The Second Presentation of the Time Line of Life
The first era is called the Paleozoic Era. Paleo means old and zoic means life. The Paleozoic is divided into 6 periods.: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. The Paleozoic Era is blue to represent life in the sea.
A. The Cambrian Period
This period is called the Cambrian period because the first fossils were found in Cambria, a part of Great Britain, now known as Wales. Later fossils of this period were found everywhere.
Everything that lived in this time lived in the water. Invite the child to identify as many animals as possible, at least by the phylum name: protozoa, porifera, coelenterates, worms, arthropods, mollusks, and echinoderms. All of these are invertebrates This is the beginning of the age of invertebrates. (In the child's work with the classification chart, she should have progressed up through arthropods.)
Look at the animals that are pictured all along the red line which is rising. These belong to the arthropods. Remember that arthropods means "jointed feet". Look at the characteristics of crustaceans,. These animals are called trilobites, and their bodies are divided into three parts. The trilobites were the most important animal of this period so it is called The Age of the Trilobite.
There were animals of different sizes and types in the ocean at this time. Some microscopic and some which were huge. The trilobites lived at the very bottom where there was no light and they were blind. They were plentiful, big and powerful. They were the most important animals because they had not predators - until the cold came. They could not change quickly enough when the seas became cold and part of it froze. They gradually became scarce and then disappeared altogether.
B. Ordovician Period
The name of this period comes from an ancient tribe of people known as the Ordovices who lived in a part of England where the first fossils of this period were found.
During this period, it is marked by the decline of the trilobites, but other animals appeared for the first time. Some looked like saws and were known as graptolites. They developed and increased in number, but for some reason they began to decline, too.
An echinoderm began to develop and reached its height and then declined.
Other animals were large cephalopods, starfish (echinoids) and scorpions. This is called the Age of Echinoderms because they were the most dominant animal of this time. One type of echinoderm was the most important of all: the SEA LILIES.
For a long time, people thought that the sea lilies were flowers or plants because they attached themselves to the floor of the ocean and formed large gardens. They seem to have a trunk and branch-like arms. Inside this trunk is the body of the animal, protected from its enemies by this trunk. They had long arms that waved in the current and a mouth at the center. When an animal passed by that he would like to eat, the sea lily would open its arms, wrap its arms around it tightly and pull the animal into its mouth. They always had food.
Some other animals that lived in this time were mollusks, cephalopods (kephale: head, podus: foot, headfoot) Large crabs, horseshoe crabs and starfish. All these animals consumed great amounts of calcium to make their shells, thus cleaning the water.
At the end of this period, there was a great swell of mountains.
C. Silurian Period
The Silurian Period was named after the Silures. They lived in a part of England where the first fossils of this period were found.
This period seems to be short, but it is very important. The sea lilies which were so huge in the Ordovician Period decline here and disappear. Animals were still needed to consume the calcium in the oceans, so the corals arrived. They ate lots of calcium and gradually built islands. Coral was very important. The corals began in the Silurian period. The line continues. They still exist today, but they are in danger of extinction.
During this period, we have the appearance of some very small protozoans, the Radiolaria and the first millipede.(look at the classification chart)
We've said that the Silurian Period was very important. If you look very carefully, you will see something very small. It is the first fish. The first creatures that have vertebral column. Theirs was not as hard as ours and was made of cartilage (show the child that their ears and nose are made of cartilage).
During this period some of the oceans started to dry up. Many algae found themselves dried by he sun on the shore. During this period, we see the first algae that attached itself to the mud and came up out of the water in search of a little sunlight. These were the first land plant, but plants without roots, stems and leaves. This plant had a small stem and tiny leaves, but no roots. It still had to put its feet in the water. These plants were the first mosses. (First there was algae living in the water, then mosses).
Why were plants the first living things to come out of the water? Because the air was full of Carbon Dioxide and the plants needed this. At this time, the earth still didn't have atmosphere. The atmosphere came about because the plants came out of the water. The plants used the CO2 and gave off oxygen. They were making life possible for animals on earth. Maria Montessori called this their "Cosmic Work". Everything in nature has this cosmic work. She describes this as things in nature doing something very selfish being unaware that they are also doing something that helps others.
At the end of this period is the second ice age. Under it we see the disappearance of the trilobites and the sea lilies (crinoids).
D. Devonian Period
The name Devonian comes from Devon in England where the first fossils of this period were found. The period coincides with he Age of the Fishes. The most import animals of this period are fish. Some of these first fish wore a kind of armor, perhaps to protect themselves. This line of armored fish only lasts in this period. The other types of fish continue and still exist today.
We also see the appearance of an insect very similar to the modern insects of today. Although many of the ancient insects have changed, this cockroach has not changed at all. It is the oldest insect we know. The cockroaches lived in the dampness of the swamps at about the same time as the dipnoids were breathing out of water. Millipedes lived in the water.
In this period the oceans receded and seas were formed between the different areas of land. Animals and plants remained in the muddy bottoms and had to learn how to live in the new surroundings. The algae grew longer and covered themselves with little leaves. Then the swamp lands began to dry up and the plants had to put down roots in order to hold themselves upright and to go in search of water.
F. Carboniferous Period
In this period, the animals start putting their heads out of the water. Remember, there is much more land near the water. First the plants came out of the water and purified the air. As the waters continue to recede, fish can be found in the marshes who breathed out of the water. They are called dipnoids and they still exist today., although there are very few. The name dipnoid means two kinds of respiration: one for when they are under water, gills, and one for when the swamp dries up and they must breath air, they use transformed swim bladders. It is believed that the dipnoids are a link between the fish and the amphibian.
During this period we have the appearance of amphibians, which means two lives. They are the first animals to live completely out of water, but they must stay in damp places. In this period, the amphibians developed to become the matters of land and water, therefore it is also called the age of Amphibians. There were many of them, and if they had enemies on land, they escaped into the water and vice versa. They laid their eggs in water in vast quantities because some would be eaten. During this period, the insects also developed. The dragonflies became enormous (18 inches across).
The name Carboniferous comes from the word carbon which is coal. This black strip is labeled coal for the coal in the earth which was formed in this time. The coal was formed by the development of land plants which still had no flowers or fruit. They made great forests. The trees like the animals started out very small and grew bigger each year trying to occupy all the space possible. They had enormous trunks with small leaves bunched at the top. These plants still exist today, but they are all very small: ferns, cycads, horsetails, etc.
This period is much longer than the preceding period. There were many revolutions in the seas. Sometimes the seas would rise and cover everything. Then the forest would become a swamp. This process went on for millions of years - each time burying the trees in their upright position. Slowly, over millions of years, theses trunks have been transformed into coal. Coal is nothing but wood that has become very old.
Look at the cosmic work of these plants. The trees didn't say, "We'll let the sea cover us so that we can produce coal" Like all other plants, and animals, too, the trees tried to occupy as much space as possible. This was their conscious work. However, we know that there is also their unconscious work. A great number of living things unconsciously prepare the world for those that come after them. The forests unconsciously purified the air by making oxygen and produced coal for those that came after them. "Those plants came back to life and live in our houses in the form of heat." Maria Montessori.
The brown strip under the black is labeled iron In the same way as there were little animals who fixed calcium in their houses to purify the oceans, there were at this time, protozoa who fixed iron in their exoskeletons, absorbing the iron from the water. During this period, a great number of rocks containing iron were formed made up of the remains of these animals. (Pure iron is hard to find as it is always mixed with other elements in rocks) These rocks containing iron were called ferrous. Thus this period has been named after the two layers: carbon (coal) ferous (iron) combined to make the name Carboniferous.
G. Permian Period
This is the last period of the Paleozoic Era. The name Permian comes from a part of Russia: a little town called Perm which is situated at the foot of the Ural Mountains where the first fossils of this period were found.
This was a very cold period as we can see by the symbol of the glaciers. The great big amphibians disappeared or returned to the water. Only smaller ones survived.
Something new appears in this period. It is very small. It is the first reptiles, the first animals who had learned to live completely on land. These animals were not afraid of the sun, as the amphibians were. Their bodies were covered by a thick skin that protected them from the sun. In fact, reptiles really like the sun, and they actually sunbathe. Instead of depositing their eggs in the water, the reptiles laid their eggs on land where the sun could warm them.
Immediately after their appearance, they became very big. The first big ones were herbivorous as there were so many plants to eat. Since they had no enemies, they soon became matters of the land. They multiplied and grew larger until they were truly giants.
There were many volcanoes and changes in the continents. Seas were cut off from the oceans, enclosed by land and they dried up. They left behind great salt deposits which were the beginnings of the deserts.
During this time, the first insects underwent metamorphosis. It was their way to overcome the cold. They were born in the spring and grew bigger during the summer. When the cold came, they enclosed themselves in a protection in which they spent their winter months. In the spring, they hatched out, looking different from before, but enabling them to travel, mate and lay eggs again.
By this time, there were many different plants and animals on the land and in the sea. The Paleozoic Era came to an end.
H. Mesozoic Era
The Mesozoic is the beginning of the age of reptiles. It is made up of three periods: the Triassic, the Jurassic, and the Cretaceous.
The Era is brown to symbolize the earth.
Reptiles that arrived during the Permian Period were found everywhere at this time in the water, in the air and on land. Some were carnivorous; others were still herbivorous. The reptiles had become very big, as big as houses, and they continued to be the lords of the earth.
They were strange-looking animals. These reptiles always had such very small heads on enormous bodies. The reptile had small brains in his tiny head, a spinal cord which extended the length of his great body, and at the end of his long tail was another little brain (actually a nerve ganglia). His body was so big that the tiny brain on his head could not take care of the end of his tail - so he had two.
We can tell that some of the reptiles were carnivorous by their terribly sharp teeth. Flying reptiles appeared. some had wings and also feather. These were called archaeopteryx. It is believed that birds descended from this reptile. Still others returned to the water, some taking the shape of fish.
Plants also progressed. For the first time, we have conifers, pines and fir trees. These plants still had no flowers, put they had pollen, which when blew in the wind to the female plant, producing eggs, or seeds.
During this point, we see the appearance of the first mammals, the monotremes (the platypus). These animals still lay eggs, but they nourish their young with milk.
The age of reptiles is very long and has been divided into three periods: Triassic, Jurassic, Cretaceous. The name Triassic means rock sediments that have been divided into three strata. Jurassic comes from the Jura mountains where the first fossils were found. Cretaceous come from a word meaning chalk because most fossils from this period were found in chalk deposits.
At the end of this age, plants had real flowers. The insects of which there were many at this time, fertilized the plants by carrying pollen on their wings as they flew from flower to flower drinking nectar, then dropping pollen onto the stamen of the female plant.
The earth was covered by ice at the end of this period. During this glacial period, all the great big reptiles disappeared. Some people think there was a great meteor shower during this period as well which changed the climate of the earth and made it impossible for the great reptiles to live.
Another animal existed during the time of the reptiles. It was small and was probably afraid to come out during the day. But it had warm blood and was able to sleep in the day and stay awake at night when the reptiles weren't around. This little animal was alert and perhaps clever and was able to survive the meteor or glacial period.
These little animals, the mammals, developed dramatically. Like all the other animals before them, they became numerous and occupied the most space they possibly could. They didn't remain only on the land. Some developed wings and few; some transformed their limbs and returned to the sea.
Bird were also developing. In the beginning, most of these animals were very different from the mammals as we know them. Gradually they changed and acquired the forms as they are familiar to us. We can compare this horse to the modern horse. Some other animals that are similar to the ones we know were fish, birds, amphibians and whales.
The age of Mammals is divided into four periods. All of the names have about the same meaning for all these contain "-cene", which comes from the Greek kainos, meaning new.
During this time, the only reptile survivors were crocodiles, lizards, snakes and turtles. Out of hiding places crept the mammals. During the Paleocene, they were small brained, large jawed, clumsy and inefficient. Some passed into extinction. This is when the hoofed mammals appeared.
Eocene means new. These descendants differed from the Paleocene. Lemurs and huge eyed tarsiers and the first monkeys made their appearance in Africa and S. America. Ancestors of the modern mammals such as the camel, horse and rhinoceros were during this time. They were very small: the camel was the size of a rabbit, the horse, the size of a fox, the rhino as big as a dog.
Oligocene means newer. These animals began to grow much bigger and take an important leap forward as in the whales, rhinoceros. The plant life took over cliffs and mountains, making a carpet of trees and grass.
Miocene means even newer. A creature called the Ramapithecus branched off from the ape line. This is one of the very primitive ancestors of modern humans.
and Pliocene means newest. The descendant Australopithecus became a human-ape, a border-line human being.
Throughout this Cenozoic Era, mammals were the dominant life force. Some of these animals developed grasping movements and binocular vision. Their babies were born dependent. Therefore, mammals gave their babies milk to nourish them during this era.
The red line is The Neozoic Era , the time of humanity and modern life.
We can see on the Time Line of Life that there were millions and millions of years of life on earth before humans appeared.
Control Of Error
Points Of Interest
This time line is a key - an impressionistic lesson.
Don't make it too complicated and don't be afraid to say "I don't know". The children will return to this for other lessons.
Have fossil specimens.
You can put animal specimens and class animals in evolutionary sequence under the time line.
Don't put up the time line until you are presenting it.
They have a strong interest in this work, so don't wait too long.
For all the presentations of the time line materials, the child matches all of the labels (names of eras and periods presented thus far) and the pictures pertinent to that period. The material may be left out, adding pictures to each new period as it is covered or the children may combine all of pictures of periods, presented and try to match to the right period.