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Earth’s history


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