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Language:English 英文
【Maintaining Energy Balance - Part 2: Earth and Life 维持能量的平衡下编-地球生命编】
the first ray of life. As the poet T.S. Eliot wrote: "What we call the beginning is often the end, and to make an end is to make a beginning."
In its early days, Earth received a gift from the universe: water (H₂O). The water system is a direct manifestation of energy balance: the breaking and re-forming of hydrogen bonds stores and releases heat; when liquid water cools to 0°C, it releases latent heat and forms ice crystal structures. With changes in thermal energy, ice (solid) absorbs heat to overcome hydrogen bonds and becomes liquid water; liquid water at 100°C absorbs 2258 kJ/kg (540 cal/g) of latent heat to vaporize, and water vapor carries this energy into the atmosphere. The three phases of water change according to energy variations to maintain their corresponding stable structures. When water vapor cools and condenses, it releases an equal amount of heat, driving convection and precipitation. Among these, the direct conversion of ice to water vapor requires absorbing 680 cal/g of energy, common in permafrost regions or polar ice sheet surfaces. When water vapor directly freezes into ice crystals (such as frost formation), it releases heat. In ice, water molecules form an ordered structure through hydrogen bonds, storing potential energy. Melting requires breaking hydrogen bonds and absorbing heat (latent heat); in water vapor, intermolecular forces are weak, and potential energy is stored in molecular kinetic energy. Water vapor acts as an "energy carrier," transporting solar energy absorbed by the ocean to land in the form of latent heat. About 30% of the global solar radiation is redistributed through the water cycle each year. The energy balance of the water system results from the dynamic coupling of phase-change latent heat, sensible heat exchange, and energy storage.
It is precisely the characteristics of the water system, combined with Earth's suitable temperature and the formation of the atmosphere, that provided the basis for the birth of life on Earth later. The presence of liquid water and water vapor as an "energy carrier" injected power into the development of civilization. "Stealing in with the wind by night, moistening things finely and silently" — after the emergence of humans, humans learned to harness the energy of the water cycle. Hydropower uses the energy of the water cycle, and nuclear fission power also uses water as a working medium to transfer nuclear energy. As Laozi said: "The highest good is like water; water benefits all things without contending." The balance of the water system is both a victory of physical laws and a gift of natural wisdom. Water is the "blue blood" that the universe gave to Earth; its three-phase changes weave a web of energy, nurture life, and nourish civilization. From deep-sea hydrothermal
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