2. Geologic Time

3. Part 1 - Dating Earth Materials A.Absolute Dating 1.Finding the ACTUAL age of materials and events; # of years B.Relative Dating 1.Comparing the times when events occurred 2.Making a list of oldest to youngest

4. Example Relative Age (sequence) Absolute Age (years) End of last Ice Age US becomes independent Dinosaurs become extinct This school is built People first land on the moon First insects appear on Earth Your birth First Human beings appear Columbus discovers America 518 5 1 million3 15-179 408 million1 428 447 60 million2 2346 10,0004

5. A. Absolute Dating A.Radioactive Decay 1.Certain materials (radioactive) give off particles at a steady rate 2.Rate of Decay is NOT affected by temp, pressure or breakage of material

6. Absolute Dating 3.Half Life a.Amount of time it takes for half of the radioactive material to decay (change to another element) Parent to Daughter element b.Carbon 14 = C 14 to N 14, half life 5,700 years c.Example 1)After 5,700 years (5.7 x 10 3 ), 100g of C 14 will turn into 50g of C 14 and 50g of N 14

7. Absolute Dating # Years# Half Lives # Heads# TailsFraction of Heads Percent of Heads 004000400/400100 % 31 62 93 124 Magic Coins: Every 3 years, half of the heads change to tails. Half life is 3 years.

8. Absolute Dating d.Carbon-14 can ONLY be used if substance: 1)Was organic 2)Is less than 50,000 years old e.Uranium-238 1)U 238 to Pb 206 2)Half Life = 4.5 x 10 9 years f.Potassium-40 1)K 40 to Ar 40 2)Half Life = 1.3 x 10 9 years 3)Most often used to date materials too old for C 14

9. Absolute Dating

10. B. Relative Dating A.Index Fossils 1.Remains of plants or animals that lived for SHORT time over a LARGE area (small vertical, large horizontal) B.Principle of Uniformitarianism 1.All processes that occur now ALSO occurred in the past

11. Relative Dating C.Law of Superposition 1.In sedimentary rocks the youngest rocks are at the top and the oldest are at the bottom 2.Exceptions a.Folding over of layers (overturning) b.Sliding along a fault

12. Relative Dating 1)Which layers are the same? 2)Which layers are the oldest / youngest? 3)What does the wavy line mean?

13. Relative Dating D.Extrusions 1.Formed when molten rock flows onto the surface and hardens E.Intrusions 1.Formed when molten rock forces its way into rock layers and hardens without reaching the surface F.Extrusions and Intrusions are YOUNGER than the surrounding layers IF there is contact metamorphism

14. Relative Dating G.Faults 1.Breaks in rock where movement has taken place 2.Rock is OLDER than ANY fault it contains H.Unconformity 1.Former surface that was eroded and buried

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16. Relative Dating I.Volcanic Ash Deposits 1.Excellent time markers 2.RAPIDLY deposited over a LARGE area

17. Part 2 - Interpreting Geologic Events Order the events from oldest to youngest

18. Correlation of Rock Layers A.Methods 1.Lithology a.Matching layers by comparing rock type, composition and texture 2.Index Fossils a.Compare fossils within layers b.BEST method