Someone once gave an imaginary metaphor: the sea water, which occupies the largest amount of the earth's surface, is contained in the ocean basin, the largest and deepest basin on the earth. After billions of years of evolution and development, there is now a total of about 1.33 billion cubic kilometers of water on the earth's surface, of which seawater accounts for about 97.3% of the absolute majority. If seawater is distributed evenly on the earth's surface, the water depth is about 2600 meters! If the height of the land and the depth of the ocean around the world are counted separately, we can find that the distribution between the two is not continuous: the land is mainly in areas with an altitude of 0 to 100 meters; while the ocean is mainly in water depth of 3,000 to 6,000 meters. The average ocean depth is approximately 3680 meters, and the average land altitude is approximately 800 meters. Why are there two different peaks?
It turns out that there are two different types of crust on the earth: oceanic crust and continental crust. The main component of the oceanic crust is basalt, with a density of approximately 2.9 g/cm^3; the main component of the continental crust is granite, with a density of approximately 2.7 g/cm^3. Beneath both lies a mantle of peridotite composition with a density of 3.3 g/cm^3. According to the principle of balanced compensation, the heavy crust sinks and the light crust rises, so there is a difference in depth between the continent and the ocean. Not only that, the heavy crust is thin and the light crust is thick. The average thickness of the oceanic crust is less than 10 kilometers, and the average thickness of the continental crust is 33 kilometers. Moreover, the higher the mountains on the ground, the deeper the "roots" below, and the thickness of the earth's crust on the Qinghai-Tibet Plateau exceeds 70 kilometers!
Trench is the deepest part of the ocean. This is because trenches are places where the earth's plates subduct, that is, where the earth's crust dissipates and penetrates downward into the mantle. The deepest Mariana Trench is located at the bottom of the Pacific Ocean northeast of the Philippines, near the Mariana Islands. This trench has a total length of 2550 kilometers, an average width of about 70 kilometers, and a water depth of more than 8000 meters in most areas. After detection, the deepest point of the trench is 11034 meters away from the sea surface, and it is also the deepest point on the earth. At the deepest part of the trench, the pressure is as high as 1100 atmospheres, just like the pressure generated by a car parked on a dime coin! Even so, scientists have successfully descended to the bottom of the Mariana Trench in deep-sea submersible many times for scientific investigations. In such a deep sea, in eternal darkness, and under such great pressure, scientists have even discovered flounder and red shrimp swimming freely!