1. Geology
By Mr. Joydeep Saha

2. Geological Time - Start movie at present and go back in time.
Motion pictures are generally projected at 32 frames per second. Therefore, each frame (image) is on the screen for only split second- let each frame represent 100 years.
Start movie at present and go back in time.
The Declaration of Independence would show up 1/16 of a second into the movie.
The Christian era (BC-AD boundary) would be 3/4 of a second into the movie.
The most recent Ice Age would be 7 seconds into it.
The movie would run about 6 hours before we got to the end of the Mesozoic era (extinction of the dinosaurs).
We'd have to watch the movie for about 2 days to see the beginning of the Paleozoic era (macroscopic life).
The whole movie (to the beginning of geologic time on Earth) would be approximately 16 days long!

3. Geologic Time • • Two ways to relate time in geology: > >
Relative
Relative
: Placing events in a
: Placing events in a
sequence based on their positions
sequence based on their positions
in the geologic record.
in the geologic record.
>
>
Chronologic
Chronologic
: Placing a specific
number of years on an event or rock
sample.
sample.

4. Geologic Time Scale • A combination of the two types of age`
determinations
> A
relative
sequence of lithologic units -
established using logical principles
>
Measured against a framework of
chronologic
dates.

5. Geologic Time and the "geologic column" • •
Developed using logical rules to establish relative
sequences of events - -
superposition - -
cross-cutting relationships - -
original horizontality - -
lateral continuity
Added to as new information is obtained and
data is refined • •
Use of fossils for correlation and age determination - - • •
Numerical Dates attached to strata after the
development of Radiometric techniques - -

6. The Geologic Time Scale (1:2)

7. The Geologic Time Scale (2:2)

8. Relative Dating Methods•
Determines the relative sequence of events.
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which came first, which came last.
>
no numeric age assigned •
6 Relative age principles:
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Superposition
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Original Horizontality,
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Lateral continuity
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Cross-cutting Relationships
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Inclusions
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Fossil succession.
Those in yellow are most useful

9. History of Historical Geology-
Fundamental Principles of Relative Time
>
Principle of Superposition
Principle of Original Horizontality
Principle of Original Lateral Continuity

10. Law of Superposition • •
In undisturbed strata, the layer on the bottom is
oldest, those above are younger.

11. Original Horizontality• •
Sediments are generally deposited as
horizontal layers.
Lateral Continuity • •
Sediment layers extend laterally in all
direction until they thin & pinch out as
they meet the edge of the depositional
basin.

12. Charles Lyell included description and use of • •
1st Principles of Geology text - -
included description and use of
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>
principles of cross-cutting relationships
principles of cross-cutting relationships
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>
principles of inclusions
principles of inclusions • •
relative time tools
relative time tools

13. Cross-cutting Relationships
That which cuts through is younger than the
Object that is cut
dike cuts through
granite is cut

14. Relative Ages of Lava Flows and Sills

15. Principle of Inclusions•
Inclusions (one rock type contained in another rock type) are
older than the rock they are embedded in. That is, the younger
rock contains the inclusions

16. Principle of Inclusions

17. Faunal/Floral Succession• •
Fossil assemblages (groupings of fossils)
succeed one another through time.

18. relating rocks in one location to those in
• Correlation-
relating rocks in one location to those in
another using relative age stratigraphic
principles - -
Faunal Succession - -
Superposition
Lateral Continuity - - - -
Cross-cutting

19. Unconformities • • surfaces represent a long time. Hiatus
a time when rocks were not
deposited or
a time when rocks were
eroded
Hiatus
the gap in time represented
in the rocks by an uncon-
formity
3 kinds
Angular Unconformity
Nonconformity
Disconformity

20. Disconformities A surface of erosion or non-deposition between
Parallel sedimentary rock beds of different ages

21. Angular Unconformities Angular Unconformities• An
angular unconformity
is an erosional surface on tilted
or folded strata, over which younger strata have been deposited.

22. Nonconformities A nonconformity is an erosional surface on igneous or
metamorphic rocks which are overlain by sedimentary rocks.

23. Breakout in to groups and discuss the sequence observed here

24. Age Estimates of Earth Counting lifetimes in the Bible
Comparing cooling rates of iron pellets.
Determine sedimentation rates & compare
Estimate age based on salinity of the ocean.
all age estimates were off by billions of years
some were more off than others!

25. Absolute Dating Methods
Radioactive
Decay sequences
acts as an atomic clock
we see the clock at the end of its cycle
analogous to starting a stopwatch
allows assignment of numerical dates to
rocks.
>
>
decay
) into
Radioactive isotopes change (
daughter isotopes at known rates.
rates vary with the isotope
e.g., U , K , C, etc. + +
235 40 14

26. Decay
unstable nuclei in parent isotope emits
subatomic particles and transform into
another isotopic element (daughter).
does so at a known rate, measured in the
lab
Half-life
The amount of time needed for one-half of a
radioactive parent to decay into daughter
isotope. •

27. Rate of Decay t All atoms are parent isotope or some1 3
All atoms are parent isotope or some
known ratio of parent to daughter
1 half-life period has elapsed, half of the
material has changed to a daughter
isotope (6 parent: 6 daughter) 2
2 half-lives elapsed, half of the parent
remaining is transformed into a daughter
isotope (3 parent: 9 daughter)
3 half-lives elapsed, half of the parent
isotope (1.5 parent: 10.5 daughter)
We would see the rock at this point.

28. 100 % parent remaining Parent Parent Daughter Daughter 50 25 13
Radioactive Isotopes
Radioactive Isotopes • •
analogous to sand in an hour glass
analogous to sand in an hour glass - -
we measure how much sand there is
we measure how much sand there is
>
>
represents the
represents the
mass of elements
mass of elements - -
we measure the ratio of sand in the bottom to sand in the top
we measure the ratio of sand in the bottom to sand in the top - -
at the end (present)
at the end (present)
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>
daughter (b) and parent (t)
daughter (b) and parent (t) - -
we know at what rate the sand falls into the bottom
we know at what rate the sand falls into the bottom
>
>
the half life of the radioactive element
the half life of the radioactive element - -
how long would it take to get the amount sand in the observed
how long would it take to get the amount sand in the observed
ratio starting with all of it in the top?
ratio starting with all of it in the top?
100
Parent
Parent
% parent remaining
Daughter
Daughter 50 25 13
time >

29. Five Radioactive Isotope Pairs Five Radioactive Isotope Pairs
Effective
Dating Range
Minerals and
Isotopes
Half-Life
of Parent
(Years)
Rocks That Can
Parent
Daughter
(Years)
Be Dated
Uranium 238
Lead 206
4.5 billion
10 million to
Zircon
4.6 billion
Uraninite
Uranium 235
Lead 207
704 million
Muscovite
Thorium 232
Lead 208
14 billion
48.8 billion
Biotite
Potassium feldspar
Rubidium 87
Strontium 87
4.6 billion
10 million to
Whole metamorphic
4.6 billion
or igneous rock
Potassium 40
Argon 40
1.3 billion
100,000 to
Glauconite
4.6 billion
Muscovite
Biotite
Hornblende
Whole volcanic rock

30. Carbon-14 dating is based on the Carbon-14 dating is based on the
Radiocarbon and Tree-
Ring Dating Methods
Carbon-14 dating is based on the
Carbon-14 dating is based on the • •
ratio of C-14 to C-12
ratio of C-14 to C-12
in an organic
sample.
sample.
>
>
Valid only for samples less than 70,000
Valid only for samples less than 70,000
years old.
years old.
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>
Living things take in both isotopes of
Living things take in both isotopes of
carbon.
carbon.
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>
When the organism dies, the "clock" starts.
When the organism dies, the "clock" starts.
Method can be validated by cross-checking with tree rings

31. Carbon 14 Cycle

32. Recognizing Patterns of change Walther's Law•
The vertical sequence is repeated by the horizontal
sequence -
walking from A to B to C to the Coast you would encounter the
rocks that would be encountered by drilling a core into the
earth at any point (A, B, or C)

33. Facies Diagram • distribution of lithofacies (rock-types) •
these are associated with their respective EOD •
biofacies are similar but refer to fossils rather than
rock types

34. Eustasy, relative sea-level, and relative position of lithofacies•
Eustasy= changes in volume of water in ocean
lithofacies depend on -
sea-level
land level
geometry of coast
sediment supply
Vail Curve
an attempt at global
correlation of
lithologies
for better production
of petroleum resources

35. Rock designations • Rock units called Lithostratigraphic units-
described in terms of Group, Formation, & Member
>
each term has specific meanings in geological parlance
Formation
a mappable lithostratigraphic unit
has a location for identifying the type-section
has a rock designation describing the lithology
sometimes not all the same lithology
in which case the term "Formation" takes the place of lithologic
type
Groups are composed of several formations
Members are distinctive units within a formation
group is largest and contains formations and members
formations are next and contain members

36. Magnetization of Volcanic Rocks
Successive lava flows stack up one on top of another, each lava flow recording the Earth’s polarity at the time at which it formed
Each lava flow can also be dated using radioactive elements in the rock to give its age

37. Magnetization of Volcanic Rocks
Magnetic patterns of ocean floor
What does magnetic polarity of lava flows tell us?
Plotting the polarity of different lava flows against their ages gives us a record of the Earth’s polarity at different times in the past
Timing of polarity reversals (north to south; south to north) seems random
Reversals probably caused by changes in the flow of iron-rich liquid in the Earth’s outer core

38. Earth’s Magnetic Field
Earth’s magnetic field acts like giant bar magnet, with north end near the North Pole and south end near the South Pole
Magnetic field axis is now tilted 11o from vertical (tilt has varied with time) so that magnetic poles do not coincide with geographic poles (but are always near each other)
Inclination of magnetic lines can also be used to determine at what latitude the rock formed
Magnetic field is caused by dynamo in outer core:
Movements of iron-rich fluid create electric currents that generate magnetic field

39. Magnetization Patterns on the Seafloors
Atlantic Ocean floor is striped by parallel bands of magnetized rock with alternating polarities
Stripes are parallel to mid ocean ridges, and pattern of stripes is symmetrical across mid ocean ridges (pattern on one side of ridge has mirror opposite on other side)

40. Magnetization Patterns on the Seafloors
Magma is injected into the ocean ridges to cool and form new rock imprinted with the Earth’s magnetic field
Seafloor is then pulled away from ocean ridge like two large conveyor belts going in opposite directions – seafloor spreading

41. Other Evidence of Plate Tectonics
Earthquake epicenters outline plate boundaries
Map of earthquake epicenters around the world shows not random pattern, but lines of earthquake activity that define the edges of the tectonic plates

42. Other Evidence of Plate Tectonics
Deep earthquakes
Most earthquakes occur at depths less than 25 km
Next to deep-ocean trenches, earthquakes occur along inclined planes to depths up to 700 km
These earthquakes are occurring in subducting plates

43. The Grand Unifying Theory
Tectonic cycle

44. Plate Tectonics and Earthquakes
Most earthquakes can be explained by plate tectonics:
Divergent plate boundaries
Divergent motion and high temperatures cause rocks to fail easily in tension
Earthquakes are small and generally non-threatening
Transform plate boundaries
Plates slide past each other in horizontal movement, retarded at irregularities in plate boundaries
Energy required to move plates is released as large earthquakes
Convergent plate boundaries
Great amounts of energy are required to pull a plate back into the mantle or push continents together
Largest earthquakes are generated at convergent boundaries

45. Plate Tectonics and Earthquakes
Examine example of Pacific plate:
Created at spreading centers on eastern and southern edges, producing small earthquakes
Slides past other plates on transform faults (Queen Charlotte fault, Canada; San Andreas fault, California; Alpine fault, New Zealand), generating large earthquakes
Subducts along northern and western edges, generating enormous earthquakes

46. Subduction Zones
Tokyo, Japan, 1923 – one of world’s most deadly disasters (probably about 144,000 people killed)
Series of earthquakes, with principal one worst of year globally
Tsunami 11 m high hit city
Fires raced through city for 2½ days, destroying 71% of Tokyo and all of Yokohama
38,000 people were killed by fire, crowded into a park that was consumed by fire from three sides

47. Continent-Continent Collisions
Collision of India into Asia
India has moved 2,000 km north into Asia from initial contact
Pre-collision, Indian and Asian crusts were 35 km thick
Now crust under area of Tibetan plateau is 70 km thick and highest-standing continental area on Earth
India continues to move 5 cm/year into Asia, along a 2,000 km front, affecting India, Pakistan, Afghanistan, Tibetan Plateau, eastern Russia, Mongolia and China with great earthquakes, and pushing parts of China to the east and southeastern Asia farther to the southeast

48. Question????

49. Test Write two ways to relate time in Geology.
Write any two relative age principle.
How age of earth can be estimated?
What is Half Life?
What does magnetic polarity of Lava flows tell us?