Age of the Earth LCTV

1. ?
How old is the earth?

2. Pre-scientific period
AD 1600
Earth is 6000 years old.
Biblical account of
Genesis was accepted
history.

3. Speculative cosmogonies
AD 1600-1700
• Speculation on origins with little field
work on the age of the earth.
• James Ussher – Church of England
Prolific Scholar. Published
chronology to establish time/date
of creation.
“Determined” creation occurred
the night preceding Sunday, 23
October 4004 BC.

4. Steno’s Laws or Principles
1669, Niels Stensen (1638-1686), better known then and now by
his Latinized name Nicolaus Steno, formulated some rules to make
sense of rocks he viewed in Tuscany and other places.
Studied anatomy and geology. Later became a Catholic Bishop.

5. disestablishment of Genesis
AD 1700-1780
• Studies of strata (e.g. fossils,deposit type)
• Studies of earthquakes and volcanoes
• Observation of erosional forces (rain,
wind, water (rivers, seas)

6. Catastrophism vs. Uniformitarianism
• Catastrophism –earth shaped by sudden,
short-lived, violent events.
• Uniformitarianism – Present is the key to
the past. Slow, incremental changes over
long periods of time created
• Debate ranged from ~1780-1850.
• Uniform processes over time does not
mean catastrophic events do not occur.

7. Accepted earth had a long history
AD 1800
• Uniformatarians- (Hutton, Lyell)
theorized earth indefinitely old
• Catastrophists (Cuvier 1812, de
Beaumont 1852, Buckland 1836)
• Lord Kelvin in 1862 estimated the
age of the Earth to be 98 million
years (cooling model).

8. James Hutton (1726–1797)
• Father of Modern Geology
• Through observation developed ideas of the
rock cycle and uniformitarianism.

9. Jedburgh,
Scotland

10. Used in the study of sedimentary and
layered volcanic rocks.
• The principle of superposition
• The principle of original horizontality
• The principle of lateral continuity
• The principle of cross cutting relationships
• The principle of faunal succession
(fossils and index fossils) (Not Steno’s)
Stratigraphy and Relative Dating

11. Principle of Super Position
Sedimentary layers are deposited in a time sequence,
with the oldest on the bottom and the youngest on
the top.

12. Principle of Original Horizontality
Exceptions: Angle of repose, conform to existing basins.

13. Principle of Lateral Continuity
• layers of sediment initially extend laterally in all
directions; in other words, they are laterally
continuous.
• As a result, rocks that are otherwise similar, but
are now separated by a valley or
other erosional feature, can be assumed to be
originally continuous.

14. Lateral Continuity (example)

15. Lateral Continuity (example)

16. Principle of Crosscutting
• Principle of cross-cutting relationships states
that the geologic feature which cuts another
is the younger of the two features.
• Operates at various scales (large and
microscopic)

17. Principle of Crosscutting (examples)

18. Principle of Crosscutting (examples)

19. An Example of Stratigraphy

21. Unconformity

22. Faunal Succession

23. Geologic Time Scale
Eon,Era, Periods, Epochs

24. Geologic Era, Periods, Epochs

25. Limitations of relative dating
• No absolute dates
• Tectonic events can cloud relative
relationships

26. Radioactivity
• Some elements transmute to another element
• Different types of radiation are emitted:
– Alpha, Beta, Gamma

27. Elements
• pure chemical substance consisting of a single
type of atom
• distinguished by its atomic number
• number of protons in its atomic nucleus.

28. Model of Atom

29. Model of Atom

30. 3 Atoms of Different Elements.

31. Isotopes
– Isotopes – variations of an element. Different
number of neutrons in nucleus.
– Stable Isotopes.
– Unstable Isotopes.
Hydrogen Carbon Nitrogen Oxygen
1H - 99.984% 12C - 98.89% 14N - 99.64% 16O - 99.763%
2D - 0.0156% 13C - 1.11% 15N - 0.36% 17O - 0.0375%
- - - 18O - 0.1995%

32. Isotopes of Hydrogen

33. Unstable Isotopes
• Unstable isotopes = radioactive
• Nucleus that decays = Parent Isotope
• Product of the decay = Daughter Isotope
• Amount of time for ½ of the parent isotope to
decay is = ½ life of the isotope.
• If the parent isotope=daughter isotope then one
½ life has occurred.
• By calculating ratios between parent and
daughter isotopes age can be determined.

34. Parent, Daughter, Alpha

35. Radiometric Dating
• Radioactive elements were incorporated into the
Earth when the Solar System formed.
• Rocks and minerals contain tiny amounts of these
radioactive elements.
• Radioactive elements are unstable; they
breakdown spontaneously into more stable
atoms over time, a process known as radioactive
decay.
• Radioactive decay occurs at a constant rate,
specific to each radioactive isotope.
• By calculating ratios between parent and
daughter isotopes age can be determined.

36. Uranium Decay Chain

37. Uranium Decay Chain

38. Setting the radiometric clock.
• When does the radiometric clock gets set?
• Radiometric clocks are "set" when each rock
forms. "Forms" means the moment an
igneous rock solidifies from magma, a
sedimentary rock layer is deposited, or a rock
heated by metamorphism cools off. It's this
resetting process that gives us the ability to
date rocks that formed at different times in
earth history.

39. Zircon
The zircon mineral incorporates uranium and thorium atoms into its crystalline
structure, but strongly rejects lead. Therefore we can assume that the entire lead
content of the zircon is radiogenic (i.e produced by radioactive decay),

40. Zircon Decay

41. Narrowing Objects with Relative Dates

42. Early Time Line

43. Types of Radiometric Dating
Type Half Life Used for other
U235 - Pb207
U238 - Pb206
770 my
4.5 by
Granite
(Zircon,
baddeleyite)
Resistant to
lead.
Sm147-Nd143 1.06 x 1011 yrs Rocks and
meterorites
Acc. 2 million
yrs / 2.5 by
K40-Ar40 1.3 by Micas,
feldspars,
hornblends
Rb87-Sr87 50 by Old igneous /
metamorphic
Acc 30-50my
for 3 by
sample.
U234-Th230
U235-Pa231
Th230-Th232
80K yrs
34,300 yrs
Ocean
sediments
C14 5730 yrs Radiocarbon Organic

44. Advancements in Dating
• 1945 – Manhattan Project ends
• Focus of weapons research to pure
science
• Mass spectrometry
• Geochronology

45. Other types of Dating
• Fission Track
• Thermoluminescence
• Electron spin
• Cosmogenic nuclides
• Magnetostratigraphy
• Tephrochronology