The Clock of Eras: Introduction

Age
6-9.

Preparation
This chart tells the history of the Earth from the time it was a ball of flaming gas up to the present. We call it the Clock of Eras because it looks like a clock. This clock is special, though, because the colors tell a part of the story of our planet. This clock is different from most, though, for each hour on the Clock of Eras represents 250,000,000 years!

Presentation
A. Formative Era (Also called Azoic)

The first four hours are colored black. During this time, the Earth transformed itself from a mass of flaming gases into a planet with a cool, hard crust. The sun and earth were more alike then, but the sun did not cool like the earth. Its great size and heat brought about changes within our star, making light and heat stream out in all in all directions.

The Earth, much smaller, did not give off light. As it cooled, however, hot gases rose and fell on its surface. This was the cosmic dance. The rising flaming gas is represented by angels flying up with their basin of coals. When these gases were far enough away from the Earth they cooled. Then they descended, represented by angels flying down with their basins of ice. Slowly the crust was formed, but it was very thin. Inside, the earth still held flaming gases, which needed space to expand. Where weak spots in the crust broke open, the gases escaped and volcanoes were formed. The volcanoes we have today are very few compared to the number then. They threw out such ash and smoke that a thick cloud formed and the earth grew dark and colder. At some point, we don't know when, water was formed in these clouds and rain began to fall. At first this rain turned to steam and rose again, but there was so much water that it finally cooled the earth and stayed. The valleys and lower parts of the Earth were covered. Afterwards, the clouds thinned and the sun began to shine. On our Clock, we have now come to 4:00, and this long era is finished. How many years have passed? Even today, though the Earth's crust has thickened, it is still thin compared to the inside layers of our planet. There is still much heat and some of those layers are not solid. In cooling, the earth's crust formed huge plates, which rode upon the surface and rubbed against one another. Where they collided, great mountains arose and sank, earthquakes spread out, or volcanoes brought forth matter kept hot by pressure. This action continues today.

Humans have only seen the center of the earth with computer images. No hole has ever been drilled so deep. It is believed the center is formed of nickel and iron. The symbols for these elements are Ni and Fe. Some scientists have named the center of the Earth NIFE because of this. The layers around the center form the mantle. The crust, also called the lithosphere, is outside. Look closely on the chart and you will see the thin layer of water called the hydrosphere. Surrounding it, invisible but essential to life, is the atmosphere we breathe.

B. Paleozoic Era

The word Paleozoic comes from the Greek words Paleo, which means old and zoic, which means life. It is colored blue on the Clock of Eras to represent the color of the sea. This era lasted for approximately 385,000,000 years. This period saw the harmful ultra-violet rays of the sun beating down on the earth with no screen to protect it. Most life forms remained in the sea for protection from the sun. Now that the problem of putting more than one cell together was solved, more and more complex animals developed. During this period every phylum of the animal kingdom appeared.

C. Archaic Era

The word "Archaic" means "ancient". This time period is also called the Proterozoic Era. Proterozoic comes from the Greek Protero meaning early and zoic meaning life. It is colored yellow on the Clock of Eras to represent the fact that there was little life. At the beginning of this era the earth was five billion years old and still there was only one-celled life. Many one-celled animals developed in this era. This era is the period of great rains. The rains carried millions of tons of minerals into the oceans. Concentration of the minerals in the oceans caused the oceans to become poisonous. (Too much of anything can be very harmful) One-celled animals discovered how to take the poison in and make their shells. Foraminifera was the one-celled animal that removed the poisons from the ocean. The Forminifera did such a good job that their bodies cover about one third of our ocean floor.

D. Mesozoic Era

The word Mesozoic comes from the Greek, Meso meaning middle and, zoic meaning life. The Mesozoic Era is colored brown on the Clock of Eras because it represents land. This era lasted for approximately 150 million years. Great masses of land were emerging out of the water. In the Mesozoic Era an atmosphere developed. Animal life, which lived principally in the water, now began to live on the land. The atmosphere shielded the Earth from the ultra-violet rays of the sun. New and more complicated animals appeared on the land. The reptiles appeared and still exist. This is the age of the great dinosaurs.

E. Cenozoic Era

The word Cenozoic comes from the Greek word Ceno, meaning recent and zoic, meaning life. The Cenozoic Era is colored green on the Clock of Eras to represent the freshness of spring. This era lasted for approximately 65 million years. Two amazing things happened during this era: plants emerged on the land and animals developed that took care of their young. We know them today as mammals. Mammals bear their young alive and take care of them. The birds also played a major role at this time. Birds and mammals are the only warm-blooded animals. New volcanoes began to erupt. The climate grew a little drier and cooler and true flowering plants emerged.

F. Neozoic Era

The word Neozoic comes from the Greek word Neo, which means new and zoic, which means life. It is colored red on the Clock of Eras to signify the appearance of humans on Earth. The beginning of this era was characterized by the great Ice Age when glaciers appeared. In the beginning humans played a minor role. Later, humans lived in caves and discovered the use of fire. They made tools and weapons of stone and pieces of bone. They hunted wild animals for food and clothing. They painted pictures of these animals on the walls of caves.