1. CHAPTER 6C EVIDENCE OF THE PAST

2. Paul Sereno……1995 Found dinosaur skull 1.5 m long Paleontologist – use fossils to reconstruct the past

3. Fossils Trace remains or imprints of living organisms that are preserved by geological processes.

4. The Age of Fossils Relative Dating – estimating the age of rocks or fossils by their depth in sedimentary rock Absolute Dating – measuring the time it takes for an unstable atom to decay

5. Absolute Dating

6. The Geologic Time Scale

7. Mass Extinctions When a species dies out Scientists feel that the dinosaurs died out so quickly because of a fast changing environment

8. The Changing Earth

9. Precambrian Time Grand Canyon Bottom 4.6 billion yrs -----  542 million yrs Life began here Atmosphere was CHAOTIC NO Oxygen early on 1 st prokaryotes

10. Precambrian Time 2 nd – Cyanobacteria Photosynthesis and oxygen --  ozone NOW life on earth surface 1 billion yrs ago Multicellular organisms eukaryotes

11. Paleozoic Era 542 million --  251 million WATER – sponges, corals, snails, squids, trilobites, fish, sharks LAND – ferns, mosses, horsetails, conifers NO flowering plants Insects Salamander-like animals

12. Paleozoic Era END of REPTILES and winged insects MASS EXTINCTION – 90% of water species are gone

13. Mesozoic Time 251 million – 185.5 million “Middle Life” Age of Reptiles –Dinosaurs –Birds –Conifers –Flowering Plants

14. Mesozoic Time EXTINCTION ??????????

15. Cenozoic Time 65 million – today Recent Life Age of Mammals –Mastodons –Saber toothed cats –Camels, sloths, small horses –Humans

16. Cenozoic Time ICE AGE Organisms moved to Equator to live or become extinct