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

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.

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

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

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.

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.

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).

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.

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.

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

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

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

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

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: