Life on a global biosphere basis is substantiated in the form of organics and organisms, and defined as the intermediate forms (briefly expressed as CH2
O) hovering between the reduced (CH4
, methane) and (CO2
, carbon dioxide) ends, different from the classical definition of life as a complex organization maintaining ordered structure and information. Both definitions consider sustenance of life meant as protection of life against chaos through an input of external energy. The CH2
O-life connection is maintained as long as the supply of H and O lasts, which is in turn are provided by the splitting of the water molecule H2
O. Water is split by electricity, as well-known from school-level experiments, and by solar radiation and geothermal heat on a global scale. In other words, the Sun’s radiation and the Earth’s heat as well as radioactivity split water to supply H and O for continued existence of life on the Earth. These photochemical, radiochemical and geothermal processes have influences on the evolution and current composition of the Earth’s atmosphere, compared with those of Venus and Mars, and influences on the planetary climatology. This view of life may be applicable to the “search-for-life in space” and to sustainability assessment of astrobiological habitats.