Chapter 21 – Earth ’ s History

1. Chapter 21 – Earth’s History 21.1 – The Rock Record

2. Why study Earth’s history? • Scientists organize geologic time to help them communicate about Earth’s history.

3. Organizing Time • Fossils = the remains, traces, or imprints of ancient organisms. • By studying rock layers and the fossils within them, geologists can reconstruct aspects of Earth’s history and interpret ancient environments

4. Geologic Time Scale • A record of Earth’s history from its origin 4.6 billion years ago (bya) to the present. • The geologic time scale enables scientists to find relationships among the geological events, environmental conditions, and fossilized life-forms that are preserved in the rock record

5. http://geology.com/time/geologic-time-scale-550.gif

6. Visualizing Geologic Time • Eons = is the largest of these time units and encompasses the others • Divided into 4 different eons = Hadean, Archean, Proterozoic, and Phanerozoic • The three earliest eons make up 90 percent of geologic time, known together as the Precambrian. • During the Precambrian, Earth was formed and became hospitable to modern life. • Eons are further divided into eras

7. Eras • Usually tens to hundreds of millions of years in duration. • Divided into 4 different eras = Precambrian, Paleozoic, Mesozoic, Cenozoic • Eras are divided into periods

8. Periods • Tens of millions of years in duration • Each period in the geologic time scale contains epochs. • Epochs = hundreds of thousands to millions of years in duration

9. http://www.habitat.adfg.state.ak.us/geninfo/kbrr/coolkbayinfo/kbec_cd/html/image/figures/geotime.gifhttp://www.habitat.adfg.state.ak.us/geninfo/kbrr/coolkbayinfo/kbec_cd/html/image/figures/geotime.gif

10. In-Class Assignment/Homework • Your Geologic Time Scale

11. 21.1 – Notes Continued

12. Succession of Life-Forms • Phanerozoic Eon - multicellular life began to diversify • Paleozoic Era - the oceans became full of many different kinds of organisms http://www.palaeos.org/Paleozoic

13. Succession of Life-Forms • Trilobites = Small, segmented animals among the first hard-shelled life-forms. • They dominated the oceans in the early part of the Paleozoic Era. • Land plants appeared later, followed by land animals.

14. Succession of Life-Forms • End of the Paleozoic is marked by the largest mass extinction event in Earth’s history • In a mass extinction, many groups of organisms disappear from the rock record at about the same time • At the end of the Paleozoic, 90 percent of all marine organisms became extinct

15. Succession of Life-Forms • Mesozoic Era is known for the emergence of dinosaurs • Many other organisms appeared, including large predatory reptiles and corals in the oceans http://media-2.web.britannica.com/eb-media/50/8050-004-55077BBF.jpg

16. Succession of Life-Forms • During the Mesozoic, water-dwelling amphibians began adapting to terrestrial environments • Insects, some as large as birds, lived • Mammals evolved and began to diversify • Flowering plants and trees emerged

17. Succession of Life-Forms • End of the Mesozoic is marked by a large extinction event • Many groups of organisms became extinct, including the non-avian dinosaurs and large marine reptiles

18. Succession of Life-Forms • Cenozoic Era - mammals increased both in number and diversity • Human ancestors, the first primates, emerged in the epoch called the Paleocene, and modern humans appeared in the Pleistocene Epoch

20. In-Class Assignment/Homework • 21.1 WKT (Transparency & Study Guide)