The Earth's restless climate
Climate is always changing. The fluctuations of weather and climate take place on all time-scales, from the gusts and lulls of the wind, which occur within a fraction of a minute, to the shifts of regime over hundreds of millions of years associated with continental drift and wandering of the poles. Fortunately, however, for the development of life on the Earth and in particular for the evolution of contemporary life forms, the range of the temperature changes has been limited. Since the first appearance of life, there have presumably always been regions of the Earth where the air and water temperature remained generally between 20 deg and 30 degC (70 deg and 86 degF) and extensive regions where the limits of 0 deg and about 35 degC (32 deg and about 95 degF) were never far exceeded nor for more than a few hours at a time. This limited range bears witness that the sun must have been a reasonably constant star and the Earth a planet hospitable to the survival and spread of life. Nevertheless, the changes in the Earth's climate that have occurred have brought innumerable local and regional disasters and have repeatedly challenged the tolerance and adaptability of human and all other living entities.