Page 73 - The Glory in the Heavens

energy given off by the Sun would result in the Earth's

surface being covered by layers of ice many metres

thick. Yet if the Sun's energy were to increase a little,

all living things would be scorched and die.
The speed the Earth spins at also helps keep the

temperature distribution in balance. The Earth makes

a complete rotation once every 24 hours. For this rea-

son, the alternating periods of daylight and darkness

are short. Because they are short, the temperature dif-

ferences between night and day are quite small.

The importance of this can be seen in the extreme

example of Mercury, where a day lasts longer than a
71
year and where the difference between day-time and
night-time temperatures is almost 1,000°C (1,800°F).

Geography also helps distribute heat equally

over the Earth. There is a difference of about 100°C

(212°F) between polar and equatorial regions of

Earth. If such a temperature difference were to exist

over a completely level area, the result would be wild

winds sweeping away everything in their path.

Instead, Earth is full of geographical barriers that

block the huge movements of air that such tempera-
ture differences would otherwise cause. Those barriers

are chains of mountains like the one that stretches