Larry A. Stillman. age 13. of Milwaukee.
How did the prehistoric eras get named?
Not so long ago. people figured the world was about 6000 years old. Then Luis Agassiz got curious about glaciers. He saw how they skuffed and tore the ground among his native Swiss Alps.. He traced the footsteps of ancient glaciers over Europe and America. And so just over 100 years ago. mankind discovered the Ice Ages. The earth has kept a diary of her history written in rocks and recorded with fossils; Experts got down to read it. We now believe the old earth has had at least five billion birthdays.
Her diary falls into five long books called eras. The experts coined their names from older words. Each name tells how life was progressing in each era. The Archeozoic Era means the early beginning of life] It is written in Earths Diary. Book I and it lasted 650 million years.. No fossils are found from this era. But simple life forms may have helped make its limestone. graphite and iron. Much igneous fire‑formed rock was made at that time. These rocks were weathered and eroded in the quiet closing chapter of the era.
Then came the earlier‑life. the Proterozoic Era. It last 850 million years. Seas slopped over the land. Mud and debris settled to make slate and limestone. The rich iron ore of Lake Superior. certain gold' copper silver and cobalt deposits date from this era. And the oldest fossils are pressed in the rocky pages of this book. Simple algae and one‑celled creatures lived in those ancient seas. Book II closed with violent volcanic fireworks followed by a long period of quiet rest.
Book III is the Paleozoic Era. meaning old life. The busy era lasted 320 million years and its rocky pages teem with fossils. The gentle sea margins were friendly to living things. The shelled trilobites developed. then came fish and amphibians. And at long last the bare earth was invaded by plants and animals. In this era. the earth clothed herself with a green mantle of ferns and strange plants. Amphibians. reptiles. scorpions and dragonflies became tenants of the dry land. In the last chapter. continents are high and dry and the Appalachians are starting to grow.
The Mesozoic.. or middle‑lifer Era. covers 110 million years in Book IV. In it;. the giant reptiles were tested and failed. True birds took to the air and little mammals came to stays Cone trees developed and flowers came to embroider the green world. In the last chapter. the Rockies were beginning to poke up their noses.
The Cenozoic Era is still being recorded. This. era of recent‑life is but 60 million years old. In it. modern plants and animals took over the land. sea and air. The Ice Age glaciers dug valleys and lakes and smoothed plains to give the old earth a new face. When all. was ready. mankind arrived. Here at long last. was intelligence to use the beautiful. world. appreciate and enjoy it. Here at last was someone to read the diaries of earth’s long. long history.