Formation and Dating of Rocks

Question 1

Explain Stratification

Answer 1

General term for layering of sedimentary rocks. It serves as a reflection of changing conditions during deposition where every strata or layer represents an interval of time where conditions have remained uniform. A change in color can reflect differences in grain size and/or composition.

Question 2

What is the difference between “Relative Dating” and “Absolute Dating”?

Answer 2

• Relative Dating cannot tell us how long ago something took place, only that it followed one event and preceded another.
  
  • It means that relative dating establishes what rock is older than what rock.
• Absolute Dating refers to dates that are expressed in millions and billions of years.
  
  • It establishes how old the rock actually is (eg. This rock is over a million years now.).

Question 3

What are the 6 principles of Relative Dating?

Answer 3

• Principle of Superposition
• Principle of Original Horizontality
• Principle of Lateral Continuity
• Principle of Cross-Cutting Relationship
• Principle of Inclusions
• Unconformities

Question 4

Who headed the Principle of Superposition?

Answer 4

Nicolas Steno, a Danish anatomist, geologist, and priest (1638-1686)..

Question 5

Explain Principle of Superposition

Answer 5

• The principle simply states that in an undeformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below.
• The younger rock is on top, while the older rocks slips below.

Question 6

Explain Principle of Original Horizontally.

Answer 6

• It states that layers of sediment are generally deposited in a horizontal position.
• Rocks in a horizontal position are considered undisturbed, while rocks that are slant were affected by deposition.

Question 7

Explain Principle of Lateral Continuity

Answer 7

• It refers to the fact that sedimentary beds originate as continuous layers that extend in all directions until they eventually grade into a different type of sediment.
• Rock layers were once connected to each other, but something big shookt them.

Question 8

Explain Principle of Cross-Cutting Relationship and the connection between it and dikes.

Answer 8

• It states that geologic features that cut across rocks must form after the rocks they cut through.
• Primarily, Igneous rocks (dikes) were the ones who intruded.
• Dikes are usually younger because they are intrusions, therefore they disturbed the older rocks.

Question 9

Explain Principle of Inclusions

Answer 9

• Inclusions are fragments of one rock unit that have been enclosed within another.
• For example, when a magma intrudes a surround rock blocks of that rocks may be incorporated to the magma making them the inclusions.
• Inclusions aka Xenoliths.

Question 10

Explain Unconformities

Answer 10

An unconformity represents a long period during which deposition ceased, erosion removed previously formed rocks, and then deposition resumed.