Interpreting Geologic History Updated
Upcoming SlideShare
Loading in...5
×
 

Interpreting Geologic History Updated

on

  • 1,673 views

 

Statistics

Views

Total Views
1,673
Views on SlideShare
1,665
Embed Views
8

Actions

Likes
4
Downloads
98
Comments
0

3 Embeds 8

http://www.slideshare.net 4
http://www2.eboard.com 3
http://www3.eboard.com 1

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

Interpreting Geologic History Updated Interpreting Geologic History Updated Presentation Transcript

  • Interpreting Geologic History
  • THE PRINCIPLE OF UNIFORMITY:
    • Geologists can infer events of the past by
    Looking at features of rocks and rock outcrops
  • Uniformitarianism (Principle of
    • states that the forces that acted upon the
    • ___________ crust…
    Uniformity) Earth’s
    • in the __________ are the same as those that are ____________
    • today.
    past active ** THE KEY TO THE PAST IS THE PRESENT**
  • Relative Dating Techniques
  • 5 Basic Laws:
    • 1. Law of Original Horizontality
    • 2. Law of Superposition
    • 3. Law of Inclusions
    • 4. Law of Cross-Cutting Relationships
    • 5. Law of Original Lateral Continuity
  • Law of Original Horizontality
    • Strata is originally
    • deposited in flat horizontal layers because sedimentary particles settle from air and water under the influence of gravity
  • Law of Original Horizontality
    • If strata are ___________, then they must have suffered some kind of disturbance after they were deposited.
    Grand Canyon Western Iran Steeply Inclined
  • THE LAW OF SUPERPOSITION:
    • the principle that the _________ layers in a sequence of rock strata must have been deposited __________ the layers above, unless the rock strata have been ___________ or___________
    bottom before disturbed uplifted
    • The _______ rocks are found at the bottom.
    • Geologists can date the
    • _________ ages of the strata from
    • ________ to __________
    older relative oldest youngest
  • oldest youngest
  • Law of Superposition
    • Therefore the order of deposition is from the bottom upward.
  • Law of Inclusions
    • A rock must first exist in order to be weathered, deposited and cemented as a _____ in another rock. Therefore…
    clast
    • If rock is composed of _____________, the rock fragments must be ___________ than the rock in which they are found.
    fragments older
  • Law of Inclusions Which is older the Granite or the Sandstone? In figure A? In figure B? Sandstone is older Granite is older
    • The law of inclusions also applies to fossils preserved in the bedrock.
    • _________ are any naturally preserved remains or impressions of living things.
    Fossils
  •  
  •  
  •  
  •  
  •  
  •  
  •  
  •  
    • They are found in _______________ because
    • _____________________
    • ____________
    Sedimentary rock Heat & pressure in igneous and metamorphic rock destroys them
  • FOSSILS GIVE US INFORMATION ABOUT THE ANCIENT ENVIRONMENT AND CLIMATE
  • Law of Cross-Cutting Relationships
    • Any __________ or ______, must be younger than all rocks through which it cuts. Simply put, the body of rock that is cross-cut had to be there first in order to be cut by an intruding igneous body or fault.
    Igneous rock fault
    • In general rock is always_________ than the process that changed it.
    older
  • Some Processes Include:
    • folds
    • faults
    • tilts
    • intrusions
    • extrusions
  • Sedimentary layers (the law of original horizontality)
  • Sedimentary layers
  • Sedimentary layers
  • Sedimentary layers
  • Sedimentary layers
  • The fault came after the rock was formed
  • Sedimentary layers The tilt came after the the rock was formed
  • The extrusion came after the rock was formed 1 2 3 4 5 Contact metamorphism
  • 1 2 3 4 5 6 The extrusion came after the lower layers were formed but…. Before the top layer
  • 1 2 3 4 5 This intrusion came after all the layers
  •  
    • These changes can lead to exceptions to the Law of Superposition:
    • a.An __________ is
    • an igneous rock that formed from lava on the surface of the crust.
    extrusion
    • An __________ must be younger than the strata below it, but ________ than any layers above.
    extrusion older
    • b. __________ are created when molten rock (________) is injected into older rock layers in the crust.
    intrusions magma
    • _____________ are
    • _____________ than
    • all the rock layers in contact with them.
    Intrusions younger
    • c. _______ are bends
    • in the rock strata. ________ can overturn rock strata so that ________ rock lies on top of _________ rock.
    Folds folding older younger
  •  
  •  
    • d. _______ are cracks
    • in rock strata.
    • _______ produce offset layers.
    Faults Faults
    • d. _______ are cracks
    • in rock strata.
    • _______ produce offset layers.
    Faults Faults
    • Rock strata must be
    • ________ than the process that changed it.
    older
    • _________, ________ and ________ ___________
    • are features created after rock or sediment has been deposited.
    cracks veins natural cement
  •  
  • Law of Original Lateral Continuity
    • . When sediment is dumped by an agent of erosion, strata extends from the source until it gradually thins to zero, or until it reaches the edges of the basin of __________.
    deposition
  • Law of Original Lateral Continuity
  • Law of Original Lateral Continuity
    • This concept enables us to correlate outcrops of strata that has been dissected by processes of ________.
    erosion
  • CORRELATION OF ROCK STRATA:
    • Correlation is
    Matching similar rock strata at different locations to see if they formed at the same time
  • Ways to correlate rock formations:
    • “ Walking the outcrop”
    • is done by
    Walking from end to end
    • This is correlation by
    continuity
  • You can match the rock strata in one location with rock strata in more distant locations by Comparing , c o l o r texture composition sequence of layers
  • Time correlation compares ____________ contained in the rock strata index fossils 1 2 3 4 4 5 6 3
  • The best index fossils:
    • a. _________________
    • b. _________________
    Exist for a brief period of time are widespread
  • Which fossil would make the best index fossil? Found in only 1 layer (short lived) Found in all samples (widespread)
  • Another way of correlating layers by time is through ___________________ Volcanic ash falls
  • These ash falls are very ________ events. A single layer of ______ can be found over a large area, this allows geologists to make a__________________ from one location to another at the position of a common ash fall. brief ash time correlation
  • GEOLOGIC TIME SCALE:
    • A. Geologists noticed that rock _________ can be identified by the fossils they contained.
    formations
    • They also found that certain __________ were consistently located ________ or _________ other formations.
    formations above below
    • From these observations they established a
    • ______ ____ ______
    • with a sequence of fossil groups from ______ to
    • ______________
    relative time scale oldest youngest
    • Each of these groups was named for a location where its ____________ ______ could be observed in the rocks.
    Characteristic fossil Example: Devon fossil “ Devonian ” found in Devon England
    • Further observations from around the world established a
    • ________ _____ _____
    Geologic time scale
    • Based on __________________________________
    • and ________________
    • ________ _____ _____
    Inferred positions of Earth’s Landmasses Major Geologic Events (ex. Ice ages & Orogenys)
    • An ________ is the process of mountain building
    • TURN TO PAGES 8 & 9 IN YOU ESRT!
    Orogeny
  •  
  •  
  • GEOLOGIC EVENTS OF THE PAST:
    • _________ causes gaps in the geologic record.
    Erosion MISSING LAYERS
    • When a new layer
    • of rock is laid down on a surface that has been _______ it forms a buried erosional surface or an
    • ___________________
    Eroded, unconformity
  • NEW BOTTOM LAYER APPEARS (EMERGES)
  • LAYER C IS MISSING EROSION
  • EROSION
  • THE UNCONFORMITY IS THE BURIED EROSIONAL SURFACE BETWEEN B AND D
  •  
  •  
  • ACTIVITY WHICH IS OLDER
  • VII. RADIOACTIVE DATING:
    • A. Fossils enabled geologists to give ___________ time,
    relative
  • Relative Time
    • Compares rock ages to _______________.
    • Ex: The Limestone is older than the Sandstone.
    each other
  • However,
    • B. Measurements of natural ___________in ( metamorphic and igneous) rocks have allowed the _________ time scale to be an ________ time scale.
    geologic absolute radioactivity
    • The _________ _____ of an object is measured in years.
    • Ex: The limestone formed 5 mya and the sandstone formed 2 mya
    absolute age
    • C. Chemical elements often have several forms called _______________
    isotopes
  • ISOTOPE: An unstable element with different number of neutrons than a normal (stable) element. (Its unstable so wants to change to stable)
  • EX. C C 6 6 12 14 6 protons 6 protons 6 neutrons Unstable 8 neutrons
  • EX. C C 6 6 12 14 6 protons 6 protons 6 neutrons 8 neutrons unstable
  • D. If the nucleus has more or fewer than the normal number of ____________, the isotope may be ____________ neutrons radioactive (unstable)
    • E. A radioactive isotope will break down naturally into a lighter element called
    • _____ ________ which is stable.
    decay product
  • This process is called… Radioactive Decay
  • RADIOACTIVE DECAY:
    • WHEN AN UNSTABLE ________ ELEMENT CHANGES INTO A COMPLETELY DIFFERENT (BUT STABLE) __________ ELEMENT
    DAUGHTER PARENT
    • F. A sample starts out at “Time zero” with _______ Percent of radioactive material.
    100
    • Time Zero: when the sample is originally formed by cooling or solidification of igneous or metamorphic rock
    • As time goes by and the sample gets older, the radioactive element decay, and _______ radioactive atoms remain in the sample.
    fewer
    • Therefore, the higher the ratio of decay product to the radioactive element, the _____ the sample.
    older
    • The ratio between the mass of the radioactive element and its decay product in a sample is the _______________
    decay product ratio
    • G. The decay of the parent atoms in a sample to daughter atoms is a _________ process…
    random
    • That happens at _____________ rates for different radioactive elements. Lets model this with pennies…
    different
    • H. The rate of decay of a radioactive element is measured by its’ _______ _________
    half life
  • HALF-LIFE:
    • THE AMOUNT OF TIME IT TAKES FOR
    • HALF OF THE UNSTABLE
    • ATOMS IN A SAMPLE TO CHANGE TO THE STABLE DECAY PRODUCT
  • Original=100% Decay product=0% 100/0 Or 1 to 0
  • Original=50% Decay product=50% 50/50 Or 1 to 1 After one Half-life:
  • Original=25% Decay product=75% 25/75 Or 1:3 After two Half-lives:
  • Original=12.5% Decay product=87.5% 12.5/87.5 After three Half-lives:
  • Original=6.25% Decay product=93.75% 6.25/93.75 After four Half-lives:
  • N 14 Ar 40 Pb 206 Sr 87 5.7 x 10 3 1.3 x 10 9 4.5 x 10 9 4.9 x 10 10 Element Decay Product Half-life
    • H. Calculating the age of a rock:
    • 1. What would be the age of the rock if it has equal amounts of C-14 and its decay product N-14?
  • One half life has gone by
    • 5.7 x 10 3 years
    • or 5,700 years
    • 2.What % of the sample is radioactive after the following half-lives,
    • 1 half-life
    • 2 half-lives
    • 3 half-lives
    50% 25% 12.5%
    • 3. After 11,200 years how much C-14 would remain in a 10 gram sample?
    25% or 2.5 grams 1/4 of the original amount
  • I. Selecting the Best Radioactive Element:
    • 1. Under 50,000 years
    • 2. Over 50,000 years
    Use Carbon-14 Use Uranium-238
    • Carbon 14 is used for dating
    • organic material
    • And ancient wood fires
    • “Time Zero” for carbon dating begins when the organism ___________ or when the ________ burns out.
    dies wood fire
  •