|Publisher:||Chicago Review Press, Incorporated|
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|Age Range:||6 - 9 Years|
About the Author
Nancy F. Castaldo is a former environmental educator and the author of Oceans, Rainforests, Rainy Day Play!, Sunny Days and Starry Nights, and Winter Day Play!
Read an Excerpt
An Activity Guide for Ages 6-9
By Nancy F. Castaldo
Chicago Review Press IncorporatedCopyright © 2004 Nancy F. Castaldo
All rights reserved.
Close your eyes and imagine yourself in a desert. In the desert of your imagination you might find yourself under the sun and standing on hot sand. You might look up to see sand and rocks in all directions. At night the sand becomes colder and the cloudless sky becomes full of stars. Well, that is what you will find in many deserts, but not in all of them. About one-fifth of the surface of the earth is desert. Most deserts are just as you imagine — hot — but others are very cold. However, all deserts have one thing in common — very little rain.
The Biologist's View of the Desert
There are many ways to define a desert. Meteorologists define the desert by the amount of rainfall (or precipitation) it receives each year. By definition, a desert is a place that receives very little rain. In fact, the rain must be less than 19.7 inches (50 cm) each year. Look at a yardstick and see if you can find the 50-centimeter mark on the metric side. You'll see that it's an extremely small amount of rain for one whole year. Compare that to the total amount of precipitation for the Albany, New York, area in 2002 at 40.8 inches (103.6 cm), and you'll see that the desert receives a much smaller amount in one year. (What is the annual precipitation in your town?) Biologists look at rainfall when they define a desert, but in addition they look at the evaporation rate. Evaporation is when a liquid changes into a gas; in this case, the liquid is the rain. The evaporation rate describes the time it takes for the rain to dissipate into the air. The evaporation rate must be greater than the amount of rainfall for the region to be called a desert by biologists. Basically, biologists focus on the little amount of rain deserts receive each year and the fact that most of that rain evaporates and is not beneficial to the animals and plants that live in the region.
What Makes Most Deserts So Hot?
Why are most deserts so hot? Most deserts fall between the latitudes called the Tropic of Cancer and the Tropic of Capricorn. If you look on a globe, these latitude lines are found on either side of the equator. This region is known as a subtropical climate belt. Generally it has dry air and clear skies. The winds are very dry because they have lost most of their moisture in the more northern or southern regions. These deserts are often described as hot, dry deserts. The winds along their western coasts are often cooled by cold ocean currents, which cause them to drop only a small amount of water. These areas are called coastal deserts. Atacama, in Chile, is an example of a coastal desert.
Some deserts are found far inland or between mountains. Often these are known as semiarid deserts. Semiarid deserts are found in Utah, Montana, Russia, and northern Asia. The winds that reach these deserts have usually released most of their moisture before reaching the desert areas.
Desert regions also absorb more heat than humid regions. Since there is not much to deflect the sun's rays (bounce the rays off of the ground) in the desert, the desert absorbs 90 percent of the sun's rays, or solar radiation, which heats the ground and the layer of air above the ground. In more humid regions of the world the sun's rays are deflected by clouds, dust, and water.
In order for rain to fall there must be clouds in the sky. Clouds rarely float over the desert, but once in a while a cloud does float over the desert and rain falls to the hot ground below. Sometimes the ground is so hot that there is a layer of hot air just above the ground. This air can be so hot that it evaporates the rain as soon as the rain hits it. The rain never reaches the dry earth of the desert. When this occurs it is called a ghost rain. Sometimes a ghost rain cools the layer of hot air enough so that if a second rainfall occurs, this rain will not evaporate and will have a better chance of falling to the ground.
Make a Solar Still
Plants and animals that live in the desert have adapted to the lack of rain in very unique ways that we will explore further. People, however, do not have these adaptations. They have to obtain water or they will die. A person can live only about three days without water when the temperature is above 100ºF (37.8ºC), as it is in the hot and dry deserts.
There are only a handful of ways to obtain water in the desert. You could try to collect rainwater or dew in the morning. You could also get water from desert plants, like cacti. Another way to obtain water is to build a solar still. The solar still was created by two doctors and was tested by the United States Air Force in the deserts of Arizona. Here's how to make your own.
What You Need
* A grown-up to assist
* Measuring tape
* Glass jar, such as a 32-ounce (.9 liter) mayonnaise jar
* Plastic wrap
What You Do
1. Dig a hole roughly 3 feet (.9 m) across and about 2 feet (.6 m) deep.
2 Place the open jar in the center of the hole with the opening on top.
3 Ask someone to help you spread a large sheet of plastic wrap over the hole and jar.
4. Place stones on the plastic wrap on the ground to hold it down, and place one stone in the center of the plastic wrap covering the jar opening to hold the plastic wrap securely over the opening of the jar. Water will eventually gather in the jar through the process of condensation. Condensation occurs when the water vapor in the air is pulled out and turned into liquid water. You might get a pint of water in about 24 hours.
If you were trying to survive in the desert, your body would require about seven to eight pints (3.3 to 3.8 L) of water each day you are exerting energy. You could probably last about five days without water if you didn't exert any energy at all. That means no walking, not even at night. Look at the water you gathered in your still. Would it be enough for you to survive until you are rescued? Would it be enough to sustain you walking at night to search for help?
The still not only collects water, it purifies it. Here's something important to remember if you are making your still in the desert and you have no other water: One still can keep you alive; making more stills will keep your friends alive as well.
People of the Desert
It is difficult to imagine people living in the extreme conditions of the desert. While people are not built for life in the desert, they have found ways to adapt to life in deserts around the world for thousands of years. How do these people protect themselves from the harsh climate? Just as hair or fur can benefit desert animals, clothing sometimes protects people from the extreme temperatures of the desert.
What do you do when you are very hot? You might put on a bathing suit or shorts and a T-shirt to cool yourself down. Some desert people wear very little clothing, but some others put on loose-fitting, flowing garments that shield their bodies from the heat and cold and also help to reduce evaporation through the skin. In the following chapters you will see how the different people of the deserts have adjusted to the harsh desert conditions.
Wind and Water at Work
Deserts have dramatic landscapes with many unique land formations. There are rugged cliffs, giant sand dunes, rock columns and arches, and colorful canyons. With little soil or vegetation to offer protection, these spectacular formations are often caused by winds ripping across the desert, carrying sand and gravel that cuts and carves out desert landforms. Some of these landforms, such as the Rainbow Bridge National Monument in Arizona, are so dramatic that they have become world-famous attractions for visitors from all over the world. The Rainbow Bridge, made of sandstone, is the world's largest natural bridge and spans Bridge Canyon. Can you name any canyons or other landmarks that attract a lot of visitors?
Let's take a look at some other landforms. You might have heard of mesas and buttes. These two types of formations are sometimes used as landmarks by desert travelers. In the vast desert landscape they help travelers identify their locations. They also help to produce some of the desert's spectacular scenery. Both mesas and buttes jut out of the flat desert toward the sky. Mesas are large plateaus that have steep sides and look a little like flattened mountains. When mesas erode they become buttes. Buttes are smaller, isolated forms that also have steep cliffs or slopes.
Other landforms include playas and salt flats. Playas are temporary lakes that form in the desert. When these lakes dry up they form salt flats. We'll take another look at salt flats on our journey to South America.
To survive the harsh conditions plants face every day in the desert, they must adapt in various ways. They may not have to compete for light and space, as they do in the forest, but instead they must compete for water. Some plants store water, while others can locate underground water. Still others have adapted to living with very little water.
Most plants in the desert seem to hug the ground. Unlike the rainforest, where there is a large canopy of leaves and layers of plants, the hot, dry desert has mostly low-growing shrubs and short, woody trees and plants, such as cacti and mesquite. Being close to the ground helps these plants retain moisture so that the wind does not dry them out, which would happen if these plants were taller.
Sagebrush, a low-growing plant and Nevada's state flower, is common in the semiarid deserts of Utah and Montana and, of course, Nevada, where it carpets the ground for miles. Sagebrush is also found in cold deserts.
Coastal deserts have plants that have adapted with stems that swell when water is available and shrink when it's not. Most of these plants have roots close to the surface that can soak up rainwater before it drains into the ground. Plants that grow in these deserts include rice grass, little leaf horsebrush, black sage, and saltbush. All of these plants have individual adaptations. The saltbush, for example, has the ability to continue making sugars in extreme heat, when most plants shut down their food processes.
You can't say that desert plants don't have attitude, because they really do. There are other plants that protect themselves from animals that can eat them, but not many go so far as to grow spines that say, "No munching here," such as cacti. Cacti are part of the group of desert plants known as succulents, and they range in size from 50-foot (15.2-m) saguaros to cacti that are the size of a thumbnail, such as the Blossfeldia liliputana, which only grows about a half inch (1.3 cm) across. All cacti are succulents, but not all succulents are cacti. Succulents have thick, fleshy stems or leaves that store water. Cacti grow in hot, dry deserts and semiarid deserts. Typically cacti have round or cylindrical shapes and spiny surfaces. These spines protect the plant from munching animals. Spines can also help keep the cactus cool. In this activity you will make your own cactus model to see how this happens.
What You Need
What You Do
1. First, mold your clay into the shape of a cactus. You can easily form the shape of a barrel cactus by making a ball of clay, then flattening the bottom so that it can stand up on its own on a flat surface.
2 Shine the flashlight on the cactus you formed. As you will see, all of the light reaches the surface of the cactus, just as the sun would in the desert.
3 Now start adding toothpicks to the cactus to form the spines. Poke the toothpicks all around the surface of the cactus.
4 Shine the flashlight on the spiny cactus. Does all the light reach the surface of the cactus? Can you see how the spines of the cactus can shade a cactus and keep it from overheating and getting burned by the sun?
Some cacti, such as the hedgehog cactus and barrel cactus, have a dense covering of silvery spines. The spines not only provide shade for the cacti, but their color also helps to deflect the sun's rays from the cactus plant. In addition, some cacti have very small jets between their spines that spray water from within the cactus to its surface. This acts like a sprinkler system to help cool the plant in the hot desert sun.
Create a Cactus
You can actually create your own cactus with a method that gardeners use called grafting. Grafting is a process that adds one plant to another plant to develop a new plant that is unique. Sometimes this is done to save a plant that is in danger of dying, and other times this is done to create a unique variation. Sometimes certain kinds of cacti are difficult to grow and it's easier to obtain the plant through this process. This project should be done in the summer when the cacti are in their growing season.
What You Need
* A grown-up to assist
* 2 different cactus plants
* A clean, sharp knife
What You Do
1. Pick out the cactus that will be the base for your new plant. You will need a grown-up to cut the top off of that cactus. The base should remain rooted in the soil.
2 Ask a grown-up to cut the top of the other cactus off, making sure that both cut areas are about the same size.
3 Place the top of the second cactus on the bottom that is still rooted in the soil. Line the two portions up so that they match pretty well.
4 Insert a toothpick to hold the two together. Place the new cactus in a shady spot for a couple of days.
5 After a couple of days, place your new cactus in a sunny spot and follow your regular cactus care. Make sure not to pull the pieces apart to check them.
6 Allow about two weeks for the cacti pieces to become fully grafted.
There is a custom of people bringing a candle, a loaf of bread, and some salt to the owners of a new house. The candle signifies that there should always be light, the bread symbolizes that there should always be food, and the salt symbolizes the spice of life everyone needs. The Hopi Indians of the American Sonoran Desert have their own custom. They put pieces of cactus in the corners of each new house to "give the house roots." Can you think of any customs like that in your family?
Sandy Soil Experiment
Plants that grow in the desert must not only adapt to the heat, they must also adapt to sandy soil. Try this experiment to see what happens to seeds in sandy desert soil.
What You Need
* 2 small terra-cotta pots
* Garden soil
* Lettuce seeds
What You Do
1. Place sand in the first pot and ordinary soil from your garden in the second pot.
2 Plant the lettuce seeds in each pot and water.
3 Place the two pots on a sunny windowsill and water them every three to four days.
4 Keep a record of the plants' growth. What do you notice? Does one grow faster than the other? How often do the pots dry out?
Animals Also Make a Home in the Desert
There aren't many large animals that live in deserts because most animals are not able to store enough water and tolerate the heat. Instead, in the hot and dry deserts there are mostly small animals like kangaroo rats and other animals that can burrow or dig into the ground during the day and come out at night when it's cooler. Of course, there are always exceptions.
Each desert has its own variety of animals. Badgers and coyotes are able to live comfortably in the semiarid desert regions. They're joined by owls and eagles. Kangaroo rats, jackrabbits, gerbils, and a few species of mice also make their home in desert regions. Many reptile and insect species have also adapted to the extremes of desert weather.
Excerpted from Deserts by Nancy F. Castaldo. Copyright © 2004 Nancy F. Castaldo. Excerpted by permission of Chicago Review Press Incorporated.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Table of Contents
1 Discovering Deserts,
2 Welcome to the Wild West,
3 South of the Border,
4 Journey to the Sahara, Namib, Kalahar, and Negev,
5 The Red and Black Deserts of Asia,
6 Deserts Down Under,
7 Arabian Days and Nights,
8 Not All Deserts are Hot,
9 Saving the Sands,