Geologic Time Scale Study Notes

Geologic Time Scale Overview

• Geologic Time Scale (GTS): A system of chronological dating that relates geological strata to time. It is used by geologists and other scientists to describe the timing and relationships of events in Earth's history.

Major Divisions of the Geologic Time Scale

• The Geologic Time Scale is divided into eons, eras, periods, epochs, and ages.

1. Eons

• Precambrian: Spanning approximately 4.5 billion years to 541 million years ago.

• Phanerozoic: Encompasses the last 541 million years and is further divided into three eras:

  • Paleozoic: 541 million years ago to 252 million years ago.

  • Mesozoic: 252 million years ago to 66 million years ago.

  • Cenozoic: 66 million years ago to present.

2. Eras Within the Phanerozoic Eon

A. Paleozoic Era (541 - 252 million years ago)

• Periods:

  • Cambrian (541 - 485 million years ago)

  • Ordovician (485 - 443 million years ago)

  • Silurian (443 - 419 million years ago)

    • Subdivisions:

      • Early, Middle, Late Silurian.

      • Epochs:

      • Llandovery, Wenlock, Ludlow, Pridoli.

  • Devonian (419 - 359 million years ago)

  • Carboniferous (359 - 299 million years ago)

    • Subdivisions:

      • Mississippian, Pennsylvanian.

  • Permian (299 - 252 million years ago)

B. Mesozoic Era (252 - 66 million years ago)

• Periods:

  • Triassic (252 - 201 million years ago)

    • Subdivisions: Early, Middle, Late Triassic.

  • Jurassic (201 - 145 million years ago)

    • Subdivisions: Early, Middle, Late Jurassic.

  • Cretaceous (145 - 66 million years ago)

    • Subdivisions: Early, Late Cretaceous.

C. Cenozoic Era (66 million years ago - Present)

• Periods:

  • Paleogene (66 - 23 million years ago)

    • Epochs: Paleocene, Eocene, Oligocene.

  • Neogene (23 - 2.6 million years ago)

    • Epochs: Miocene, Pliocene.

  • Quaternary (2.6 million years ago - Present)

    • Epochs: Pleistocene, Holocene.

3. Detailed Phanerozoic Time Frame

Cenozoic Era (Detailed Epochs)

• Paleogene Period:

  • Paleocene: 66.0 to 61.7 million years ago

  • Eocene: 61.7 to 56.0 million years ago

  • Oligocene: 56.0 to 33.9 million years ago

• Neogene Period:

  • Miocene: 23.04 to 5.33 million years ago

  • Pliocene: 5.33 to 2.58 million years ago

• Quaternary Period:

  • Pleistocene: 2.58 million to 11,700 years ago

  • Holocene: 11,700 years ago to present

Mesozoic Era (Detailed Periods)

• Triassic Period:

  • Early: 252 to 247 million years ago

  • Middle: 247 to 237 million years ago

  • Late: 237 to 201 million years ago

• Jurassic Period:

  • Early: 201 to 174 million years ago

  • Middle: 174 to 163 million years ago

  • Late: 163 to 145 million years ago

• Cretaceous Period:

  • Early: 145 to 100 million years ago

  • Late: 100 to 66 million years ago

Paleozoic Era (Detailed Periods)

• Cambrian Period: 541 - 485 million years ago

• Ordovician Period: 485 - 443 million years ago

• Silurian Period: 443 - 419 million years ago

• Devonian Period: 419 - 359 million years ago

• Carboniferous Period: 359 - 299 million years ago

  • Mississippi and Pennsylvanian Subdivisions

• Permian Period: 299 - 252 million years ago

4. Precambrian Era (Detailed Time Frame)

• Eon: 4.5 billion years ago to 541 million years ago

  • Hadean: Informal, up to 4 billion years ago

  • Archean: 4 billion to 2.5 billion years ago

  • Proterozoic: 2.5 billion to 541 million years ago

  • Eons Within Proterozoic:

    • Eoarchean, Paleoarchean, Mesoarchean, Neoarchean, Paleoproterozoic, Mesoproterozoic, Neoproterozoic.

5. Importance of Geologic Time Scale

• Applications: Understanding Earth's history, fossil record, and evolutionary biology.

• Connections to Natural Events: Key to determining geological events such as mass extinctions, plate tectonics, and climatic changes.

• Philosophical Implications: Raises questions about the origin of life, extinction events, and the future evolutionary path of Earth’s biological diversity.

Numerical and Statistical References

• Important Ages and Transitions in Geologic Time:

  • Cenozoic Era starts at 66 million years ago

  • Mesozoic Era spans from 252 million years ago to 66 million years ago

  • Paleozoic Era spans from 541 million years ago to 252 million years ago.