Geologic Time - Deep Time

Frameworks for Geologic Time

*Earth = 4.6 billion yrs. old, but recorded human history ~5000 yrs

= 2 ways of dealing with time.…

 A. Absolute/Numerical Time

 B. Relative Time

Geologic Time Scale
• Concepts of relative and absolute time combined to create =>

• Geologic Time Scale

• Units of time

• Eon, Era, Period

Relative Time
• Relative Dating = sequence of events through time: establishing order in with rocks are deposited and subsequently deformed and altered.......…
 - based on the principle of uniformitarianism

• Steno's and Hutton's Principles:

1. Principle of original horizontality

2.  Principle of original continuity

Layers originally continuous throughout a region => erosion
 

3.  Principle of superposition

Oldest layers on the bottom => younger layers near the top
Relative Time - Principles
4. law of cross-cutting relationships
 
5. law of inclusions

6. Law of Floral/Faunal Succession

=> different groups of fossils succeed one another in the geologic record in a definite and recognizable order.....…the evolutionary clock

  William “strata” Smith
 

=> conformable beds or strata = relative continuous deposition => no periods of erosion or nondeposition (time not represented by strata).......

=> unconformity = the result of periods of erosion and nondeposition = missing time......

1.  Disconformity

 layered rocks over layered rocks…….erosion and nondeposition

2.  Angular unconformity

layered rocks over tilted rocks………..

3.  Nonconformity

 layered rocks over crystalline rocks……..

• Recognition = Crucial => time not represented by rock

Unconformities - influence on the rock record
Application - Relative Time
- using the principles of relative time to reconstruct the geologic history of a complex area

Reconstructing Geologic History
 - describe rocks
 - establish sequence of events - principles & fossils
 - interpret environments = sedimentary facies

Lateral and Vertical Relationship of Facies (Time & Space)

 => Stratigraphy
=> How does this history recorded in these rocks relate to the region and the rest of the world? - Correlation
 

Stratigraphic Terminology -

Lithostratigraphy - Units = Group, Formation, Member, Bed

Correlation of stratigraphic units

Types

 lithostratigraphic
correlation

 similar rock types
 Formations
Event Correlation

uses marker beds

ash beds/bentonites
Correlation => Types

Guide Fossils
Properties

 occurs during a short interval in time

 is easy to recognize and is common

 lived in many different places…..

After correlation
 - can reconstruct regional changes in environments, sea level, and climate