There are 2 Major Eons
represent 87% of
From 4.5 Byrs to
544 Myrs ago
and Cenozoic Eras
544 Myrs to present
Existed 544 Myrs to
248 Myrs ago
248 Myrs to 65
Great Time of
65 Myrs ago to
It is the here and now
Law of Original Horizontality
Law of Superposition
Law of Original Continuity
Law of Faunal Assemblages
Law of Faunal Succession
Law of Crosscutting Relationships
Law of Incusions
Law of Unconformities
Relative Time vs. Absolute Age
Relative Age is determined using a
Geologic Column. How do rock strata or
layers relate to each other.
Absolute Age is determined through
radioactive dating and gives an
“absolute” age of the rock.
Creating A Geologic Column
We must obey the
previous stated laws
Using the laws we can
reconstruct geologic Obey
events by constructing
a geologic column
Law of Original Horizontality: All
sediments laid down in water are
horizontal or near horizontal.
Law of Superposition: Undisturbed
sedimentary rocks are older at the
bottom of the formation and younger at
The Laws Continued
Law of Original Continuity:
Sedimentary rocks exist laterally until
the thin or pinch out at their margins.
Law of Faunal Assemblages: Plants
and Animals of the same age will exist
together within the rocks.
Law of Faunal Succession: Different
geologic formations of different ages
will have different fauna.
Law of Crosscutting Relationships: Any
rock cutting another must be younger
that the one it cuts.
Last Two Laws
Law of Inclusions: Fragments of another
rock in another rock are older than the
rock they are in.
Law of Unconformities: Rocks above the
unconformity are younger than the
ones below it.