**2. Earth is a cold planet**

From a biological perspective, Earth is a cold planet. Most of the Earth's surface is covered by oceans where temperatures are below 5°C [9], and 80% of the terrestrial biosphere is permanently frozen [10]. Some examples of these cold environments are upper atmosphere, benthic marine zones, polar deserts (**Figure 1(A)**), glaciers (**Figure 1(B)**), subglacial lakes, and icy seas (**Figure 1(C), (D)**) [11].

Snow and ice cover over 108 km2 of the Earth's surface. Snow in winter can cover up to 12% of the Earth's surface [12], and approximately 10% of the planet's land surface is covered by glacial ice in the form of ice caps, ice sheets, or glaciers, accumulating 75% of the world's fresh water [13]. Mean temperatures observed in snow and ice environments can be highly variable at different depths, sites, or seasons. For example, surfaces exposed to wind are influenced by air temperature. Temperature can range from −50 to −70°C during the winter in the Arctic and Antarctic, respectively, to 0°C in summer [14].
