Earth’s history
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Earth’s history

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    Earth’s history Earth’s history Presentation Transcript

    • Earth’s History
    • 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.
    • 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
    • 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)
    • ???? Question?????
        • Today’s atmosphere is made up of 21% oxygen but the gases of the volcanic eruptions do not contain oxygen
          • SO WHERE DID WE GET THE OXYGEN FROM?
            • 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.
    • 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
    • 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.
        • EVERY RADIOACTIVE ELEMENT DECAYS
        • 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.
          • 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
      • 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
    • 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
    • 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.
    • 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.
        • 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
      • 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
    • 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
    • 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
        • 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
    • Units of geological time periods Phanerozoic eon Proterozoic eon Cenozoic Archean eon Mesozoic Paleozoic cretaceous Jurassic Triassic eons eras periods
        • epochs are more based on fossil evidence
        • However, most of the geological time is void of fossil records
    • Geologic Time Scale
      • Scientists suggest the following is the geological time scale
      In order of creation Precambrian Paleozoic Mesozoic Cenozoic
    • 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)
    • Paleozoic
        • Much shorter time period
        • Has an abundant of fossils
        • The first vertebrates, land plants and animals developed in this era
    • Mesozoic
        • Was even shorter
        • Fossils of dinosaurs and the earliest birds and mammals formed
          • Included three periods
              • Triassic
              • Jurassic
              • Cretaceous
    • 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