1. The Geologic Time Scale A History of Earth and Life

2. Geologic Time Scale Division of Earth’s history into blocks of time

3. Ideas about time… Processes & Forces that are occurring now occurred in Earth’s past But how do we tell how old things are…

4. 1. Relative Dating Trying to determine which rock units formed first, second, third, & so on… Forming a sequence of time…no dates!

5. Rules for Relative Dating 1. Rocks on the bottom are older than rocks on top Law of Superposition

6. 2. Principle of Original Horizontality Layers of rock are generally deposited in a horizontal positions

7. 3. Rock that cuts through is younger than the rock it cuts Principle of Cross-Cutting

8. Matching Rock Layers Correlation To make a time scale we have to be able to find similar rock in different areas

9. Fossils also help… What are fossils? Remains or traces of an organism that have been preserved

10. Types of fossils 1. MOLD – created when an organism is buried in sediments & is dissolved by underground water

11. Types of fossils 2. CAST – Created when the hollow spaces of a mold are filled with mineral matter

12. Types of fossils 3. CARBONIZATION – occurs when an organism is buried under fine sediment. Pressure causes only a thin residue of carbon to be left. Best for preserving leaves & delicate animals

13. Types of fossils 4. Impression – a replica of the surface that occurs when the carbon film is lost.

14. 5. Amber – Created when organisms are preserved in tree sap (resin) Types of fossils

15. 6. Petrified – Occurs when minerals from water replace the organism “turned to stone”

16. 2. Absolute Dating Radiometric Dating & Radiocarbon Dating Radioactive decay is used to date fossils. This gives us a specific time that the organism died.

17. So lets look at what this showed us…

18. Earth is about 4.6 billon years old

19. Pre-Cambrian Era 4.6-540 mya 3.6 bya life appears - Single celled organisms First prokaryotes (bacteria)

20. Paleozoic Era (Cambrian Period) 540 mya Explosion of multi-cellular life in oceans

21. Paleozoic Era (Ordovician Period) 490 mya Many new invertebrates in seas; first land plants

22. Paleozoic Era (Silurian Period) 443 mya Fish dominant; first insect fossils; land plants diversify

23. Paleozoic Era (Devonian Period) 417 mya Fish dominate seas; First amphibians

24. Paleozoic Era (Carboniferous Period) 354 mya Amphibians and insects dominate land; first reptiles

25. Paleozoic Era (Permian Period) 290 mya Mammal -like reptiles

26. Mass Extinction 248 mya 95% Marine species extinct; 70% land species extinct

27. Mesozoic Era (Triassic Period) 248 mya Small reptiles and mammals; First dinosaurs

28. Mesozoic Era (Jurassic Period) 206 mya Dinosaurs dominant; first birds appear

29. Mesozoic Era (Cretaceous Period) 144 mya Dinosaurs dominate; first flowering plants

30. Mass Extinction 65 mya 85% of all species extinct

31. Cenozoic Era (Tertiary Period) 65 mya Mammals and birds dominate

32. Cenozoic Era (Quaternary Period) 1.8 mya - today Mammals abundant; Humans appear == holla ==

33. You know the history of life!