly disappear. Scientists also realize that the seabed at the bottom of the ocean is not flat. It is undulating and more complicated than our land topography, and its canyons can hold up the Himalayas. What's even more amazing is that there is a unique and global mountain range of 60,000 kilometers at the bottom of the sea. Like a giant snake, it winds through the Atlantic Ocean, the Pacific Ocean, the Indian Ocean and the Arctic Ocean. Scientists call this undersea mountain range "the mid-ocean ridge". By the end of 1970s, when geologists carefully studied the mountains in the middle of the ocean, they became more convinced of the tectonic plate theory. According to this theory, the earth's surface is not a single stone shell, but consists of several huge plate structures, the smallest of which is several thousand square kilometers, floating on the mantle. The uplift of the mid-ocean ridge may be the place where the crust first formed; The new plate structure may be caused by the internal force of the crust below the seabed before its formation. Rock samples collected from the mid-Atlantic ridge prove this. This is amazing evidence of the correctness of plate structure theory. The bottom of the sea has been flowing.