Unit 6: Interpreting Earth s History How do we know that the Earth has changed over time? Regent s Earth Science Name:
Topics Relative Dating Uniformitarianism Superposition Original Horizontality Igneous Intrusions, Extrusions and Inclusions Crosscutting concepts Folds and Faults Geologic Sequence of Events Geologic Time Scale (ESRT page 8 and 9) Geologic Maps (ESRT page 3) Evolution of Life (ESRT page 8 and 9) Mass Extinctions Index Fossils Geologic Time Markers Rock Correlations Radiometric Dating 2
Geologic History Earth formed BYA. (BYA = _) Or, Earth form MYA. (MYA = _) ESRT PAGE 8 & 9 The job of geologist is to. These clues come from fossils of animals, plants that provide information about. From the clues preserved in the rock record, scientists can determine the of the rocks. Geologist can date rocks two ways: Relative Dating (age) Absolute Dating (age) Key Concepts of Relative Dating: 1) Older = something that happened 2) Younger = something that happened 3) To find the relative are of rocks, you must examine or. a. Bedrock = rock underneath the surface b. Outcrop = bedrock exposed at the surface of earth 3
Principles of Relative Dating Uniformitarianism - the idea that the processes that shape Earth s surface today, such as,, and, are the same processes that occurred in. The present is the key to the past Principle of Original Horizontality Rocks are deposited in layers. - If the layers show any evidence of, or then those events are (happened after) than the formation of the rocks. (For example: If the rock layers are tilted, it happened AFTER the formation of the rock layer). Law of Superposition Rock layer on the bottom = Rock layer on the top = Overturned Layers Layers of rock that have been folded, and the layers are. The questions will say whether the rock layers have been overturned or not. (Most of the time, they have NOT been overturned). 4
Crosscutting Relationships Igneous Intrusions - = than the surrounding rock. Igneous Extrusions - = than the surrounding rock. **The rock is always than any type of deformation (eg. Folding, tilting, intrusion, extrusion)** Contact Metamorphism - temperature induced change of preexisting rocks along an intrusion - If the hairs touch the rock layer, then the rock layer is older than the intrusion (or the intrusion is younger than the rock layer). This is an because you have contact metamorphism on BOTH side. Let s review rocks formed from contact metamorphism!! This is an _ because you only have contact metamorphic underneath, or on one side. This shows a buried lava flow because there is a layer of shale on top. - Limestone turns into - Sandstone turns into - Shale turns into _. What rock would form at location A in the outcrops above? 5
Inclusions pieces of rock off and fall into rock. If the magma/lava is not hot enough to the rock, then the piece of rock is remain in the molten rock. The inclusion is than the surrounding magma/lava. Unconformity buried surface that shows a (or missing rock layers) in the geologic record. Formation of an unconformity: Deposition formation of rock layers. folding of rock layers (or tilting). Pushing rock above sea level. and of surface layers. Subsidence - of earth s layers followed by of new sedimentary layers. Unconformities are represented a squiggly black line. Let s draw in the uniformity. Look for where the rock layers have been cut off. What processes created the unconformity?? 6
Sequence of Events 1) Using the diagram below, place the following in order from oldest to youngest Youngest Oldest C B A 2) Using the diagram below, place the following in order from oldest to youngest Youngest Oldest C B A D 3) Using the diagram below, place the following in order from oldest to youngest. Be sure to include the tilting in the sequence of events. Youngest Oldest D C B A 4) Using the diagram below, place the following in order from oldest to youngest. Be sure to include the folding in the sequence of events. Youngest C Oldest A B 7
5) Using the diagram below, place the following in order from oldest to youngest. Be sure to include the faulting in the sequence of events. Youngest Oldest **Draw in arrows showing the movement along the fault. C B A 6) Using the diagram below, place the following in order from oldest to youngest Youngest Oldest 7) Using the diagram below, place the following in order from oldest to youngest. Be sure to include the tilting in the sequence of events. Youngest Oldest **Since the hairs of the contact metamorphism touch ALL the rock layers, it must be the ** 8
8) Using the diagram below, place the following in order from oldest to youngest. Youngest Oldest **The hairs only touch the layers below, so the layers ABOVE the intrusion must be ** 9) Using the diagram below, place the following in order from oldest to youngest. Line A - A represents a buried erosional surface (unconformity). Youngest A A Oldest 9
10) Using the diagram below, place the following in order from oldest to youngest. Line A - A represents a buried erosional surface (unconformity). Youngest Oldest 11) Using the diagram below, place the following in order from oldest to youngest. Line C - C and G - G represents a buried erosional surfaces (unconformities). Youngest Oldest 10
Geologic Time Scale - Earth s Formation began billion years ago. - This is a HUGE amount of time. To make it easier to talk about, and understand, Earth s history is up into different _ units called: o o o o Eons biggest unit of time ESRT PAGE 8 & 9 When one unit of time ends, and another begins it is because of _ such as the break up of. (older) = % of all Earth s history! o Broken up further into the Archean (oldest) and Proterozoic (youngest) - most of the chart makes up this Eon. Eras next largest unit of time o Begins with the Cambrian explosion! of life begins on earth. o Ends 251 MYA with a of trilobites. o Mammals and first appear on earth. o Ends 65.5 MYA with the mass extinction of ammonoids and many other land plants. = current geologic era. Periods most important unit of geologic time. (Many different periods). Cambrian = explosion of in life forms. Triassic = start of the Mesozoic era. Earliest and Quaternary = most recent period. First appear. Epochs smallest unit of geologic time. Pleistocene = the last. Early, Middle, Late used with the time. o o _ 11
Units of Geologic Time Practice For each of the following questions name the period during which the described event occurred. Event Description Epoch Period Era Eon 1. Earliest Fishes 2. Earliest Insects 3. Extensive coal-forming forests 4. Earliest Birds 5. Abundant grazing mammals 6. Salt and gypsum deposited in evaporate basins 7. Initial opening of the Atlantic Ocean 8. Life comes out of the oceans and onto land 9. The Adirondack region is uplifted 10. Most of North America is south of the Equator 11. Rifting and Initial opening of Iapetus Ocean 12. Pangaea begins to break up 13. Appearance of grasses 14. Earth s first forests 15. Mass extinction of many land and marine organisms (including trilobites) 12
The Evolution and Record of Life on Earth Earth s atmosphere 3 billion years ago, is very different from what it is today. Early Atmosphere Earth s early atmosphere was formed from. Early atmosphere missing. Earth was inhabited by organisms (do not use oxygen). How did Oxygen appear in the atmosphere? Organisms called created oxygen as a waste product. Oxygen was also produced by in the oceans. Enough oxygen was present in the atmosphere for aerobic organisms to evolve. Cambrian Explosion massive of organisms on the planet. Due to the appearance of in the Earth s atmosphere. Shale. Fossil evidence of the Cambrian Explosion can be found in the Evolution of Life as time goes on, species become more and. Most of the species that have every lived on the planet, have gone (no longer living). Charles Darwin survival of the fittest. Mass Extinctions - _ and decrease in the biodiversity on Earth. 1) Extinction of the Dinosaurs = _ MYA a. Impact Theory = Impact Crater found at _ b. The impact cause global change. The _ was blocked by the larger amounts of and. c. Evidence = thin layer covering the entire planet. 13
The Geologic History of New York State Refer to pages 8 and 9 of you reference tables to answer the following questions. 1. What are the three eras of the Phanerozoic Eon? a) b) c) 2. During which Epoch did humans first appear? About how many years ago was this? a) b) 3. What are the three periods of the Mesozoic Era? a) b) c) 4. During which three periods did dinosaurs live? a) b) c) 5. What two important geologic events took place during the Triassic Period? a) b) 6. About how many years ago did the first insects appear? a) 7. About how many years ago is the estimated origin of the Earth and Solar System? a) 8. How old are the oldest known rocks? From which Eon are they thought to be from? a) b) 9. During which period was the Acadian Orogeny? a) 10. How many years ago did the dinosaurs go extinct? a) 14
Geologic Time Markers Fossils Examples: bones, shells, footprints, and organic compounds (DNA) Fossils are only found in rocks. Index Fossils - fossil used to and geologic periods. TWO things make a good index fossil: 1. 2. Which letter would represent a good index fossil? Why? _ Volcanic Ash makes a great geologic marker. - Deposited over a area. - Deposits for a _ amount of _. 15
Index Fossils and Geologic History Practice 16
Alleghenian Orogeny? Orogeny = building event 17
Rock Correlation Correlation - _ What to look for when correlating rocks: Correlating based on Similarities in Rocks: Look at outcrops 1 and 2: OUTCROP 1 OUTCROP 2 1) Draw a dashed line from the top of the sandstone layer in outcrop 1 to the top of the sandstone layer in outcrop 2. 2) Which rock layer is the oldest? How do you know? 3) Which rock layer is the youngest? How do you know? Look at outcrops A and B: 1) Draw dashed lines to represent the missing rock between the two outcrops. 2) Which rock layer is the oldest? How do you know? 3) Which rock layer is the youngest? How do you know? OUTCROP A OUTCROP B
Look at outcrops I, II and III: 1) The rock layers in Outcrop II have been labeled for you. 2) Match the rock layers from Outcrop I, II and III. 3) Write the number in the boxes to represent the order of formation of the rock layers. 3 2 Identifying missing rock layers: Look at outcrop A and B: 1) What rock layer is missing in outcrop B? 2) Another name for a missing rock layer is an. 3) Draw in the symbol for a buried erosional surface. 3 1 Look at outcrops I and II: 1) Rock layer in Outcrop I has the same fossil as rock layer in Outcrop II. 2) Rock layer in Outcrop I has the same fossil as layer in Outcrop II. 3) The unconformity in Outcrop I represents missing rock layer from Outcrop II. 4) Rock layer is the youngest. 19
Look at Outcrops I and II. 1) Draw dashed lines to represent the missing rock between the two outcrops. 2) Which rock layer is missing in outcrop I? 3) Draw the symbol for an unconformity to represent this missing rock layer. 4) Which rock layer is the oldest? 5) In outcrop I, which geologic principle is best represented by the rock units? 6) In outcrop II, which geologic principle is best represented by the rock units? Using Volcanic Ash layers to correlate rocks: Look at outcrops A, B and C: A B C 1) What does the thick black line represent? 2) Match this layer in each outcrop. 3) Which layer is the oldest? 4) Which layer is the youngest? D E F 20
Using Index Fossils to Correlate Rocks 1. Write the time period of each rock layer based on the index fossils. a. Which rock layer is the youngest? i. How do you know? 1. 2. b. Which rock layer is the oldest? _ i. How do you know? 1. 2. 2. Using the index fossils, identify the age of each rock layer. a. Find the time period of formation for each index fossil. b. Which rock layers are the same age? c. Which rock layer is older, 3 or 7? d. Which is the youngest rock layer from both drill cores? 21
3. Using the index fossils, identify the age of each rock layer. a. Write the time period of formation in the boxes next to the index fossils. b. Draw in lines connecting the rock layers from Outcrop 1 and Outcrop 2. 4. Using the index fossils, determine the ages of the rock layers. a. What is the name of the index fossils in the oldest layer? i. During which time period did this organism live? b. What is the name of the index fossil in the youngest layer? i. During which time period did this organism live? 22
Absolute Dating Absolute Dating - using decay to determine the age of a,, or geologic events. Radioactive Decay - the of an over time Isotopes - of an element that have the same atomic number but differing atomic Examples: Stable carbon has a mass of 12 units called Carbon-12 Isotopic carbon has a mass of 14 units called Carbon-14 23
Half-Life - the required for of a _ product to to a product In a given sample of a radioactive isotope half of the atoms will decay to a stable product, but the remaining half is still radioactive Each element has its own half-life that range from fractions of a second to billions of years Unstable Isotope Decay Product Half-Life (Years) Half-Life (Years) Carbon-14 5.7 x 10 3 Potassium-40 1.3 x 10 9 Uranium-238 4.5 x 10 9 Rubidium-87 4.9 x 10 10 The half-life of an isotope is not effected by any environmental factors such as _, _, or chemical reactions Compared to the half-life of the material in figure A, the half-life of the material in each small cube in figure B is. 24
Radioactive Isotopes Uranium-238 - the most important isotopes when dating rocks or events millions of years ago Examples of dating with Uranium-238: o o Decay: Uranium-238 Half-Life: _ Carbon-14 - one of the most important isotopes when dating remains within tens of thousands of years Examples of Organisms dated with Carbon-14: o o o o Decay: Carbon-14 Half-Life: Carbon-14 Nitrogen-14 % Carbon-14 % Nitrogen-14 Mass Half-Life Years Material Material Carbon-14 + 1 + 5,700 2 100 - % C-14 2 Mass Nitrogen-14 Image 0 1 2 3 4 25
1. Complete the following table showing the percent remaining of original Carbon-14. a. After 22,800 years, approximately what percentage of the original carbon-14 remains? 2. Complete the following table showing the remaining grams of original Carbon-14. a. After how many years will 0.008 grams of the original Carbon-14 remain? 0.50 0.25 0.125 3. Shade in the amount of stable material present in the material after it has undergone a second half life period on the diagram below. a. If this radioactive element is Uranium, how many years have elapsed? 26