Some deserts can be visited but not lived in. Some deserts are so inhospitable that life as we know it cannot survive in them at all.

In terms of rainfall, areas that receive less than ten inches of rain a year are considered to be deserts.

Some deserts receive only three or four inches of rain a year. A few places do not receive any rain at all.

When we think about deserts, we think about limiting factors.

on earth, liquid water is necessary for life. Some life forms survive periods when water is not available by becoming spores or seeds, or by becoming dormant (hibernation or estivation). Some plants can survive for many years as seeds. Insects and unicellular life forms can also wait out drought. Sooner or later, however, liquid water is necessary. Survival is essential, but it is not all of life. Without growth and reproduction, life is on hold, not progressing.

Salinity can also interfere with an organism's use of water. Fresh water fish cannot live in the ocean, and land pla

When we think of deserts, we often think of hot deserts with sand dunes. While it is true that some parts of deserts have dunes, desert landscapes vary widely. This picture shows a part of Monument Valley, which is an arid area. You can see sand in the foreground, but behind the sand there are some desert plants: probably rabbit brush. Notice that these plants are not close to each other -- there is not enough moisture in the soil to support more plants. However, there is something here for animals to eat. There are probably some little rodents in this desert -- mice or kangaroo rats, and some lizards. There will be a few snakes to eat the lizards and rodents. There will be insects, too. During the summer many of the animals will seek shelter from the heat by hiding in burrows underground. They will come out at night to hunt for food.

Deserts are described as areas that get an average of less than ten inches of rain a year. In the summer, temperatures may soar to over 120 degrees during the days, but will drop as soon as the sun sets. Winters may be cold. The dry desert air and clear skies do not hold onto the heat at night. The heat just radiates out into space.

Some plants are annuals. Their seeds wait in the ground for years until there is a rainy winter: then they sprout rapidly and grow as fast as they can. They race the sun to make seeds before the water evaporates and the heat dries them up. Some of these plants are so tiny that the whole plant could be hidden under a dime. Others spread colorful blossoms over the sand and rocks for a few brief days.

An interesting desert "extra" is the oasis, a place where springs of water flow to the surface, providing an environment where palm trees and shrubs may grow. Though rare, oases gladden the hearts of travelers, and provide a refreshing micro-world with its own ecology.

Some topics in this essay:
Pressure Life, Monument Valley, Liquid Water, Animals Animals, Temperature Life, Desert Biomes, Essential Elements, Hydrogen Sulfide, Energy Sunlight, Hot Deserts, life forms, desert plants, special adaptations, water available, liquid water, inches rain, hot desert, plants animals, sometimes life forms, eat insects, hot deserts, snakes eat lizards, networks roots lie, ten inches rain, mice kangaroo rats,