Geologic Time

1. Geologic Time P. Lobosco

2. The Geologic Time Scale • Earth’s history on the geologic time scale is divided into four geologic eras: Precambrian Era, Paleozoic Era, Mesozoic Era and Cenozoic Era. Eras are broken down into smaller divisions called periods. The Earth formed 4.6 billion years ago.

3. Precambrian Era • The Precambrian Era is the longest era. It lasted about 4 billion years or 87% of the Earth’s history. Life exists only in the sea.

4. Life in the Precambrian Era • Just beneath the seas surface there bacteria clumped together in a tangled mat of threadlike fibers. Plants related to modern seaweed are also in the seas. They use chemical’s from the water and energy from the sun to make their own food. In the process they produce oxygen. By the end of the Precambrian Era, animals such as jellyfish, worms, corals and sponges have appeared in the seas.

5. Paleozoic Era • The Paleozoic Era lasted about 345 million years. In the Paleozoic Era, life comes ashore.

6. Life in the Paleozoic Era • Life is abundant in the seas, including trilobites, brachiopods, and fish. The land is no longer lifeless. Forests of ferns and cycads grow. Amphibians now appear. Late in the period reptiles appear.

7. Trilobite • The trilobite is an important index fossil for this era since they both evolve and become extinct in this era. They have large heads, thorny spines and body divisions.

8. Brachiopods • Parts of the ocean floor contain lampshade- shaped shells. The shells have two parts that close to cover and protect the soft animal within. These animals are brachiopods.

9. Fish • Fish are the first vertebrates, or animals with backbones. The Devonian Period is often called the Age of the Fishes.

10. Life on Land in the Paleozoic Era • Life on land now includes forests of ferns and cycads. Amphibians appear. By the end of the Paleozoic Era the Amphibians are reduced and new animals, reptiles appear on land.

11. Amphibians • Amphibians, such as Eryops, are the first land vertebrates. They spend their early lives in water and move to land. Eryops is much larger than the frogs and toads of the 20th century. It is 2 meters long with a large head and a thick clumsy body. It searches the forest for king-sized roaches. It must keep its skin moist so it cannot move far from water.

12. Reptiles • By the end of the era, amphibians have been reduced since there is a drought and the climate has cooled. Mountains are rising and all the landmasses are joined together. The reptiles appear. Their tough skin is protected by scales or plates. Unlike amphibians, they do not lose water through their skins. Their eggs have thick shells so they do not dry out.

13. Mesozoic Era • The Mesozoic Era lasted about 160 million years. The Mesozoic Era is a period of many changes. Pangaea begins to break apart. The expansion along the ocean floor causes the continents to gradually spread apart. Mountain ranges, such as he Sierra Nevadas and the Rockies were formed. The Mesozoic is divided into three periods, Triassic, Jurassic and Cretaceous.

14. The Triassic Period • The drought that began in the Paleozoic Era has not ended. It is even hotter. North and South America have begun to separate from Africa. A narrow sea forms that will become the North Atlantic Ocean. Sea creatures that are reptiles, have fingerlike projections, and lungs have returned to the sea. Mammals appear. The first dinosaurs appear.

15. The Jurassic Period • The Age of Dinosaurs has begun. Volcanoes are active in the American West. The mountains of the Sierra Nevada and the Rockies are still rising. The southern continents are beginning to separate. Conifers make up the forest. The first bird, Archaeopteryx, appears.

16. The Cretaceous Period • The Cretaceous Period is a time of flooding of the continents. The continents continue to move apart. By the end of the period the continents are almost in their present condition except North America and Europe are still joined. Dinosaurs rule the world but by the end of the period all of the dinosaurs and sea living reptiles will have died. Sea levels drop and rivers dry up. • Flowering plants appear.

17. Cenozoic Era • The Cenozoic Era, our present era, has only lasted about 65 million years. The Cenozoic Era is divided into two periods, the Tertiary Period and the Quaternary Period. Great sheets of ice will sweep across the land.

18. The Tertiary Period • The Uintatherium was one of the largest mammals ever. It existed with the ancestor to the rhinoceros. The first humanlike creatures begin to walk upright on the African Plains. The remains of a small adult female from this period, about 1 meter tall, is discovered in 1977. She is named “Lucy”.

19. The Quaternary Period • The climate turns sharply colder. Four ice ages occur. Large parts of Europe, North America and South America are covered in sheets of ice. The Ice age ends about 11,000 years ago. AS the world warms, farming becomes widespread and modern civilization begins.

20. Evolution • The world evolution comes from Latin and means an unfolding or opening out. A scientific translation is descent with modification. Evolution can be defined as a change in a species over time. A species is a group of organisms that share similar characteristics and that can interbreed with one another to produce fertile offspring.

21. Mutations • A change in a gene will produce a change in the offspring of an organisms. A change in a gene is called a mutation. Usually a mutation produces an organism that cannot survive. A change that increase the chance of survival is called an adaptation. The development of a new species can result in the extinction of another.

22. The Fossil Record • The fossil record indicates that species have evolved over time. For example, the discovery of the skull of a mammal similar to a whale in 1983 with a structure for hearing that could not have worked underwater led scientists to infer that at one point the whale lived on land.

23. Mass Extinction • During 1640 and 1859 species began to disappear at the rate of one every five years. Between 1850 and 1900 the rate increased to one lost every nine months. At the current rate scientists estimate that 1/5 of the species in the rainforest will be gone in 50 years.