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Africa for Kids
Exploring a Vibrant Continent, 19 Activities
By Harvey Croze
Chicago Review Press IncorporatedCopyright © 2006 Harvey Croze
All rights reserved.
The African Continent
The Vastness of Africa
Africa is huge. It is the second largest continent after Asia, and it takes up one-fifth of the land surface of the entire world. This fact is not always made obvious by maps. Most people are familiar with a world map based on the one made more than 500 years ago by Gerardus Mercator, a European mapmaker, for early explorers and their ship navigators. None of these Europeans knew very much about the world, and most of them rather selfishly thought that Europe and, after 1492, North America were the most important places on earth. So their maps projected a picture of the world that emphasized the northern hemisphere of the globe.
The Mercator map is the one still used in most classrooms around the world. However, while it is good for plotting courses across oceans, the Mercator map is terrible for estimating size. Africa looks only slightly larger than the United States. But take a look at a globe or an image taken from a satellite. Africa fills nearly a whole side of the globe. That's the trouble with maps of large areas that present a curved surface on a flat piece of paper.
There are some paper maps that display comparative area sizes better. Imagine making a map by peeling off the surface of the earth like the skin of an orange and laying it down flat on a page. Such a map is called an equal area projection because all of the continents and countries are shown in their true relation to one another. The big ones look big, the small ones, small.
Africa is the oldest continent. Most of the land has been in the same place for over 550 million years, and some of it since the beginning of life itself, 360 billion years ago. Does that mean the earth is a pretty stable chunk of rock? Not really. In fact, most of the surface of the earth is made up of a dozen gigantic slabs of rock called "tectonic plates" that are actually floating on the earth's softer, hotter center. Up until about 200 million years ago, all of these tectonic plates were clustered together into one large landmass called Pangaea (pan-GAY-ah).
The earth was very unstable back then, its surface heaving with great volcanic eruptions. Pangaea began to break into two pieces 180 million years ago. One, called Laurasia (lawr-AZE-ee-ah), floated north; the other, Gondwana (gone-DWAH-nah), stayed in the south. At this time Africa was attached to South America, but Antarctica had already begun to drift away to the south. The separation of South America, Africa, and Madagascar began some 115 million years later.
How do we know that the continental drift happened? First of all, geologists have found ancient rock formations in Brazil that are similar to some found in west Africa. Other formations in India, Australia, and Antarctica are like some found in East Africa and Madagascar. Second, a number of plant and animal species, both living and fossilized, can be found on more than one continent. It is unlikely that all of them crossed thousands of miles of ocean by accident. These similarities help prove that the continents were once, long ago, all attached. And finally, look at the shapes of the modern continents. If the clock were to run backward, it is easy to imagine how South America might fit into the southwestern kink of Africa and how Antarctica, Madagascar, and India tuck neatly along Africa's eastern side.
While all these monstrous movements were taking place, Africa pretty well stayed put in the middle of things as the other chunks drifted away. Much of the southern half of Africa is where it was in the beginning. The Sand River rocks (technically called gneisses [g-NEE-ses]) of northern Transvaal (trahns-VAHL; roll the r) formed about 3.8 billion years ago and are nearly as old as the earth itself. Some of these formations are exposed, and there are places where you can have a picnic right on top of the oldest rocks in the world.
Despite its vast age, Africa is still changing, from drifting sands in the Sahara Desert to erupting volcanoes in the Great Rift Valley. What are the controlling factors of these movements, the things that determine the formation of the land?
Rock and Dirt: Geology and Soils
Every once in a while, even today, the earth produces signs that it has not finished forming. A city crumbles in an earthquake, a new island appears in the middle of the sea, or a volcano erupts on land. These sorts of events happened all the time when the earth was young, and they have been important ways for minerals to get from the earth's interior to its surface.
Most African soils are volcanic, meaning they were formed from rocks and ash that have been blasted out of volcanoes. These soils are particularly rich in minerals. Minerals trapped inside rocks are pretty useless as food for living beings. If they can get free, they can become food for plants and animals. Energy is needed to break down rocks, like the eroding energy of running water or the heating and cooling energy of the sun. Africa has had plenty of both over the earth's history, particularly in ancient times when even the Sahara Desert had plentiful rainfall.
Water makes the land. What does that mean? It means that millions and millions of years of rainfall and running water have worn down the rocks that make up the earth's surface and shaped the landscape. The rainfall that gathers in rivers gradually carves its way deeper into the rock and creates interesting topography. Just look at the Grand Canyon.
Minerals are freed from rocks through erosion. Erosion describes the movements of rock and dirt as water runs downhill. Erosion by water and wind over very long periods is called "weathering." Weathering exposes minerals at the earth's surface and then helps break them down into soil.
Depending on the steepness of the slope, the kind of soil, and the amount of vegetation, different amounts of water soak into the soil. After the water soaks into the soil, plant roots make good use of it. If the soil is porous, some of the water continues downward until it accumulates in aquifers or underground rivers.
Investigate Soil Erosion
Dirt plus water equals ... a mess! Be sure to do this muddy activity outdoors.
Dirt is just dirt? Not so when it comes to soil erosion. Explore the ways different soils erode. You are going to "make it rain" over two or three slopes with different soil types to see which type is more susceptible to erosion.
Adult supervision required
3 shallow boxes. The ideal size is 3 feet long by 2 feet wide by 4 inches deep, but anything close will do, as long as the boxes are shallow and can be sealed to hold soil.
3 different types of soil — enough to fill the boxes to ½ inch from the top. For example, humus-rich dirt dug up from under the leaf litter of a wooded plot or from under a big old shrub in a garden (get permission!); a clay soil like the yellowish stuff around a building site (clay soils tend to feel a bit slimy between the fingers when wet); a sandy soil (if you live near a sandy beach, most soil on the land side of the dunes will be sandy; otherwise, just use pure sand from a building site or a sandbox)
Scissors or Exacto knife
Access to outdoor stairs or a folding chair and a couple of pieces of wood or building blocks (choose materials that you don't mind getting wet)
3 large (quart size) jars or other large glass or clear plastic containers
A bathing suit or clothing you don't mind getting wet in
Garden hose with an adjustable spray nozzle. If a garden hose is not available, a watering can or a bucket of water poured through a large kitchen sieve will work
Stopwatch or watch with second hand
A willing assistant
Felt-tip pen or marker
20–30 sticks, about 8 inches long
Repeat the steps below for each soil type. Treat each soil the same way. Make sure no soil type is wetter than the others and pack each down to the same density.
1. Fill one of the boxes with soil to about ½ inch from the top. Pack the soil lightly by slapping it down with the palm of your hand. Don't pack it too tightly. You should be able to easily stick your fingers through the dirt and touch the bottom of the box.
2. Carefully tear or cut out a narrow V-shaped piece about one-third of the way (1 to 1½ inches) down one corner of the box to create a "drain," so that water running over the soil will accumulate and exit from that corner.
3. Prop up the box on an angle. The easiest way is to lay it lengthwise across two stairs. Position the lower end on the second stair protruding over the edge so that a jar will fit under the corner of the box.
Another option is to use a chair and a block. Position the box so that the high end is elevated not less than one-third of its length. Jiggle the box's position so the "drain" is the lowest part of the box by one to two inches and the box protrudes enough to get a jar underneath.
4. Get the water gear together. If you have a hose with a nozzle, adjust it so that the hose produces a medium-to-coarse spray, just like raindrops in a good shower. If the hose does not have an adjustable nozzle, make an even spray by partially closing your thumb over the end of the hose. If you are using the bucket- and-sieve method, ask a friend to hold the sieve while you pour. Practice on the grass or pavement with any of the three methods until you are confident you can produce an even flow of water for about 20 to 30 seconds (as long as it takes to fill up the jar).
5. Place the jar under the "drain" and "make it rain" as evenly as possible over the soil. Keep making rain (even if you have to pause and fill up the bucket) until the jar is full.
6. Label the jar with the masking tape and felt-tip pen according to the soil type it drained: humus, clay, or sand, as appropriate.
7. Place the jar to one side and repeat the steps for each soil type.
8. Compare the water samples. Is there a difference in their turbidity (the cloudy quality of water produced by the soil sediment)? What can you conclude about which soil types are more vulnerable to erosion?
Since you have the materials set up and are already wet, you can also test the role of vegetation cover in controlling soil erosion.
You will need additional materials to simulate vegetation. Get some old plastic bags and 20 to 30 (depending on the size of your soil box) sticks about eight inches long. Cut the bags into 20 to 30 small, three-by-three-inch squares, and poke the stick through their middles to make little artificial trees.
Repeat the preparation in steps one through six above, using the soil type that showed the most loss from erosion. But this time, before you "make it rain," plant the little artificial trees so that they make a canopy that covers at least half the area of the soil bed.
Now compare the turbidity of the water samples with and without vegetation cover. Can you see a difference? Can you imagine how cutting down trees over thousands of square miles has affected Africa's soils?
Be sure to clean up the steps, chair, buckets, and jars after the experiment!
In the dry areas of Africa, there is usually too little vegetation to break the fall of rain. During the wet season downpours, raindrops smash onto the bare soil, loosen the particles, and carry them off the land, along depressions, down little gullies, and into creeks, small rivers, big rivers, and at last the sea. Soil erosion is a huge problem in Africa and has been for a long time. The accumulation of silt at river mouths can be a mile thick.
Most of the minerals that crumble off the rocks pile up as young rocky soil. Then, slowly, sun and rain, heat and cold, natural acids made from water mixing with chemicals in the soil, and the roots of plants wriggle their way into the cracks in the rocks and the rocks crumble, mix with the organic debris, and eventually become soil.
Soil tends to display the characteristics of the parent rocks from which it came. Some soils, like those that come mainly from volcanoes, are very rich in minerals because they originated deep in the earth. Many volcanic soils in East Africa today are being washed into rivers and then into the sea at the rate of two to three inches per year. In 100 years, some places will have no soil left at all, only the underlying rock. Other soils, like the ones derived from granite rocks, are stony and poor in nutrients.
Over time, the chemical composition of soil may change as animals from earthworms to elephants add their dung to the soil. Soil can also move vast distances by the action of rivers. The Nile River carries soil along its 4,000-mile length, from the Ethiopian mountains and the East African highlands through Egypt to the Mediterranean Sea. As the river water flows into the sea, soil particles settle and produce a great mudflat — a delta — spreading out from the river's mouth. Because the soils of the Nile Delta were so fertile, agriculture flourished as long ago as 12,000 B.C. and became the basis of the ancient Egyptian civilization.
Climate: Seasons and Rainfall
Forget about the four seasons in Africa. Although there may be a few weeks of snow on the tops of the Atlas Mountains in Algeria in December or the Drakensberg (DRAH-kens-bairg) Range in South Africa in July, there are no winter or summer season in Africa as Americans and Europeans know them. And without winter and summer, there's no equivalent of spring or fall.
In Africa, there are basically two seasons: wet and dry. What's important is how much rain falls to the earth. Plentiful rainfall is required for agriculture, and therefore human economies and livelihoods ultimately depend on it. Even modern irrigation in deserts uses water from rain that fell elsewhere.
Most African countries, especially those in western and southern Africa north of the Limpopo (lim-POE-poe) River, have one rainy season and one dry season. The northern part of Mali in west Africa, on the edge of the Sahara, gets only five inches of rain per year. Others, like the eastern African countries Kenya and Tanzania, are influenced by monsoons and may get 40 inches in two rainy seasons, with the wettest times in April and November. In the far north, in Tunisia (toon-EEZ-ee-ah), for example, and in the most southern region of South Africa, the climate is called "Mediterranean," with a cool, wet winter and long, hot summer. In the Congo, along the equator, it rains most of the year, a total of 80 inches, almost seven feet of rain!
The E1 Niño rains started in October 1997 and ended in mid-April 1998: six months of disaster in Kenya. People and animals drowned, crops were flooded, and bridges and roads were spoiled by the deluge of water. Even today, many of the roads have not been repaired in the poorer areas of the country. Waterborne diseases such as cholera, dysentery, typhoid, and bilharzia increased due to the rains. In a developing country such as Kenya, people have a hard time finding the money to rebuild their homes. Where crops and farms were destroyed, others also lost their jobs. With global warming, the floods will only get worse.
— Julie Nailantei, a Kenyan teenager
The big difference between the rainfall in most African countries and most of the world is not so much the amount but the way it's distributed over the year. Washington, D.C., gets the same amount of rain in a year as Nairobi (nahee-ROW-bee), the capital of Kenya — a total of about 40 inches. Washington and Nairobi are both woody and green. But while Washington stays that way all year round (the grass even remains green under the snow in the winter), the grass in and around Nairobi dries up and may even burn in wildfires each year. The difference is that in Washington it rains a little bit at least once a month; in Nairobi, the rains come crashing down, mainly in April. Much of the water can't be absorbed by the soil and runs off into the Indian Ocean.
Excerpted from Africa for Kids by Harvey Croze. Copyright © 2006 Harvey Croze. Excerpted by permission of Chicago Review Press Incorporated.
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