The speaker told us plenty of interest things about the deep sea. One hundred years ago, human beings believed that there was absolutely no life in the deep ocean. The reason was very simple and reasonable: Sunlight could only penetrate 200 meters seawater and hence the deep ocean was completely dark. Therefore, photosynthesis of plants stopped and animals had no food.
However, the previous assumptions proved to be wrong. With the development of submarine boat, humans can even reach the ocean floor of ten thousand meters deep. We are totally astonished to find a vigorous world under the sea. As you can see from the above picture, there is a submarine chimney, which is hot lava. There is full of lives around it. The submarine chimney provides heat and inorganic elements to germs, which are the food of other animals. Human beings know nothing about these lives.
There are plenty of secretes in the deep ocean waiting for us to explore.