Even in the coldest places on earth there is life, and favorable microclimates make it possible. For example, in the Antarctic mountains, where the air never gets above freezing, a north-facing rock surface on a sunny day can get much warmer. Although temperatures right on the rock surface can rise above freezing in the direct sunlight, the very dry air and rapid fluctuations in temperature prevent any form of life from growing there. Over just a few minutes, the temperature can rise above freezing and dip back down below, and this sort of instability seems to be too much for even the hardiest organisms to cope with. However, conditions are warmer and more stable a few millimeters down between the grains of a sandstone rock. The grains are transparent quartz, which allows sunlight in but provides insulation from the chilling air outside. Temperatures in the tiny gaps between these quartz grains can get much warmer than the surrounding air: to around 10°C, which is some 20°C warmer than the air outside ever gets. It is within these miniature greenhouses that specialized "endolithic" (meaning "within-rock") lichens live, photosynthesizing and growing during the few weeks each year that are warm enough, and perhaps living for centuries in a mainly dormant form.
In another of the earth's most extreme environments, lichens can also survive within rocks due to the right microclimates. Death Valley in California holds the record as the hottest place on earth. Sandstone rock faces baked by the sun and parched by lack of rain seem an unlikely place to find life, and indeed the rock surface itself has nothing growing on it. Yet, a few millimeters deep inside the rock temperature extremes are lessened and there is moisture that trickled in between the rock grains when it last rained. Endolithic lichens survive here, harvesting sunlight that reaches through the quartz grains of the rock.
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