Module 2-PPT

Earth's History and Geological Time Scale

Introduction

  • Overview of Earth's geological history, including methods to estimate age and define time periods.

Objectives

  • Understand techniques for dating rocks: relative dating and absolute dating.

  • Learn how these methods help classify geological time subdivisions.

  • Explore the role of marker fossils in defining geologic time.

Geological Time Scale Overview

Major Time Divisions

  • Eon: Broadest division of geological time, lasts up to a billion years.

  • Era: Subdivision of an eon, shorter time frame.

  • Period: Further subdivision within an era.

  • Epoch: Minor subdivision of geological periods.

Pre-Cambrian Eon

Definition

  • Known as the earliest eon before recognizable fossils, also called the Cryptozoic or "obscure life" Eon.

  • Divided into three eras: Hadean, Archean, Proterozoic.

Hadean Era (4.6 to 3.8 BYA)

  • Origin of the term "Hadean" from Hades, implying chaos.

  • Notable event: An asteroid possibly struck early Earth, forming the Moon.

Archean Era (3.8 to 2.5 BYA)

  • Characterized by water-covered Earth; small islands began forming.

  • Dominance of unicellular prokaryotes, such as bacteria and cyanobacteria.

  • Introduction of cyanobacteria led to atmospheric oxygenation.

Proterozoic Era (2.5 BY to 542 MYA)

  • Longest era in Earth’s history.

  • Marked by significant geological and biological changes, including further atmosphere oxygenation.

Phanerozoic Eon

Definition

  • The next eon after Pre-Cambrian, known for complex organisms.

Divisions of Phanerozoic Eon

  • Paleozoic Era: Early marine life and complex organisms emerged.

    • Notable periods: Cambrian (hard-shelled invertebrates), Ordovician (first vertebrates).

  • Mesozoic Era: Age of reptiles and dinosaurs; includes Triassic, Jurassic, and Cretaceous periods.

  • Cenozoic Era: Known as the "Era of New Life".

Geological Dating Techniques

Relative Dating

  • Determines the relative age of rocks based on their positions.

  • Principle of Superposition: In undisturbed strata, older layers are at the bottom.

  • Principle of Original Horizontality: Layers of sediments are originally deposited horizontally.

  • Cross-cutting Relationships: If a rock is cut by another geologic feature, that feature is younger.

Absolute Dating

  • Provides the exact age of an object through the ratio of parent to daughter isotopes (e.g., radioactive decay).

  • Radioactive Decay: The transformation of unstable isotopes into stable ones.

  • Half-life: Time taken for half of a radioactive substance to decay (e.g., Carbon-14 = 5,730 years).

Fossils and Index Fossils

Definition and Types

  • Fossils: Preserved remains or traces of ancient organisms.

  • Index Fossils: Specific fossils that define and identify geologic periods.

Examples of Fossils

  • Ammonites and other ancient marine organisms through various geological periods.

Conclusion

  • Understanding geological time and fossil records is essential for piecing together Earth’s history, indicating the evolution of life and changes in the environment.