EAS 210: Chapter 8

What is relative dating?

- sequence in which stuff happens

What is uniformitarianism?

- Earthly processes today are similar to those which happened historically
- helps us understand the history of rocks

What are the 7 principles of relative dating?

1. Superposition
2. Original horizontality
3. Lateral continuity
4. Cross-cutting relationship
5. Inclusions
6. Contact metamorphism
7. Fossil succession

What is the law of superposition?

- In undeformed sedimentary rock, Each layer is older than the one above and younger than the one below
- Applied to layers of lava flows and layer of volcanic ash

What is the principle of original horizontality?

- Most sedimentary rocks formed in layers that are horizontal or close to horizontal
- This is because lakes and sea surfaces are horizontal
- Cross-bedding can occur up to 15 degrees

What are the principles of cross-cutting relationships?

- Intrusions are younger than the rocks they intrude
- A fault is younger than the rock that is fracture

What is the principle of inclusions?

- Inclusions are fragments of one rock unit that are enclosed in another
- Layer containing inclusions must be younger than the inclusions

What is unconformity?

- The boundary between igneous rock and sedimentary rock
- Represents missing time in the geological record

What is a nonconformity?

- contacts between sedimentary and igneous rocks
- exposure, weathering and erosion of intrusive igneous rock being filled with the deposition of sedimentary rock

What is an intrusion?

- Layers which include intrusions are younger
- Pieces of sedimentary rocks fall into magma and become inclusions within rock

What is an angular uncomformity?

- the difference in angle between rocks of different ages
- Time is missing from geological history recorded
- evidence of past mountain building

What is a disconformity?

- Sub-parallel strata on each side
- difficult to recognize
- Sedimentary rock above and below

What is the process of formation of disconformity?

1. Deposition of limestone (below sea level)
2. Erosion of limestone (presumably above sea level)
3. Deposition of sandstone
4. Tilting of whole package

What is a non-conformity?

- older metamorphic or igneous rocks below
- younger sedimentary rock above
- evidence of crustal movements
- inclusions can help identify these feature

What is the principle of correlation of rock layers?

- Relative dating can be applied to the local area
- We must correlate rock layers from one location to another
- Can be correlated using physical characteristics
- method can not easily link the rock sequences in separate continents
- fossils provide a method to correlate rock layers that are widely separated

What is the principal of fossil succession?

- distribution of fossils over time is not random or constant
- this allows for the cross referencing to reduce the age of a rock

What are index fossils?

- fossils present in a wide geographic range and short time span
- used for determining ages of rocks

What were some initial theories of the age of the earth?

1. James Usher (based on timing of bible) - 4004 B.C
2. James Hutton - no beginning and no end
3. John Joly (Based on how long it would take to make the sea salty for no salt) - 80-100 Ma
4. Lord Kelvin - estimated that

What was James Ushers age of the earth?

- 4004 B.C
- based timing on historical events recorded in the bible

What was James Hutton age of the earth?

- stated that the earth had no beginning nor end

What was John Joly age of the earth?

- estimated 80-100 Ma
- studied the amount of salt required to make the sea that salty
- assumed that salt wasn't being taken out and that the ocean wasn't already salty

What was Lord Kelvin age of the earth?

- Estimated 20-400 Ma
- Estimated the rate of which a sphere would cool by the conduction of heat
- Did not realize that the heat is transported by both convection and conduction
- Heat was also generated by radioactive decay

What is an element?

- A substance composed of atoms that all have the same properties

What is an Isotope?

- An element that behaves the same chemically but has different atomic mass numbers
-some isotopes are radioactive and decay

What is radioactive decay?

- The process where an unstable atomic nucleus is transformed into an atomic nucleus of a different element
- does not depend on molecule/compound or pressure or temperature
- Exponential process

How can we measure radioactivity?

- Measurements are made using a mass spectrometer
- vaporizes sample and accelerates through a magnet (heavier ions deflect less)

How does metamorphis affect radioactive decay?

- Metamorphism can 'reset' the radiometric rock

Where does radioactive dating work best?

- Works best in igneous rocks

What is an eon?

- Largest units of time

What is the sequence of eons?

(Old) Hadean - Archean - Proterozoic - Phanerozoic (New)

What is the order from the large to the small sequence of time divisions?

(Large) Eon - Era - Period - Epoch (Small)

Within the Phanerozoic eon, What is the sequence of eras?

(Old) Paleozoic - Mesozoic - Cenozoic (New)

What period is in the Paleozoic era?

- Periods which end in "IAN" are found in this era
- Permian
- Pennsylvanian
- Mississippian
- Devonian
- Silurian
- Ordovician
- Cambrian

What periods are found in the Mesozoic Era?

- Periods which end in "IC" or "OUS"
- Cretaceous
- Jurassic
- Triassic

What periods are found in the Cenozoic Era?

- Periods which end in "ENE" or "ARY"
- Quaternary
- Neogene
_Paleogene

What Eons comprise the Precambrian

- Hadean
- Archean
- Proterozoic

What was the time of the Hadean Era?

- 4567-4000 Ma

What was the time of the Archean Era?

- 4000-2500Ma

What was the time of the Proterozoic Era?

- 2500-541 Ma

What was the time of the Phanerozoic Era?

- 541-0 Ma

What was the time of the Paleozoic Era?

- 541 - 250 Ma

What was the time of the Mesozoic Era?

- 250- 65 Ma

What was the time of the Cenozoic Era?

- 65-0 Ma

What was the time for the Quaternary Period?

- 2.6-0 Ma

What was the time of the Neogene and Paleogene periods?

- 65 - 2.6 Ma

What occurred during the Hadean Eon?

- Magma ocean on early earth
- cooled to form solid rock at surface

What occurred during the Archean Eon?

- Oceans started to form
- plate tectonics different from modern
- Development of early single-celled organisms in oceans

What occurred in the Proterozoic Eon?

- First plants and animals
- Plate tectonics similar to those today
- Two supercontinents formed and broke up
- Snowball earth at the end

What occurred during the Phanerozoic Eon?

- Visible life
- Formation and break-up of Pangea

What happened during the Paleozoic Era?

- defined by appearance of animals with hard shells
- formation of Pangea

What happened during Mesozoic Era?

- Pangea begins to break up
- Dinosaurs and mammals
- Ended by mass extinction and volcanic activity

What happened during the Cenozoic Era?

- Development of mammals
- Break-up of Pangea

What is Dendrochronology?

- Age measured by the growth rings of trees

What is the history of rocks in Alberta during the Cambrian?

- layer of sandstone deposited, no geological history
- Ocean front location

What is the history of rocks in Alberta during the Devonian-Mississppian?

- Carbonates deposited (Leduc reefs) will become oil resivoirs
- Ocean-front location with passive margin

What is the history of rocks in Alberta during the Permain?

- Erosion when Alberta was a part of Pangea

What is the history of rocks in Alberta during the Cretaceous?

- West coast becomes a subduction zone
- Building of the rocky mountains
- Thick sediment basin across Alberta
- High sea levels

What is the history of rocks in Alberta during the Quaternary?

- Ice age
- Surface coved by glacial deposits

What is the history of rocks in Alberta today?

- continual erosion