Regents Earth Science Unit 12: Geologic History Earth s History

Transcription

1 Fossil - the remains or evidence of a living thing Regents Earth Science Unit 12: Geologic History Earth s History only hard parts fossilize found in sedimentary rock Official NYS fossil: Eurypterid Fossils can form in the following ways: Petrification replacing living tissue with minerals Preserved Fossils frozen or amber Types of Fossils Casts and Molds imprints of tracks, etc. Drying mummies Others Fossil Formation: 1. Organism dies 2. soft parts decay or are eaten 3. hard parts are buried in sediment 4. sediment becomes rock 5. uplift, weathering and erosion expose the fossil Fossils

2 Fossils Indicate Four Factors in Earth s History: 1. life changed/evolved over time 2. Earth's surface has changed marine fossils are found at high elevation 3. Earth's climate has changed tropical coral fossils are found today in NYS 4. appearance and activity of past life teeth give clues to what an animal ate bones give clues to how the animal looked and move Two Processes help us determine the age of earth s rocks and events: Relative Dating determining if something is older or younger Absolute Dating (Radioactive Dating) determining an approximate age in years Fossils Earth s History Relative Age - the age of something compared to something else Geologic Column - an ideal sequence of rock layers created by combining data from all known rock sequences at various locations Relative Dating

3 Rules of Relative Dating: Relative Dating youngest Law of Uniformitarianism - processes that change Earth today are the same as those that changed it in the past "The Present is the Key to the Past" Principle of Original Horizontality - sedimentary rocks form in horizontal layers (sedimentary rocks not in horizontal layers have been changed since they formed) Principle of Superposition - in any undisturbed sequence of rocks, the oldest rocks are at the bottom, youngest at the top Rocks are older than the events that happen to them (because the rocks exist first) oldest Tilting, Folding, Faulting, and Intrusions are all younger than the rocks they effect Tilting Folding Faulting Intrusion Unconformity - buried erosional surface, represents a gap in time in Earth's history Formation of an Unconformity:

4 relagecycle.gif (29947 bytes) Sequence of Events putting events in order of age from what happened first to what happened last Sequence of Events: 1. deposition of limestone 2. deposition of sandstone 3. deposition of shale 4. deposition of limestone 5. deposition of sandstone 6. faulting of rock layers 7. intrusion of igneous rock Relative Dating Sequence of Events Sequence of Events that formed the landscape cross-section at the left: 1. Deposition of layers Intrusion of #6 3. Tilting of layers 1-5 and Intrusion of #6 4. Erosion of rocks 5. Deposition of layers 9,10 6. Erosion of rock layers

5 Relative Dating - Correlation Correlation matching rock layers from around the world Index Fossil - a fossil of an organism that lived for a short, well defined period of time and lived over a large geographic area used to date the rock layers in which it is found index fossil Index Fossils:

6 Relative Dating Correlation Index Fossils of New York State are found at the bottom of the Reference Tables p. 8-9 the letter on the index fossil at the top of the page is located on the time lines at the center of your chart where the letter is located is the time when that fossil existed the length of the line represents the entire time that any fossils of that animal species may have existed

7 Relative Dating Correlation Volcanic Ash - can also act as an index to correlate rocks of different regions ash blown high into the atmosphere encircles the Earth and settles world wide as a thin layer of sediment this sediment lithify and become a thin layer of sedimentary rock Absolute Dating Radioactive Dating - method used to determine the absolute (actual) age of a rock or event certain elements spontaneously decay (change) into different elements radioactive (parent) element - has an unstable nucleus that decays decay (daughter) element - stable element that is the result of radioactive decay Reference Tables p. 1 Half-Life - the time it takes for one-half of a radioactive element to change into a decay element the rate of decay is NOT effected by: 1. heat 2. pressure 3. chemical action Radioactive Decay Graph: % Element

8 Absolute Dating Potassium-40 is used to date rocks/events millions to billions of years old Uranium-238 rarely used - uranium not found in most rocks Carbon-14 is used to date rocks/events up to ~50,000 years old radioactive decay is accurate for dating up to 5-7 half-lives: Carbon 14 (half-life = 5,700 yrs.) Geologic Time the Geologic Time scale divides Earth's history into sections of time (from largest to smallest): 1. Eon 2. Era 3. Period 4. Epoch boundaries between time periods represent changes in the life on Earth due to evolution and mass extinctions Earth formed 4.6 billion years ago Reference Tables p.8-9

9 Geologic Time Reference Tables p. 8-9 the time scale is divided into units of time called Eons Eons are subdivided into Eras Eras are subdivided into Periods Periods are subdivided into Epochs the absolute ages of the rocks for each time period are listed

10 Geologic Time Reference Tables p. 8-9 the life that existed on Earth is listed when they lived on Earth when major life-forms became extinct is also listed

11 Geologic Time Reference Tables p. 8-9 the bedrock that existed in NYS is shown by a dark line ex.: NYS has a complete rock record of rocks from the Cambrian to Devonian

12 Geologic Time Reference Tables p. 8-9 the major geologic events in NYS and what the landmasses of Earth looked like are given at their proper time in Earth s history