Describing the World

Continents

In the last article you learned how to divide the world into hemispheres. You can say in which two hemispheres a place is located. In this article we are going to learn a little about the continents, how many there are and a few interesting facts about each.

A continent is one of the seven main land areas on the Earth. Sometimes they can be a little confusing. Some are joined to each other, and some are completely surrounded by water. Some contain a lot of countries, and some only a few. Some people even like to argue that there are only six continents and not seven.

The Seven Continents.

So nobody can say I like one continent more than another, I am going to place them in alphabetical order.

Africa
Antarctica
Asia
Europe
North America
Oceania
South America

Look at the map. Which continents are joined together? Which are entirely surrounded by water?

Oceania (sometimes called Australia) and Antarctica are completely surrounded by water. The others are all joined to at least one other continent. Which continent is joined to two others? Every continent lies in at least two hemispheres, and some lie in three or four.

Using the map , see if you can name the hemispheres that each continent lies in. To help you, the number of hemispheres is written in brackets. Don’t forget the little piece of Asia on the left of the map!

Africa (4)
Antarctica (3)
Asia (4)
Europe(3)
North America (2)
Oceania(2)
South America (3)

Here are some interesting facts about each of the continents that make them unique (different to the others).

Africa

Contains the world’s longest river (The Nile).

Contains the world’s largest desert (The Sahahra).

Contains more countries than any other continent.

Most of the world’s gold and diamonds come from Africa.

Antarctica

Is the only continent completely covered in ice.

Is the only continent that is uninhabited by humans (although some scientists live there for short periods of time).

Asia

Is the only continent joined to two others.

Contains the world’s biggest nation (China).

Contains the highest point on Earth (Mount Everest).

Is the only continent where tigers are found in the wild.

Europe

Through colonization, at one time ruled almost all of the rest of the world.

Has been the starting point of both World Wars.

North America

Is joined to Asia by ice in winter (Bering Sea).

Is the only continent that lies entirely in the Northern and Western Hemispheres.

Contains the world’s tallest mountain (Mount Kea).

Contains the world’s largest fresh water lake (Lake Superior).

Oceania

Contains the fewest countries (Australia, New Zealand and Papua New Guinea)

Has more sheep than people.

Is the only continent that lies entirely in the Southern and Eastern Hemispheres.

South America

Contains the world’s Southern most city (Puentas Arenas).

Contains the world’s largest river system (The Amazon).

Activity

Take your ball from the previous lesson, about hemispheres.

Using different colored marker pens, try to draw the continents on the ball.

It isn’t easy to do, and the exact shape of each continent isn’t very important. Make sure that each continent stretches into all the hemispheres it is included in.

What We learned

There are seven continents.
Every continent lies in at least two different hemispheres.

What Are They & Why Do We Need Them?

We measure the day by saying that the sun is at it’s highest point at 12 o’clock, midday. Because the earth spins, as it travels around the sun, one half of the earth is in darkness and one half in light, all the time. This brings us to a problem. If it is midday where you are, on the opposite side of the earth, it is dark, so what time is it on the opposite side of the world?

Day and Night

Before time keeping and clocks were invented, people used to know approximately what time it was by watching the sun. If you look out of the window, at different times of the day, you will see that the sun is in a different place each time you look. This is the same everywhere in the world. Once clocks were invented, they simply had to look at a clock to know what time it was.

The earth spins on an imaginary line known as its axis, this movement is known as rotation. While it is rotating on its axis, it is also traveling around the sun, this movement is known as revolution. Although the earth is revolving around the sun, the sunlight only falls on the part of the earth facing the sun. So, the part facing the sun has day and the part away from the sun has night. As the earth rotates, different parts are exposed to the sun, and put in the shade.

• • Look at the two marks on the globe.
  • Notice that the one enters and leaves the sunlight before the other one does.

Check where the sun is shining right now.

The Problem

Remember the problem: if it is midday where you are it must be dark on the opposite side of the earth, it obviously can’t be midday, but what time is it? The earth is divided into time zones. The time is the same everywhere within one time zone, but different to all the other time zones.

How Time Zones Work

Because everyone wants to measure their day with the sun being at its highest point at midday, scientists came up with the idea to divide the earth into different time zones. There are 24 hours in a day, so there are 24 time zones. The time is the same everywhere within one time zone, but different to all the other time zones. When you move from one time zone to the next one, you change your watch by one hour. If you are traveling in an easterly direction you move your watch one hour forwards, if you are moving in a westerly direction you move it one hour backwards.

Example:

• New York is west of London, and they are separated by 5 time zones.
• This means that when it is midday in New York it is 5 pm in London.
• When it is midday in London it is 7 am in New York.

You can try this yourself, first read the instructions:

• Note the time on the clock. This is the time in London.
• In the right-hand box, select USA/Eastern USA.
• Watch how the bar moves to the left and the red spot shows -GMT 05:00
• Notice how the time has changed on the clock. It shows 5 hours earlier.

Now try it!

Extra Activity

There are 360 degrees of longitude on the earth, so what the scientists did was divide these by 24, that means that there are 15 degrees of longitude in every time zone. If you travel more than that, you have to adjust your watch. You may be wondering why time zones are measured in degrees of longitude and not miles or kilometers. See if you can figure it out for yourself, then check your answer.

More about time on this site

Describing the World

Hemispheres

When we learn about different areas of the world, there are different ways of dividing it up. We can divide it according to the globe, by cutting it in half across the middle or from top to bottom, these are called hemispheres. We can divide it according to land areas, or continents. It can also be divided according to languages spoken, climate, environment and economy. In this article we are going to look at the hemispheres.

The world is a sphere. It is shaped like a ball. The best way to represent the world is not by a map, but by a globe. How can we explain where anything is on the globe? We could say it is next to something else, or at the top or bottom, or even on the left or right, but these are not geographical terms. In geographical terms we have to describe position by using a compass.

The main points, or cardinal points, on a compass are North, South, East and West. The globe can be divided into half across the middle, or from top to bottom. Each of these halves is called a hemisphere. The word hemisphere means half (hemi) of a sphere. Because we can divide the ball two different ways, we can have four different hemispheres. Right and left, or top and bottom. Think about the cardinal points of the compass. What do you think we are going to call the hemispheres? If you are confused about where North, South, East and West are, go back and read the article on
compasses.

Activity #1

For this activity you need two oranges and a sharp knife.

Cut the first orange in half from top to bottom.
Cut the second one across the middle.
These are the two different ways you can divide the globe into hemispheres.
You have four hemispheres.

This can be a little confusing. Everyone knows that if you divide something into half, you only get two pieces. What you have to remember is that you can divide it into half either way, so you can make 4 hemispheres from a sphere. If you actually cut it with a knife, then you need two spheres to get your 4 hemispheres, but if you imagine the hemispheres, you can imagine all 4 on the same sphere.

Activity #2

For this activity you will need a plain colored ball, and a marker pen.

Take the ball and pen.
Put an X at the top of the ball and an O at the bottom.
Now draw a line from the X to the O across the front of the ball.
Mark the front of the ball with an F.
On the opposite side continue the line up from the O to the X.
Now you have divided the ball into two halves, left and right.
Find the middle of both lines. Mark them.
Draw a line around the center of the ball, through the points you marked.
Now you have a top and a bottom half.

Go back to the points of the compass. Do you think you can name your hemispheres? The top and bottom ones are easy. The top is North, and the bottom is South. With the front of the ball facing you, West is on the left and East is on the right (remember they spell WE). Write the letter in each of the areas.
Don’t forget that because you have marked all 4 hemispheres on the ball, you have divided your ball into 4, so 2 pieces will need each of the letters. Notice that each of the areas has two letters, either N or S and W or E.

Now we need to use a little grammar here. North, South, East and West are nouns, but we need adjectives to describe which hemisphere is which. So we call them the Northern Hemisphere, the Southern Hemisphere, the Eastern Hemisphere and the Western Hemisphere.

Look at your ball again.
Close your eyes, turn the ball around in your hands, and then place the pen on the ball, keeping your eyes closed.
Open your eyes and see where you placed the mark. Notice that it is in two hemispheres. If you used your hand instead of the pen, it could even fall into three hemispheres.
Which two hemispheres did your mark land in?

Now, put your ball away in another room and see if you can answer these questions:

1. How many hemispheres are there?
2. What are they called?
3. Which hemisphere is at the bottom of the ball?
4. Which is at the top?

These questions are a little more difficult, you may need to use the ball to answer these:

1. With the front of the ball facing you, which hemisphere is on the left?
2. What happens when you turn the ball around so that the back is facing you?
3. Now which hemisphere is on the left?

Don’t erase the marks on the ball, we are going to use it again in the next article

Bonus Activity for Older Students

Do you know that the lines you have drawn have geographical names? Do you know what they are?

The line running around the middle of the globe, dividing the Northern and Southern Hemispheres is called the Equator. It is shown on maps as 0 degrees Latitude.

The line dividing the globe into the Eastern and Western Hemispheres is actually two geographical lines. The one running down the front of the globe is known as the Greenwich Meridian. It passes through the Greenwich Observatory in London, and is measured as 0 degrees longitude.

The line dividing the globe into the Eastern and Western Hemispheres on the back of the globe is called the International Dateline. It is measured at 180 degrees West or East. It doesn’t matter which way you go around the globe, it is 180 degrees either way round.

When you placed the random mark on the ball, it fell into two hemispheres. There are two named places on earth that do not fall into 2 hemispheres. Can you think what they are?

Theoretically, any point that lies on the International Dateline, Greenwich Meridian or Equator, fall in one hemisphere only. It is also theoretically possible for a ship to be in all four hemispheres at the same time, if it was centered exactly over the equator on the Greenwich Meridian or International Dateline (both these points lie in the ocean).

Now answer these questions:

1. What is the line called which divides the Northern and Southern Hemispheres.
2. Can you name one country this line passes through?
3. Name the two lines dividing the globe into Eastern and Western Hemispheres.
4. Which two hemispheres do you live in?

The Antarctic is much colder than the
Arctic. On average temperatures in the Antarctic are 50-80 degrees Fahrenheit
lower than the Arctic. Although both areas receive the same amount of sunlight,
the ice and snow in Antarctica reflect much of the heat away, causing it to be
so cold. The winds also play a large factor in the temperature. Every increase
of 1.2 mph in wind speed drops the temperature a further 1.8 degrees Fahrenheit.
Even in summer a person’s breath freezes as soon as it leaves the body.

The Antarctic is also a desert. Even
though it contains 70% of the world’s fresh water, this has been built up over
thousands of years. The interior of Antarctica receives less than the equivalent
of two inches of rain each year. Of course, it doesn’t come in the form of
rain, but as snow. This makes inland Antarctica one of the world’s driest
deserts. The Air is too cold to hold moisture, which is why there is so little
precipitation. Even on the coast, where the temperatures are higher, there is
less than the equivalent of 15 inches of rain per year.

The Antarctic Peninsula, in West
Antarctica, directly south of South America has the highest temperatures. During
a really hot summer there, the temperatures can reach as high as 59 degrees
Fahrenheit, but the summer average is around 50 degrees. You can compare that to
the winter in Arizona. The average summer temperatures in the warmest place in
Antarctica are much the same as the average winter temperatures in the warmest
place in Arizona!

The cold in Antarctica makes it almost impossible for
humans to live there. Although the temperatures are so low, a person wearing
dark clothing can actually feel quite warm, as the clothes absorb the heat of
the sun. Any exposed skin, though, freezes. When it is frozen blood cannot reach
it and it dies. This is known as frostbite. The sun reflecting off the ice also
causes problems, and people must wear dark glasses outside or they may become
blind, from the ultra-violet rays. Add to the problem of the cold and sun, the
wind. Walking against such strong winds is very tiring. The combination of all
these factors is what caused so many explorers to fail to reach the South Pole
when they tried. In such cold climates humans must consume a lot of food to
maintain their energy. Early explorers often had to give up because they were
too cold, too exhausted and too hungry to go on. They had to carry or pull al
the food and clothing they needed on sleds. That meant spending more energy. It
was extremely difficult to make a balance between the energy needed to pull the
food (so requiring more food) and taking just enough food to give enough energy.

Related Articles:
Antarctica
Animals in Antarctica
Early Explorers in Antarctica
Penguins 

Continental Drift

#3: Recycling

By the early 1960’s it was established that the earth was making new
crust, on the ocean floor, all the time. However, since the earth is not
expanding, where is this new land going?

The answers began to appear in 1964, following a major
earthquake in Alaska. Geologists visiting the area immediately after the quake
were, at first, confused by reports about changes in sea level. Some areas were
claiming that the sea level had fallen, and others that it had risen. Despite
searching, the geologists could find no evidence of a crack in the earth’s
surface. A quake with a magnitude as great as this had to have an associated
fault line (crack), but where was it?

Barnacles

A particularly observant geologist noticed a strange
phenomenon. Along the entire coastline, there was a line of barnacles, still
living, way above the highest level that the sea reached. In some places it was
as much as 20 feet above the present levels of water. The fact that the
barnacles were still living meant that they had been in seawater recently. From
this, scientists were able to state that the sea level at the coast had
definitely fallen, or more accurately, the land had risen.

Inland Flooding

Further inland though, the story was the complete opposite.
Areas, which had been dry for years were suddenly sitting under water. There was
no doubt that these areas had dropped during the earthquake.

The Fault Line

By drawing diagrams, and making models, the scientists came
to the conclusion that the fault line must lie under the earth’s surface. The
areas of uplifting and sinking indicated that the line ran from an area just off
the coast, diagonally downwards, under the land. They also noticed that just
where their theoretical fault line was, there was a deep trench in the ocean
floor. Trenches like it can be found all the way around the Pacific Ocean rim.

Putting it Together

Now the scientists had the following information:

• The earth makes new crust on the ocean floor
• The crust moves outwards as newer crust is formed
• The earth is not getting larger
• There is a trench all the way around the Pacific Ocean
• There is a fault line running from the trench, under the land
  mass

It didn’t take them very long to decide exactly what was
happening to the extra land. It was disappearing down, under the
continents, at the trenches. The trenches are like a huge crack in the ocean
floor, where the newer rock slides under the older rock. As it slides, the
weight of the older rock pushes it downwards. Eventually it reaches the outer
core of the earth, which is extremely hot and molten. Here it heats up and
becomes molten, joining all the rest of the molten rock, to become magma again.

Recycling

In a way it is like a natural recycling plant. At the mid
ocean ridge, hot molten rock, or magma is forced upwards. As it comes into
contact with the cool ocean it solidifies, becoming new solid rock. The rock is
gradually pushed outwards my more rock as it forms. The entire ocean floor is
being pushed outwards towards the continents. At the edges of the continents,
the new rock is pushed downwards, under the continents. The solid rock heats up
and becomes magma again. Then the cycle begins all over again

Is That the End of the Story?

It might seem that the story is finished now. We have
successfully explained how the continents were pushed apart. We have proved that
the ocean floor is constantly being renewed. We have seen where the extra ocean
floor goes. However, it isn’t quite the end of the story. The theory of
continental drift once it got this far, became known as the theory of Plate
Tectonics. So now we need to look at Plate Tectonics, and also check those facts
about disappearing earth. Not all of it goes down under the continents, some of
it goes up!

Continental Drift

#4 Plate Tectonics

After 50 years of investigating, Wegener’s theory of Continental Drift became the fact of Plate Tectonics. The earth’s crust is made up of huge areas, all moving, known as plates. The edges of the plates, or plate margins, are where all the action is. Sometimes they cause earthquakes or volcanoes; sometimes they build mountains and sometimes the swallow up the earth’s crust.

The edges of the plates are known as the plate margins, or plate boundaries. Depending on the type of boundary, different things happen. There are three main types of Boundaries.

Spreading Boundaries

There are two types of spreading boundaries:

Ridges, where new rock is formed, pushing the plates apart, and Rift, where the plates pull apart, and the earth between them sinks.

On the ocean floor the plates are spreading. All along the mid ocean ridge, volcanic activity is pouring new lava out onto the seabed. As it hardens, it becomes new rock, gradually pushing the crust, on either side of it away. Another type of spreading boundary is the African Rift Valley. As the two plates are moving apart, the earth between them is becoming stretched. As it stretches it sinks, because it is thinner. It is a little bit like taking a piece of gum, and stretching it out. The pieces in your fingers stay thick, but the piece in the middle gets thinner and thinner, as it is stretched.

Converging Boundaries

Converging (coming together) Boundaries, are where two plates are banging into each other. What happens when they collide depends on the type of plate they are.

In a subduction zone one plate is being pushed beneath the other. It happens when a heavy plate hits a lighter plate. The heavier plate is pushed under the lighter one since it is more dense. This often happens where continents meet the ocean. As the heavier ocean crust is forced downwards, it takes water with it. The water causes the rock to melt at lower temperatures than normal. The pressure inside the earth is much greater than at the surface, it increases the deeper you go. The new molten rock tends to rise to the area of lower pressure, sometimes forming volcanoes. It is not uncommon to find volcanoes along a converging boundary, on the side of the heavier plate.

In a deformation zone the area where the plates meet is being crushed and pushed upwards. It happens when the two plates are almost equal in weight. Instead of one plate being pushed down under the other, they smash into each other, causing the edges to rise upwards. It is very similar to two cars crashing together, head-on. As they hit each other, the front ends crumple, and lift upwards. In this type of boundary huge mountain ranges are formed. The best example of this is the Himalayan Mountains. They were formed when the Indian Plate crashed into the European Plate. The two are still being forced into each other, and the Himalayan Mountains are slowly becoming taller.

If you think about it hard enough, you can probably see that plates with a spreading boundary on one side must have a converging or transverse boundary on the other side. The earth’s crust is moving and changing all the time, but the upward or downward movement of converging boundaries, stops the earth from growing larger. As the plates slip and slide over and under each other, they keep the size of Earth constant.

Transverse Boundaries

The last type of boundary is neither spreading nor colliding. The edges are sliding past each other, sideways. As they slide past each other they cause a huge crack in the surface of the earth. This crack, or fissure, is known as a fault line. Probably the best-known example of this is the San Andreas Fault, which is found in Western California. As they slide past each other they sometimes cause earthquakes. Areas with fault lines have more frequent earthquakes than other places.