Mountains are formed where the earthâ
€™s plates collide. They make up a fifth
of the planetâ€™s surface, but account
for only a tenth of the population. They
appear on all continents as well as under
Even as mountains are rising as a result
of volcanic action or the buckling of the
earthâ€™s crust, they are being worn
away by wind, rain, ice and snow. The
Appalacians are being eroded faster than
theyâ€™re being built, while the
Himalayas are in stasis. Theyâ€™re
being built up and worn down at the
With over 71% of the planet's surface covered
by them, oceans are the largest habitat. Oceans
regulate earth's weather. They support the
greatest variety of life on earth, and they absorb
carbon dioxide--an essential function for the
preservation of life.
Much of the deep ocean has yet to be explored.
Forests are of two basic types--coniferous and
Coniferous trees have small, needle-like leaves
that stay green all year round. The northern
coniferous forests or taiga cover Canada,
Scandinavia, Russia and Mongolia--places where
the summers are short and the winters long and
Deciduous trees have broad leaves to absorb
sunlight. Those in colder areas shed their leaves
Jungles, or tropical rainforests,
are complex environoments filled
with life. Despite the fact that
they cover only a few percent of
the planet, they are the most
diverse ecosystems on earth.
Jungles around the globe are
being destroyed at an alarming
rate, endangering potential stores
of medicines and areas capable
of absorbing vast quantities of
carbon dioxide, reducing global
The distinguishing characteristic
of deserts is a lack of water.
Though some deserts are hot,
others are cold, but because
they are dry, they are open,
treeless and deserted.
A desert can be defined as
anyplace where rain or snow fall
more slowly than things dry up.
Ice covers an increasingly
smaller portion of the globe,
mostly near the poles.
The poles are frozen because
the planet is spherical and the
sun is low in the sky. That
makes shadows long and
spread over larger areas.
The poles have the greatest
range of daylight hours
throughout the year. The sun
never sets in midsummer and
never rises in midwinter.