2014 Mrs. Hughes 8th Grade Science Geologic Time Shows Earth’s History

Uniformitarianism Earth is an always changing place The same forces of change at work today were at work in the past The Earth has changed gradually (very slow)

The Geologic Time Scale Shows Earth’s History divided into time units based on life forms that existed and major events.

Earth is estimated to be 4.6 billion years old. Oldest living things were one-celled organisms at about 3.5 billion years. Humans show up only about 100,000 years ago.

Division of Geologic Time Eons – largest unit Eras – eons are divided into eras Paleozoic, Mesozoic, Cenozoic Periods – eras are divided into periods Epochs – periods are divided into epochs

Precambrian Time The longest part of Earth’s history About 4.5 billion years. 1st rocks formed 3.9 billions years ago. 1st living things appear about 3.5 billion years ago during the Precambrian; single-celled simple organisms (bacteria) .

Precambrian Time Invertebrate (no backbone) animals show up at the end of the Precambrian. This time ended with a global ice age.

Paleozoic Era 544 mya – 248 mya Means “ancient life” often known as the age of fish. At the beginning of this era there is an explosion of life in the warm, shallow seas of the time. Organisms with shells and vertebrates (backbone) form. Trilobites, mollusks, fish, amphibians

Paleozoic Era Life moves onto land at the end of this era and the first reptiles and large insects form. Appalachian mountains form. Pangaea forms. .

Paleozioc Era Largest mass extinction marks the end of this era. 95% of all life disappears in the fossil record One theory is global – climate change due to massive volcanoes

Mesozoic Era 248 mya – 65 mya Means “middle life” and often know as the age of reptiles. Dinosaurs ruled the Earth First flowering plants First birds and mammals Pangaea separates

Mesozoic Era Another mass extinction at the end of this era. Most excepted theory is a massive asteroid hit the Earth causing global-climate change.

Cenozoic Era 65 mya - present Means “recent life” and known as the age of mammals Several ice ages Fossils of the 1st humans show up 100,000 years ago. (not very long ago in geologic time)

Quick Check 1. ____ is the idea that the forces that changes the Earth today are the same forces that existed in the past. A. Paleontology B. Uniformitarianism C. Cambrianism D. Geology

Quick Check 2. ____ are the oldest living things thought to have first formed 3.5 billion years ago. A. Mammals B. Birds C. Trilobites D. Bacteria

Quick Check 3. ____ is the era dominated by life in the oceans. A. Precambrian B. Paleozoic C. Mesozoic D. Cenozoic

Quick Check 4. At the end of the ____ era, an asteroid hit the Earth causing mass extinction and the end of the dinosaurs. A. Precambrian B. Paleozoic C. Mesozoic D. Cenozoic

Quick Check 5. Which picture shows a close representation of the geologic time scale? A. B. C. precambrian paleozoic mesozoic cenozoic paleozoic mesozoic cenozoic precambrian cenozoic paleozoic precambrian mesozoic