Look carefully at the cast and try to draw the leaf or the bone as it really was.
- What are fossils?
- Why were the animals long ago different to animals we can see nowadays?
- How do fossils form in rocks?
- Why are fossils so important?
- What is the Cradle of Humankind in South Africa? Why is it a World Heritage site?
Chapter 4 deals with fossils - the shapes that are left in the rock when a plant or animal has died there and been covered with mud, and body fossils where the remains have been preserved over time. This chapter also deals with the importance of fossils and is a good chance to highlight the significant role that Africa and particularly South Africa has played in documenting the history of life on Earth, and the important fossils which have been found in South Africa. If you are based in Gauteng, you are well-placed to go on a school tour to the Cradle of Humankind at Maropeng and visit the museum which delights children and adults with its interactive display.
Fossils in rock
These old photographs are of fossil hunters! These people are splitting open pieces of shale. They are looking for fossils in the rock. The layers of the shale split apart, and occasionally reveal the shape of a leaf or an animal in the rock. The shape is called a fossil.
All over the world, people find fossils of leaves and bones in the layers of sedimentary rock. These leaves and bones came from plants and animals that lived millions of years ago. They were not like the plants and animals we see today.
Fossils are the preserved remains of dead plants and animals
A fossil may look the same as the plant or animal when it was alive, but it is not the real leaf or bone you see. The fossil has changed to stone through a special process, and the stone has kept the shape of the leaf or the bone. This rock shape is called a fossil, or a body fossil.
Below you can see a photo of a fossil of the head of a dinosaur, and the next image shows you what scientists think this dinosaur looked like.
This fossil of the dinosaur's head is not the actual bones, but it is actually now a rock in the shape of the dinosaur's bones. Over millions of years, the bones turned into rock. So, a fossil is the remains of an ancient plant or animal which has been preserved in a rock. Most of the organisms that paleontologists study are now extinct. This means that they are no longer alive today.
Why are fossils so important?
The Earth's past is fascinating to us! Imagine being around when all the dinosaurs were walking on Earth. As humans, we want to find out about Life's History on Earth.
In recent history, we have books written that record what happened. This means we can read what people who lived long ago wrote about that time period. But no human was around millions of years ago to record what happened then!
So we have to use other ways to find out about what life was like on Earth millions of years ago. To do this, scientists use fossils! Fossils are actually our most valuable source of information about the ancient past!
But what can fossils tell us about life long ago? Fossils tell us about the organisms that lived long ago. Imagine the first scientists that discovered a dinosaurs bones! These bones were much bigger than the bones of any other animal on Earth today! This immediately told the scientists that the animals from the past were really big!
Fossils can tell us much more than just which organisms lived millions of years ago. By studying fossils of plants and animals, scientists can also gather information on how these organisms grew, what they ate, the environment they lived in and even some aspects of their behaviour and how they interacted!
For example, studying fossilised faeces of an animal can give evidence about what an animal used to eat.
By working out which plants used to grow during a particular time period in Earth's history, scientists can work out what the climate was like during that time. We now know when there were ice ages where the whole Earth was covered in ice for thousands of years, and when it was warmer and there were droughts.
A fossilised footprint can tell lots of things about a prehistoric animal, such as how much it weighed, how big it was, and even what speed it was running at!
The layers of rock which are lower down will be the oldest as they were deposited first. So the fossils in these layers will be from earlier times than fossils in rock layers which are closer to the surface.
How did the bodies of animals and plants get into the rock?
Have you perhaps seen the body of a dead bird? Dogs, flies, ants and beetles all take away the parts of the body. The wind blows away the feathers and soon there is nothing left to see.
But sometimes it does not happen like that. Imagine an animal died in a river. There was a flood and the river quickly covered the body with sand. In years after that, more floods brought more sand and put it on top. The heavy sand pressed down on the bottom sediments. Slowly, the bottom sediments became sedimentary rock.
Let's try make our own model to understand how fossils are formed in sedimentary rock!
How to make a model of a body fossil
Fossil-hunters look for fossils in sedimentary rock. They never know whether they will find a fossil or not. They have to split open the rock layers to see any fossil. You are going to make a model of some rock that you will split open.
You will need to mix the plaster of Paris and get it ready for the learners. Show the learners how you do it, because this is part of their technology knowledge in the processing strand. Mix enough for two or three groups at a time, because it starts to set (harden) quite soon after you add the water. If you cannot get plaster of Paris, then get screed mix from a building supply shop. This is cement, mixed with very fine sand. Another material you can use is putty, also from a building supply shop or hardware store. Mix cement powder or Polyfilla with the putty to make it harden quickly. A fourth material you can use is salt dough. You mix a cup of cake flour with half a cup of water and add a teaspoon of salt. Mix the flour and water until you have a stiff dough that you can shape. Finally, a material you can use is river clay; make it stiff so that it can keep the shape of a bone or leaf. Let it harden in the sunshine.
- small container: a plastic dish that you can cut up, or the bottom of a milk carton
- a leaf with ribs that stand out, or
- an animal bone, for example, a chicken bone
- a little Vaseline
- plaster of Paris
Each group must make a model rock with a fossil.
Of course, it's much more fun if every child can make his or her own fossil, so try to arrange the lesson for this to happen.
- First, spread Vaseline over the back of your leaf, or your chicken bone.
- Next, take your cardboard container to your teacher. Pour the fresh plaster of Paris mixture into the container. The plaster of Paris will begin to set hard in about 10 minutes, so you must be ready with your bone of leaf.
- Now put your leaf or bone onto the top of the wet plaster of Paris, and press it gently into the plaster. The bone must go in only half-way as you see in in the picture below. The leaf must go only far enough to leave the shapes of its ribs in the plaster.
- Leave the plaster to set (to get hard). Notice how hot your container becomes while the plaster is setting.
- First, pull out the leaf or the bone. It will come out easily because the plaster does not stick onto the Vaseline.
- Now you have an impression of the leaf or the bone. An impression is like a footprint in mud.
- Next, spread a very thin layer of Vaseline into the impression and around the impression, as you see in the picture below.
- Then collect some runny wet plaster of Paris from your teacher and pour it over the Vaseline to cover the old plaster and fill the container almost to the top. Let the new plaster set for a day.
- Tear off the cardboard or plastic container from the plaster "rock" you have made. The fossil is hidden inside. You can paint the plaster to look like a rock.
Note that the mould has been turned upside down to get this out.
- Now give your "rock" to another group and get a different rock from them. Do not tell the other group what fossil is in your "rock".
- Use the knife to tap gently on the edge of the "rock". Use a stick to tap on the back of the knife blade, so that you do not hit too hard.
- Your "rock" should split open if you tap in the right place. When it splits open, you will see a cast of a leaf or a bone on the top layer. The cast has the shape of the impression, but the impression goes inward and the cast stands up.
Look carefully at the cast and try to draw the leaf or the bone as it really was.
Try to work out what kind of plant the leaf came from, or what kind of animal the bone came from.
Is the cast (the shape) really a bone, or really a leaf?
No, it has kept the shape of the bone or leaf.
Do you remember learning about plaster of Paris in the second term in Matter and Materials? What properties of plaster of Paris make it useful in this activity?
The plaster of Paris is wet and soft when you first mix the powder and water together. This is useful as it allows you to mould the plaster of Paris around the bone like the mud from long ago would have done. The plaster of Paris then sets and becomes very hard just as the mud and rock did over time. This is useful as it forms a cast of the bone which is hard and set.
Now that you have seen you an impression of an object can be made by using plaster of Paris, let's have a closer look at how a dinosaur fossil was made millions of years ago.
Look at the pictures below and read the explanations for each stage of the fossil formation process.
Long, long ago, a dinosaur dies on the banks of a river, such as this triceratops in the picture.
The flesh of the dinosaur decomposes, or other animals eat it. So, only the skeleton remains.
There was a flood and the river rose and covered the skeleton with mud and sand.
Over time, more floods deposit more layers of sand and mud over the skeleton. Over thousands of years, the bottom layers start to become compacted and turn into sedimentary rock. Under the ground, water carried substances from rock into each little space where a bone had been. Rock took the place of bone. We say the bones were fossilised. A fossil bone has the same shape as the original bone but much heavier.
Millions of years later, the conditions of the environment above the skeleton may change. The rock is eroded and weathered over time by wind and water and the fossil is exposed on the surface. A scientist sees the fossil and a great discovery is made!
Other scientists join in and they excavate the fossil by carefully removing the rock and sand around the skeleton. The fossils will be carefully packed and taken to a museum or research centre where the scientists will study them to see what they can learn about prehistoric life. They will try to reassemble the bones into a full skeleton - this may take many months to do!
Body and trace fossils
We have seen many different fossils so far in this chapter. These fossils can be divided into two groups:
- Body fossils
- Trace fossils
A body fossil shows you the shape of the body of the plant or animal. Body fossils include teeth, bones, shells, stems, leaves and seeds.
Sometimes an animal left only a sign that it has been there. For example, if you walk across wet cement, you might leave a footprint which will be preserved in the cement when it hardens. Look at the picture below.
We said that body fossils are the preserved remains of the body of an animal or plant. So what about things like fossilised footprints? Fossils of footprints, egg shells, and nests, for example, are all remains of the activity of an animal. We call these trace fossils.
Some ancient animals, like dinosaurs may have walked across wet mud and left footprints in the mud, like in the picture below. The dinosaur leaves a trace behind. Over millions of years, this footprint can be preserved and become a trace fossil.
Use the diagram below as well as your previous knowledge of how sedimentary rock forms to write captions for each stage of the formation of a trace fossil.
Trace fossils were also made from animals nests, eggs and droppings.
A body fossil would be in the form of the organism that has fossilised. A trace fossil indicates evidences other than a fossilised body part, that indicates the existence of an organism, such as burrows, trails, eggs, nests, and fecal matter (dinosaur poop).
Some fossils of ancient organisms look similar to plants and animals that are alive today.
Importance of South African fossils
Did you know that South Africa is world famous when it comes to important fossil finds. South Africa has a very rich fossil record of plants, animals and early humans. Let's take a look at some of these.
Do you know of any important fossil findings in your area? If so, write it down below. If not, find out where the nearest fossil finding is to you and write it down.
Earliest life forms
Some of the most ancient fossils that are known to exist were found in rocks in Barberton area in Mpumalanga.
Do you know where this is in South Africa? Look it up on a map! These fossils are more than 3000 million years old! That is very, very old. They look like blue-green bacteria. Do you remember when we discussed microorganisms in the soil in Chapter 2? Bacteria are a kind of microorganism.
What do you know about bacteria so far? Go on a fact-finding adventure to see if you can find just two more facts about bacteria. Think about where you find bacteria, if they are good or bad for humans, and what they look like. Can you name any other kind of bacteria?
Learners can mention, for example, that bacteria make up a large group of microorganisms, and each is made up of only one cell. Bacteria are everywhere: in our food, in the soil, and even in our bodies. They are microscopic which means they are very small and you can only see the individual bacterial cells under a microscope. Some bacteria are helpful while some can cause disease.
Do you know where Grahamstown is in the Western Cape? Grahamstown is famous in the archaeological world for having some of the oldest and best preserved fossils of early plants from millions of years ago.
Look at the shape of Africa and South America on the classroom globe. The shapes could fit together like in this picture below. This diagram shows how scientists think the continents of Earth used to look millions and millions of years ago. This was called Pangaea.
A South African scientist thought that perhaps Africa and South America had been joined together long ago. But nobody knew if this was true.
Then scientists found fossils of a plant called Glossopteris in rocks in South Africa and they found fossils of the same plant in South America. This made more people think that perhaps Africa and South America were once joined, very long ago. The image below shows how scientists think the plant Glossopteris used to grow in the world, in the dark green.
Which number represents South America and which number represents Africa today?
The number 1 represents South America, and 2 represents Africa.
Do you think this fossil of Glossopteris leaves is a trace or body fossil? Explain your answer.
This is a body fossil as the leaf was covered in mud and then over time turned into a fossil. It is not an imprint, but the actual hard part of the plant has been preserved.
Fossils of dinosaurs have been found all over the world. But, one of the best places in the whole world is the sedimentary rock in the Drakensberg Mountains and the Maluti Mountains in southern Africa.
Where are the Drakensberg Mountains located in South Africa? Write down the provinces' names.
The Drakensberg are located mostly in Kwa-Zulu Natal and Mpumalanga.
Reptiles came before mammals. However, the fossil record shows us some animals which were similar to mammals as we know them today, but they were actually reptiles. They were in between! They are called therapsids. Fossils of these animals have been found in the Karoo in South Africa.
Fossils of some of the first mammals on Earth were also found in the Drakensberg rocks in the Eastern Cape and in Lesotho.
Where is the Karoo? A town in the Karoo is Graaff-Reinet. Find this town on the classroom globe. Find it on a map. Name some other towns found in the Karoo.
Somerset East, Willlowmore, Jansenville, Aberdeen
Astrange fish that lives in the sea near South Africa
Look at the picture below. This fish that was caught in the sea near East London. The fish is called a coelacanth.
Scientists from other countries rushed to South Africa to see this coelacanth fish. They could not believe that any coelacanths still lived in the sea. The scientists knew about coelacanths because they had studied their fossils in England and Germany, but the fossils were 80 million years old. The scientists thought that coelacanths had all died millions of years ago! We now call coelacanths "living fossils"!
How is this fish different from other fish? Look at its tail and its front fins.
The tail is thick and fleshy. Four of the fins have flesh and scales on them; they look almost like legs. Scientists who had studied the fossils wondered about these "legs". They wondered whether this fish was the ancestor of four-legged animals that live on land.
The Cradle of Humankind
The Cradle of Humankind is a World Heritage Site. It is called the "Cradle of Humankind" as many people and scientists now believe that this was where humans first evolved. The birthplace of humans is right in our country!
What does it mean if a place is a World Heritage Site? Find out and write your answer below.
It is a natural or man-made site, area, or structure recognised as being very important internationally and must therefore be protected.
The Cradle of Humankind is found in Maropeng just outside of Johannesburg in Gauteng. The name Maropeng, a Setswana word, means "return to place of origin".
In the Cradle Of Humankind about 1000 fossils of pre-humans have been discovered, dating back to millions of years!
Altogether there are 15 major fossil sites in the Cradle of Humankind. The Sterkfontein Caves is the most famous. Swartkrans and Bolt Farm are also sites at Cradle of Humankind where fossils have been found.
The fossils of `Mrs Ples' and `Little foot' were both discovered at Maropeng. Thousands of hominid fossils (hominids are human ancestors) as well as plants and animals have also been discovered there.
Tourists come from all over the world , including South Africa, to view the caves and fossils at the Cradle of Humankind and get immense knowledge on the history of humankind. If you live in or near Johannesburg, maybe you have been lucky enough to visit Maropeng and the Cradle of Humankind?!
Thinking about the Cradle of Humankind
Use the information above on the Cradle of Humankind to answer the questions below.
Why is the Cradle of Humankind famous?
Important fossils in the history of mankind have been found there.
Explain why you think it is called "The Cradle of Humankind".
This is because Maropeng is thought to be the birthplace of modern humans. Humans are thought to have evolved from Africa.
Give the names of two of the most famous hominid fossils that have been found at the Cradle of Humankind.
Mrs Ples and Little Foot
Explain why you think the fossils at Maropeng are protected by the country's law.
The fossils are very important as they help explain the evolution of humans, hence they have to be protected lest they be moved or destroyed.
- Sterkfontein Caves
- Cango Caves
- Bolts Farm
Answer: Cango Caves
What does Maropeng mean?
"Return to your place of origin"
As we have seen, there are many important fossil findings all over South Africa! Let's put all these places on a map in the next activity.
Plotting the important fossil sites in South Africa
- Identify all the places that have been mentioned in this Chapter which are important archaeological sites in South Africa
- Find these places on the map of South Africa and mark them in with an X and the name.
- Next to the place names, write down the important fossils which were found there.
- Animals and plants sometimes died in mud, and the mud kept their shape or preserved their remains.
- These remains of ancient plants and animals are called fossils.
- There are two main types of fossils - body and trace fossils.
- Fossils provide us with a record of the history of life on Earth.
- South Africa has a very important collection of fossils.
Are animal fossils made of bone? Explain what a fossil is.
A fossil is stone in the shape of the bone. Substances from rock have taken the place of each little part of the bone.
Which type of rocks are fossils normally found in?
Why do you think we only find fossils in this type of rock?
Sedimentary rocks can contain fossils because, unlike other rocks, they form at temperatures and pressures that do not destroy fossil remains. Dead organisms can become sediments which may ,over time, become sedimentary rock. Other rock types will destroy the fossils, such as magma.
Fossil wood does not burn. What is the reason?
Fossil wood is made of stone.
Some rock comes out of a volcano. It is red hot and then it cools and becomes hard. Can you find fossils in rock like this? Why?
No, because the red-hot rock would burn up any bone or plant that it fell on.
Name two fossils that show us the kinds of living things that lived long ago in South Africa.
Massospondylus, therapsids, Glossopteris, etc.
Explain how you think fossils can help us understand what life was like long ago on Earth.
Fossils give us a record of what life was like millions of years ago. We do not know what it was like as no one was there to write it down. So, fossils give us information such as what types of plants and animals lived long ago, how these organisms have changed over time, the effect of climate change on the Earth, we can even tell what animals ate from their fossils by studying their teeth and droppings.