1. Unit: 2 Historical Geology
Earth Systems 3209
Unit: 2 Historical Geology
Reference:
Chapters 6, 8; Appendix A & B

2. Life Forms and Geologic Time
Unit 2: Topic 4.1
Life Forms and Geologic Time
Focus on . . .
outlining the divisions of the geologic time scale.
recognizing that the Phanerozoic Eon represents the emergence of the first visible life in rocks.

3. Divisions of Geologic Time
Geologic Timescale
Divisions of Geologic Time
Eon, Era, Period, Epoch
Largest span of time
Smallest span of time

4. Geologic Timescale Names of the Eons Phanerozoic (“visible life”)
The most recent Eon, began about 540 million years ago
Proterozoic
Archean
Hadean
The oldest Eon

5. Geologic Timescale Eras of the Phanerozoic Eon:
Cenozoic (“Recent life”)
Mesozoic (“Middle life”)
Paleozoic (“Ancient life”)
Eras are subdivided into Periods.
Periods are subdivided into Epochs.

6. Geologic Timescale Precambrian (4600 – 540 million years ago)
Not divided into smaller time units because the events are not known in great detail, due to age, erosion and lack of fossil life forms.
Little direct evidence of fossils, due to lack of hard body parts.
As the Precambrian came to a close, the fossil record showed multi-cellular organisms which made it possible for the evolution of more complex plants and animals in the Paleozoic era.
Fossil evidence include; - algae, bacteria, and traces of soft body organisms.

7. Geologic Timescale Paleozoic Era (540 – 245 million years ago)
The beginning of the Paleozoic Era is marked by the first appearance of life-forms which had hard body parts.
Abundant fossils in the Paleozoic allowed scientist to construct a detailed time scale for the last 13% of geologic time.
Paleozoic time can be divided as; Early Paleozoic (Cambrian & Ordovician) Middle Paleozoic (Silurian & Devonian) Late Paleozoic (Carboniferous & Permian).

8. Geologic Timescale Mesozoic Era (245 – 66 million years ago)
Consist of three periods of time;
Triassic
Jurassic
Cretaceous
Reptiles were the dominant life form during this Era.

9. Geologic Timescale Cenozoic Era (66million years ago – Present)
Consist of two periods of time;
Tertiary
Quaternary
Mammals were the dominant life form during this Era.

10. Example 1: Which is the shortest unit of geologic time?
(A) Eon (B) Epoch (C) Era (D) Period
What part of the geologic time scale makes up the largest percentage of Earth’s history?
(A) Cenozoic (B) Devonian
(C) Paleozoic (D) Precambrian
Precambrian time consist of which three Eons?
(A) Archean, Hadean, and Phanerozoic
(B) Hadean, Phanerozoic, and Proterozoic
(C) Phanerozoic, Archean, and Proterozoic
(D) Proterozoic, Archean, and Hadean

11. Your Turn . . .
Take the time and complete the following questions (Solutions to follow)
Questions:
Which represents the greatest expanse of geologic time?
(A) Eon (B) Epoch (C) Era (D) Period
Which Eon dated back 570 million years and has a meaning of “visible life”?
(A) Archean (B) Hadean (C) Phanerozoic (D)Proterozoic
Which time span would least likely contain fossil evidence? (A) Cenozoic (B) Mesozoic (C) Paleozoic (D) Precambrian

12. Solutions . . .
Questions:
Which represents the greatest expanse of geologic time?
(A) Eon (B) Epoch (C) Era (D) Period
Which Eon dated back 570 million years and has a meaning of “visible life”?
(A) Archean (B) Hadean (C) Phanerozoic (D)Proterozoic
Which time span would least likely contain fossil evidence? (A) Cenozoic (B) Mesozoic (C) Paleozoic (D) Precambrian

13. Summary . . . Overview of Points covered: Timescale is divided into:
4 Eons
3 Eras
11 Periods
7 Epochs

14. Summary . . Overview of Points covered: Precambrian (87%)
The Geologic timescale is divided into:
4 Eons
3 Eras
11 Periods
Ages
Phanerozoic (13%)
Cenozoic
Quaternary
Mammals
Tertiary
Mesozoic
Cretaceous
Reptiles
Jurassic
Triassic
Paleozoic
Permian
Amphibians
Carboniferous
Devonian
Fishes
Silurian
Ordivician
Invertebrates
Cambrian
Proterozoic
Precambrian (87%)
Archean
Hadean
Summary . .
Overview of Points covered: