Sand and stones dissipated heat quickly, and desert temperatures between day and night were at different extremes. In fact, the temperature difference between the noon and early morning could be in excess 30 degrees Celcius.
One could either roast under the scorching sun or freeze at the drastically falling temperature at night. Also, to avoid the many venomous snakes and insects that made the desert their home, Zhang Heng chose a relatively high terrain to start a fire. Besides, fire also prevented larger and more dangerous predators from approaching them.
