THE LANGUAGE OF THE
EARTH – PART VII
Geochronology
Methods for Determining the
Relative and Absolute Age of
Rocks
Relative Age Dating - Superposition
Principles of Faunal
Succession
and Faunal
Assemblage
Index Fossils
- Widespread distribution
- Restricted, known time of
existence
- Common to many
environments
Principle of Cross-cutting Relationships
Global Time Markers
Volcanic Ash Eruptions
Global Time Markers
Magnetic Reversals
Global Time Markers
Meteor Impacts
mudstone-impact layer
K-T Boundary
coal
K-T impact site
Global Time
Markers
Climate Change
Gaps in the Geological Record
Unconformities
Creating
Unconformities
Gaps in the Minnesota Timescale
Regional Correlation of Units
Piecing the Rock Record Together
Absolute Age Determinations
Radiometric Dating
Radioactive Isotopes
Radioactive Decay
Radioactive Decay
Half-life
Zircon
ZrSiO4
U substitutes
for Zr, but Pb
does not.
Rb-Sr Dating of a Granite
 87Sr; 86Sr is stable
Rb – chemically substitutes for K
Sr – chemically substitutes for Ca
87Rb
Isochron
t=2
t=1
87Sr/86Sr
Metamorphism
at t=1
87Sr/86Sr°(m)
t=0
87Sr/86Sr°
87Rb/86Sr
Ca-plagioclase
Granite whole rock
K-feldspar
Biotite (K-rich)
GEOPUZZLE 1
GEOPUZZLE 2
GEOPUZZLE 3