Another goal is to improve the submersibles' capacities to travel greater distances and stay longer underwater. Currently, Fendouzhe can stay six hours in the Mariana Trench, Gao says.

Besides, Chinese scientists hope to create larger cabins so as to carry five pilots for comprehensive scientific voyages with a better living environment.

While writing the book, Gao was impressed by the "black chimneys" found on the sea bed. They are basically mini volcanoes, superheating the water as they discharge minerals, metals and gases — at temperatures ranging between 200 C and 400 C — into the bitterly cold deep ocean from below the seafloor. They are also home to many living organisms.

"It amazed me that living creatures exist in such hot water," he says. "It's like another life system. Maybe it can provide another theory about where human beings come from."

He was also deeply impressed by the courage of Wang Pinxian, an academician of the Chinese Academy of Sciences. In 2018, 82-year-old Wang took the Jiaolong submersible and dived to the depth of 1,400 meters in the South China Sea three times within nine days and made many important scientific discoveries.

"There are many younger scientists who would not dare to make such a dive," Gao says.

For him, to explore the ocean is vitally important for the survival and development of human beings.

"The resources on land are limited. Humans have to explore the ocean, which accounts for 71 percent of the surface of our planet, and make use of it — perhaps in the future, even find a way to live in it, due to the explosive growth in the global population," he says.