Earth’s history

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Earth’s history

  1. 1. Earth’s History
  2. 2. Introduction <ul><ul><li>As we already learned the earth is always changing </li></ul></ul><ul><ul><li>The history of the earth is told by the Earth’s Geological events </li></ul></ul><ul><ul><li>It is up to the scientist to figure out the puzzle of these geological events. </li></ul></ul>
  3. 3. Early Earth <ul><ul><li>There is evidence that states that the atmosphere and the oceans of the early earth began to form from gasses coming from volcanic eruptions in the earth’s interior. </li></ul></ul><ul><ul><li>There were large amounts of </li></ul></ul><ul><ul><ul><li>Water vapor </li></ul></ul></ul><ul><ul><ul><li>Carbon dioxide </li></ul></ul></ul><ul><ul><ul><li>Nitrogen </li></ul></ul></ul><ul><ul><ul><li>And other gases </li></ul></ul></ul>
  4. 4. What is Outgassing? <ul><li>- That came out of the earth from a process called outgassing </li></ul><ul><ul><ul><li>The vapor was the source of water for the atmosphere and the oceans </li></ul></ul></ul><ul><ul><li>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. </li></ul></ul><ul><ul><li>What is the proof to this? </li></ul></ul><ul><ul><ul><li>Scientists have studies sedimentary marine rocks that prove this concept of an early ocean. ( 4 billions years ago) </li></ul></ul></ul>
  5. 5. ???? Question????? <ul><ul><li>Today’s atmosphere is made up of 21% oxygen but the gases of the volcanic eruptions do not contain oxygen </li></ul></ul><ul><ul><ul><li>SO WHERE DID WE GET THE OXYGEN FROM? </li></ul></ul></ul><ul><ul><ul><ul><li>Scientists believe that the early oceans contained green plants. These green plants as we know get their food from photosynthesis. </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Photosynthesis produces extra oxygen that went into the atmosphere over millions of years. </li></ul></ul></ul></ul></ul>
  6. 6. Sequence of Geological Events <ul><li>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 </li></ul><ul><li>Relative age is concerned with the sequence of events that occurred in an area </li></ul><ul><ul><li>As shown in the appearance of the rock layers </li></ul></ul><ul><ul><li>Relative age is not really concerned with the age of the rocks </li></ul></ul><ul><ul><li>This method uses </li></ul></ul><ul><ul><li>sedimentary rock layers </li></ul></ul><ul><ul><li>igneous extrusions and intrusions </li></ul></ul><ul><ul><li>faults </li></ul></ul><ul><ul><li>folds </li></ul></ul><ul><ul><li>continuity </li></ul></ul><ul><ul><li>similarities of rock </li></ul></ul><ul><ul><li>fossil evidence </li></ul></ul><ul><ul><li>and volcanic time markers </li></ul></ul><ul><li>As clues to determine what was the probable sequence of events </li></ul>
  7. 7. Absolute Age <ul><ul><ul><li>The actual age of a rock or a fossil is called absolute age </li></ul></ul></ul><ul><ul><ul><li>The best way and more precise way of figuring out how old a rock or a fossil is uses a technique called radioactive dating. </li></ul></ul></ul><ul><ul><li>EVERY RADIOACTIVE ELEMENT DECAYS </li></ul></ul><ul><ul><li>How does this work? </li></ul></ul><ul><ul><ul><li>Every radioactive “parent” element release radiation until it breaks down (decays) into a stable daughter element. </li></ul></ul></ul><ul><ul><ul><li>Sometimes this changing process goes through steps </li></ul></ul></ul><ul><ul><ul><li>We also know how long it would take for a radioactive isotope to decay. </li></ul></ul></ul><ul><ul><ul><li>We use a process of half life. Since we know how long the half life ( time takes ½ the isotope to decay) is we can then figure out how old a rock is based upon what stage of decay it is in. </li></ul></ul></ul>
  8. 8. <ul><ul><ul><li>The law of superposition </li></ul></ul></ul><ul><ul><ul><ul><li>This states the bottom layer of a group of horizontal layers of rocks is the oldest. </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>This is used to determine the sequence of when the sedimentary rocks were formed. </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>This works as long as the group was not overturned not had an older rock put over it </li></ul></ul></ul></ul></ul>
  9. 9. <ul><li>Igneous Intrusions and Extrusions </li></ul><ul><ul><li>Igneous Intrusions </li></ul></ul><ul><ul><ul><li>formed when magma is injected into older rock layers in the crust </li></ul></ul></ul><ul><ul><ul><li>younger than rock they are found in </li></ul></ul></ul><ul><ul><ul><li>look for contact metamorphic rock in layer above and below the intrusion </li></ul></ul></ul><ul><ul><li>Igneous Extrusions </li></ul></ul><ul><ul><ul><li>rocks that formed from lava on the surface of the earth </li></ul></ul></ul><ul><ul><ul><li>younger than rock layers below </li></ul></ul></ul><ul><ul><ul><li>look for contact metamorphic rock on the bottom only </li></ul></ul></ul><ul><ul><li>Why do we look at the metamorphic rock near these two rock formations? </li></ul></ul><ul><ul><ul><li>The reason is contact metamorphism – (the rock forming due to the contact of lava) will be younger then the rocks that it goes through </li></ul></ul></ul>
  10. 10. Folds, Faults, & Joints <ul><ul><ul><li>Folds </li></ul></ul></ul><ul><ul><ul><ul><li>bends in the rock layers </li></ul></ul></ul></ul><ul><ul><ul><ul><li>occur after the rock layers formed </li></ul></ul></ul></ul><ul><ul><ul><li>Faults </li></ul></ul></ul><ul><ul><ul><ul><li>cracks in rock layers where some movement has taken place </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Faults produce offset layers. </li></ul></ul></ul></ul><ul><ul><ul><li>Joints </li></ul></ul></ul><ul><ul><ul><ul><li>Are immovable cracks </li></ul></ul></ul></ul><ul><ul><ul><li>These three rock layer characteristics occur due to changes in the temperature and pressure </li></ul></ul></ul><ul><ul><ul><li>These three rock characteristics are also younger than the rocks in which they appear. </li></ul></ul></ul><ul><ul><ul><li>Since the rocks that fold faults or joints are there before these things occur </li></ul></ul></ul>
  11. 11. Internal Characteristics <ul><ul><ul><li>Fragments that occur in a rock as we can understand are older than the rock itself (since the rock was formed through these fragments) </li></ul></ul></ul><ul><ul><ul><li>Cracks and veins in a rock are younger then the rock in which they are found </li></ul></ul></ul><ul><ul><ul><li>Veins – are mineral deposits that fill up a crack in a rock </li></ul></ul></ul><ul><ul><ul><li>Sedimentary rocks are older than the sedimentary layers and the cement that keep them together. </li></ul></ul></ul>
  12. 12. Unconformity <ul><ul><li>Is the break in geological history of a rock series </li></ul></ul><ul><ul><li>They are found between two ages of rock levels </li></ul></ul><ul><ul><li>Usually these gaps are formed from erosion and non deposition </li></ul></ul><ul><ul><li>It looks like a buried Erosional surface </li></ul></ul><ul><ul><li>Since the rock stopped building up erosion occurred on the top layer and then a new age group of rocks were formed. </li></ul></ul>
  13. 13. <ul><ul><li>We use different correlating techniques to find out how old a rock really is </li></ul></ul><ul><ul><li>You have to be careful though to use facts and not inferences when figuring out this information </li></ul></ul><ul><ul><ul><li>Correlation is the act of matching rocks of similar age in different places </li></ul></ul></ul><ul><ul><ul><ul><li>This is best done when rocks are not covered in dirt and plants </li></ul></ul></ul></ul><ul><ul><ul><ul><li>This can be so easy by identifying a certain mineral type, color and then searching for it in different places </li></ul></ul></ul></ul>
  14. 14. <ul><li>this is using the remains of animals that are known to have lived and died in a certain time period </li></ul><ul><li>If we find one of these fossils then we can look for rock layers that look the same and figure out how old it is </li></ul><ul><li>We also use Index fossils to decipher rock records </li></ul><ul><li>Organism that classified as index fossils are found only in certain rocks </li></ul><ul><ul><li>How does a fossil fit the index profile </li></ul></ul><ul><ul><ul><ul><li>Easily recognizable </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Abundant </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Have been found in a wide geographic area </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Existed on earth for a brief period of time </li></ul></ul></ul></ul>
  15. 15. Volcanic Time Marker <ul><ul><ul><ul><li>When a volcano erupts it leaves a layer of volcanic ash is deposited over the area </li></ul></ul></ul></ul><ul><ul><ul><ul><li>This may be a time marker if we find a layer of ash in the layers of the rocks and the time of the volcanic eruption is known </li></ul></ul></ul></ul><ul><ul><ul><ul><li>This time marker will be very helpful determined the ages of rocks below and above it </li></ul></ul></ul></ul>
  16. 16. Problems with Correlation <ul><ul><li>It seems based upon what we have just learned that figuring out a geological time line is very simple. </li></ul></ul><ul><ul><li>However, it can lead to misinformation </li></ul></ul><ul><ul><ul><li>With very careful study of 2 like rock formation they might still be different ages. </li></ul></ul></ul><ul><ul><ul><li>Also , in the same rock formation their might be rocks of different ages </li></ul></ul></ul>
  17. 17. <ul><ul><li>Rock Record </li></ul></ul><ul><ul><ul><li>As we just learned that scientist use index fossils (guide fossils ) to tell how old a rock is. </li></ul></ul></ul><ul><ul><ul><li>Scale of geological time </li></ul></ul></ul><ul><ul><ul><ul><li>scientists have organized the geological time scale </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>eons </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>eras </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>periods </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>epochs </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><li>each is a more specific amount of time then the other ones </li></ul></ul></ul></ul>
  18. 18. Units of geological time periods Phanerozoic eon Proterozoic eon Cenozoic Archean eon Mesozoic Paleozoic cretaceous Jurassic Triassic eons eras periods
  19. 19. <ul><ul><li>epochs are more based on fossil evidence </li></ul></ul><ul><ul><li>However, most of the geological time is void of fossil records </li></ul></ul>
  20. 20. Geologic Time Scale <ul><li>Scientists suggest the following is the geological time scale </li></ul>In order of creation Precambrian Paleozoic Mesozoic Cenozoic
  21. 21. Precambrian/ Pre Paleozoic <ul><ul><li>Makes up 85% of the earth’s history </li></ul></ul><ul><ul><li>Very little fossil evidence from this time period </li></ul></ul><ul><ul><li>This is because the organisms that were around had soft bodies , simple, and small ( ex; algae bacteria) </li></ul></ul>
  22. 22. Paleozoic <ul><ul><li>Much shorter time period </li></ul></ul><ul><ul><li>Has an abundant of fossils </li></ul></ul><ul><ul><li>The first vertebrates, land plants and animals developed in this era </li></ul></ul>
  23. 23. Mesozoic <ul><ul><li>Was even shorter </li></ul></ul><ul><ul><li>Fossils of dinosaurs and the earliest birds and mammals formed </li></ul></ul><ul><ul><ul><li>Included three periods </li></ul></ul></ul><ul><ul><ul><ul><ul><li>Triassic </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Jurassic </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Cretaceous </li></ul></ul></ul></ul></ul>
  24. 24. Cenozoic <ul><ul><li>Most recent era </li></ul></ul><ul><ul><li>Includes the fossils of many modern plants and mammals, even the appearance of humans </li></ul></ul><ul><ul><li>Plate motions and mountain buildings may also be identified in this time sequence by using the reference table </li></ul></ul>
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