Chapter 13 Interpreting Earths History Workbook p 277

Chapter 13 - Interpreting Earth’s History Workbook p. 277 -300

Detective Work • The Earth is 4. 6 Billion Years Old – See ESRT p. 8 and 9 • Earth was formed in the Big Bang – We will talk more about this in later chapters • Geologists use basic rules and clues in the crust in order to “unravel the mystery of our changing planet, its environments, and the development of life on Earth. ”

Telling Time Absolute Age • Actual Number • # • ie- I am 29 years old. You are 12 years old. This rock is 4 billion years old. Relative Age • Comparison • This vs. that • ie- You are younger than the Earth. I am older than you. You are younger than this building.

Rules of Geologists • Law of Uniformitarianism – – What does UNIFORM mean? The processes of today are the same as the ones of the past A rock that is placed in the river now will become ___ and ___. So, a rock that was placed in a river 100 million years ago will become ___ and ___. • Law of Superposition – What does SUPER and POSITION mean? – Newer layers are placed on top of older ones • Law of Horizontality – What does HORIZONTAL mean? – All layers will be placed down horizontally • Law of Relative Age – Layers are older than the processes that change them – So, if there are tilted layers, the layers were laid down horizontally and then something tilted them. Not the other way around.

Other Clues for Geologists • Intrusions and Extrusions – – – • Caused by Magma and Lava Which is in the Earth and which is out? You can tell the difference by Contact Metamorphism Do you remember what that is? See p. 279, Figure 13 -2 Crosscutting – The layer that goes through all other layers is the youngest • Folds and Faults – – • A fold is where 2 plates push together and fold the strata layer A fault is a break in the rock strata where movement occurred These can lead to exceptions to the Law of Superposition See p. 278, Figure 13 -1 Unconformity – Buried erosional surface – Does not show a complete geologic record • Index Fossils – Fossils are preserved remains or traces of ancient life • Body Fossils • Whole animal fossils- amber, frozen in ice, La Brea tar pits • Trace Fossils – Organisms that lived for a short period of time but over a large geographic area – What is a good example of an index fossil that is alive today? Something that covers the ENTIRE Earth, but has only been in existence for a short period of time?

What do geologists do with this information? • They establish a geologic sequence • Which came first? – Car or Road – Road or Rock – Fault or Erosion of Top – Fault or Layers – Top or Bottom

Practice

Open your workbooks to p. 280 1. 2. 3. 4. 5. 6. 7. D D D d

Geologic Time Scale Index Fossil • What is an index fossil? • What is a good index fossil alive today? Volcanic Ash Marker • Volcanic ash can work as an index fossil Ø These facts allow you to connect layers even if they are hundreds of miles apart

Geologic Time Scale • Most organisms that have lived on the Earth have become extinct • The atmosphere and oceans of the early Earth began to form with the gases emitted by volcanic eruptions • Early atmosphere was hostile and HOT • Where did the oxygen come from? • How much oxygen is there? Where would you find such information? !? • ESRT p. 8 -9 – Present is, where? Look at the millions of years! – Eon- most broad. There are only 2! • Most of the Earth’s “life” was spent in the ___. • Most things occurred in the ___. – – – – Era- subdivided Period- subdivided Epoch- most subdivided. Each Period has 2 or 3! Life on Earth Fossils Geology Landmasses

Geologic Time Scale • Evolution of Life – Simple to Complex – Most things aren’t alive today • Mass Extinctions – When a large group of organisms become extinct at once – Example? • Orogeny – Mountain Building

Geologic Time Scale • • • “Ceno-” means ___. “Meso-” means ___. “Paleo-” means ___. Most of Earth’s time was in the ___ eon. Most life evolved in the ___ eon. What is the most modern eon? Era? Period? Epoch?

Open your workbook to p. 155 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 3 4 2 1 2 3 4 3 2 3 4 4 2 1 3 34. 2 - Look at the Schist 35. 1 36. 2 37. 4 38. 1 39. 4 - The only one that makes sense 40. 2 41. 3 42. 2 43. 4 44. 2 45. 4 46. 4 47. 3 48. 4 49. 1 50. 2

Radioactive Decay • Geologists used to be able to only create a relative time scale • Then, they realized that certain chemicals, or isotopes, in nature will change, or decay, at a specific rate • This known, steady rate allows us to find the absolute age of rocks and fossils • This is called the half-life or radioactive decay

Types of Half-Life • ESRT p. 1 • Each isotope turns into something else in a set number of years • It doesn’t go away. It just changes. • The two that are the most used by geologists are Carbon-14 and Uranium-238 • C-14 has a ____ (long, short) half-life. • U-238 has a ____ (long, short) half-life. • In fact, how long is one ½ life of U-238? • How old is the Earth? • So, how many ½ lives has the U-238 gone through so far?

½ Life Table ½ Life 0 1 2 3 4 5 6 7 Years % C-14 % N-14 Fraction C-14 Fraction N-14

½ Life Table ½ Life 0 1 2 3 4 5 6 7 Years % C-14 % N-14 0 100 0 Fraction C-14 Fraction N-14 1 0

½ Life Table ½ Life 0 1 2 3 4 5 6 7 Years % C-14 % N-14 0 100 0 5700 50 50 Fraction C-14 Fraction N-14 1 1/2 0 1/2

½ Life Table ½ Life Years % C-14 % N-14 0 0 100 0 1 5700 50 50 2 11, 400 25 75 3 4 5 6 7 Fraction C-14 Fraction N-14 1 1/2 1/4 0 1/2 3/4

½ Life Table ½ Life Years % C-14 % N-14 0 0 100 0 1 5700 50 50 2 11, 400 25 75 3 17, 100 12. 5 87. 5 4 Fraction C-14 Fraction N-14 1 1/2 1/4 1/8 0 1/2 3/4 7/8 5 6 7 Now, you fill in the rest!