Toutes les eaux ne sont pas habitables

Terrestrial life is known to require liquid water, but not all
terrestrial water is inhabited. Thus, liquid water is a necessary, but
not sufficient, condition for life. To quantify the terrestrial limits
on the habitability of water and help identify the factors that make
some terrestrial water uninhabited, we present empirical
pressure-temperature (P-T) phase diagrams of water, Earth, and
terrestrial life. Eighty-eight percent of the volume of Earth where
liquid water exists is not known to host life. This potentially
uninhabited terrestrial liquid water includes (i) hot and deep regions
of Earth where some combination of high temperature (T>122°C)
and restrictions on pore space, nutrients, and energy is the limiting
factor and (ii) cold and near-surface regions of Earth, such as brine
inclusions and thin films in ice and permafrost (depths less than 1km), where low temperatures (T<−40°C), low water activity (a_w<0.6),
or both are the limiting factors. If the known limits of terrestrial
life do not change significantly, these limits represent important
constraints on our biosphere and, potentially, on others, since 4
billion years of evolution have not allowed life to adapt to a large
fraction of the volume of Earth where liquid water exists. Key Words:
Biosphere—Limits of life—Extremophiles—Water. Astrobiology 10, 349–361.