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  1. 1. Earth Science Earth’s History Notes I. Introduction a. As we already learned the earth is always changing b. The history of the earth is told by _________________ ___________________________________________ c. It is up to the scientist to figure out the puzzle of these geological events. II. Early Earth a. There is evidence that states that the atmosphere and the oceans of the early earth ___________________________ _______________________ _________________________ _________________________ _________________________ b. There were large amounts of i. ____________________ ii. ____________________ iii. _____________________ iv. _____________________ That came out of the earth from a process called ___________ v. The vapor was ________________________________ ___________________________________________ c. The early earth was also covered by clouds that formed precipitation over millions of years that cooled down the hot surface of the earth and also formed oceans. d. What is the proof to this? i. _________________________________ __________________________________ __________________________________ e. Today’s atmosphere is made up of 21% oxygen but the gases of eth volcanic eruptions do not contain oxygen i. SO WHERE DID WE GET THE OXYGEN FROM? 1. ______________________________________ ______________________________________ ______________________________________ -1-
  2. 2. Earth Science Earth’s History Notes a. Photosynthesis produces extra oxygen that went into the atmosphere over millions of years. III. Sequence of Geological events i. Knowing the sequence of events that took place during the formation of the earth’s crust helps us develop a history of the earth to better understand the earth ii. Relative age is _______________________________ __________________________________________ 1. As shown in the appearance of the rock layers 2. Relative age is not really concerned with the age of the rocks ______________________________ ______________________________________ 3. This method uses a. sedimentary rock layers b. igneous extrusions and intrusions c. faults d. folds e. continuity f. similarities of rock g. fossil evidence h. and volcanic time markers As clues to determine what was the probable sequence of events iii. The actual age of a rock or a fossil is called __________ 1. The best way and more precise ____________ ___________________________________ ___________________________________ 2. EVERY RADIOACTIVE ELEMENT DECAYS 3. How does this work? a. _______________________________ _________________________________ _________________________ b. Sometimes this changing process goes through steps c. -2-
  3. 3. Earth Science Earth’s History Notes d. We also know how _________________ _______________________________ e. We use a process of half life. Since we know how long the half life ( time takes ½ the isotope to decay) is ______________ _________________________________ _________________________________ b. Chronology of layers i. The law of superposition 1. ________________ ________________ ________________ ________________ a. This is used to determine the sequence _______ _________________________________ b. This works as long as the group was not overturned not had an older rock put over it c. Igneous Intrusions and Extrusions i. Igneous Intrusions 1. formed when magma is injected into older rock layers in the crust 2. younger than rock they are found in 3. look for contact metamorphic rock in layer above and below the intrusion ii. Igneous Extrusions 1. rocks that ______________ ______________________ 2. younger than rock layers below 3. ______________________ ______________________ iii. Why do we look at the metamorphic rock near these two rock formations? 1. The reason is contact metamorphism – (the rock forming due to the contact of lava) ________________________________ -3-
  4. 4. Earth Science Earth’s History Notes d. Faults Joints & Folds i. Folds 1. bends ______________ 2. occur ______________ ___________________ ii. Faults 1. cracks in rock layers where some movement has taken place 2. Faults produce offset layers. iii. Joints 1. _________________________ iv. These three rock layer characteristics occur _________ ___________________________________________ ___________________________________________ v. These three rock characteristics are also ___________ ___________________________________________ 1. Since the rocks that fold, faults or joints are there before ________________ e. Internal Characteristics i. Fragments that occur in a rock as we can understand are older than __________________________________ ________________________________ ii. Cracks and veins in a _________________ _________________________________ iii. Veins – are mineral ____________________________ _________________________________________ iv. Sedimentary rocks are ________________________ __________________________________________. v. Unconformity 1. Is the ________________________________ 2. They are found between two ages of rock levels 3. Usually these ______________________ ___________________________________ 4. It looks like a buried Erosional surface -4-
  5. 5. Earth Science Earth’s History Notes 5. ________________________ ________________________ ______________________________________ ______________________________________ IV. Relative Age a. We use different correlating techniques to find out how old a rock really is b. You have to be careful though to use facts and not inferences when figuring out this information i. Correlation is the act of matching rocks of similar age in different places 1. This is best done when rocks are not covered in dirt and plants 2. This can be so easy by identifying a certain mineral type, color and then searching for it in different places ii. one technique is called INDEX FOSSILS a. this is using the remains of animals that are known to have lived and died in a certain time period b. If we find one ____________ ____________ ____________ ____________ ____________ c. We also use Index fossils to decipher rock records i. Organism ___________________________ ____________________________ ____________________________ d. How does a fossil fit the index profile i. Easily recognizable -5-
  6. 6. Earth Science Earth’s History Notes ii. _______________ iii. ________________ ________________ iv. _______________ ___________________________ iii. Volcanic Time Marker 1. When a volcano ________________________ ____________________________________ ____________________________________ 2. This may be a time marker if we find a layer of ash in the layers ___________ ______________________________ ______________________________ 3. This time marker will be very helpful determined the ages of rocks below and above it iv. Problems with Correlation 1. It _________________________________ ______________________________________ _____________________________________ 2. However, it can lead to misinformation a. With very careful study of 2 like rock formation they might still be different ages. b. ________________________________ ________________________________ V. Geological Times a. Rock Record i. As we just learned that scientist use index fossils (guide fossils ) to tell how old a rock is. ii. Scale of geological time 1. scientists have organized the geological time scale a. ________________ b. ________________ c. ________________ d. ________________ 2. each is a more specific amount of time then the other ones -6-
  7. 7. Earth Science Earth’s History Notes Units of geological time periods Phanerozoic eon Proterozoic eon Archean eon Cenozoic Mesozoic Paleozoic cretaceous Jurassic Triassic a. epochs are more based on fossil evidence i. However, most of the geological time is void of fossil records iii. Scientists suggest the following is the geological time scale 1. Precambrian (prepaleozoic) era a. Makes up 85% of the earth’s history b. ______________________________ ______________________________ i. This is because the organisms ______ ____________________________ ____________________________ 2. Paleozoic era a. Much shorter time period b. Has an abundant of fossils c. The first vertebrates, land plants and animals developed in this era 3. The Mesozoic Era a. Was even shorter -7-
  8. 8. Earth Science Earth’s History Notes b. Fossils of dinosaurs and the earliest birds and mammals formed c. Included three periods i. Triassic ii. Jurassic iii. Cretaceous 4. The Cenozoic Era a. Most recent era b. Includes the fossils of many modern plants and mammals, even the appearance of humans i. Plate motions and mountain buildings may also be identified in this time sequence by using the reference table b. The Erosional Record i. Buried erosional surfaces show gaps in the time records of the rocks ii. It has been suggested that the fossil record would show a complete timescale and history of earth IF…………………. 1. the superposition and held absolutely true 2. no forces of destruction occurred after the the beginning of life forms iii. but it is clear that destructional forces have occurred and continue to occur iv. One of the key principles that geologists use to interpret the Earth’s geological history is the principle of uniformitarianism 1. This principle states that the geological processes that change the earth today also changed the earth in the past 2. There are many different rates and various times but patterns and agents of change stay the same c. The geological history of an area i. Using the information used in the rock record, scientist can guess the history of an area ii. To see the various rock portions if NEW YORK check out your reference guide -8-