Geological History – Lesson Summary

This is a lesson summary. The full lesson can be viewed by purchasing an online course subscription.

Learning Objective

In this lesson we will learn how the study of rock strata reveals information about Earth’s geological and biological history. We will also learn how Earth history is represented by the geological time scale.

Learning Outcomes

By the end of this lesson you will be able to:

  • Explain what is meant by the term ‘geological history’.
  • Define ‘stratigraphy’ and describe its main principles.
  • Describe what index fossils are and explain how they are used to date rock strata.
  • Distinguish between relative and absolute dating.
  • Describe radiometric dating, with examples.
  • Discuss how the study of rock strata can reveal information about past geological and biological events, with examples.
  • Describe the geological time scale.
  • Identify the four eons in geological history and describe some geological and biological events that they are characterised by.

 
geological history online science lesson contents

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Lesson Topics

1 | Earth’s Geological History

2 | Stratigraphy

3 | Principles of Stratigraphy

4 | Index Fossils

5 | Geochronology

6 | Historical Information Stored in Rock Strata

7 | The Geological Time Scale

8 | The Precambrian

9 | The Phanerozoic

10 | Summary

Lesson Summary

  • Geological history refers to how Earth has changed since its formation.
  • Stratigraphy is the study of rock strata to gain information about past geological and biological events.
  • Chronostratigraphy is the application of stratigraphic principles to the relative dating of rock strata, geological events and fossils. These principles include:
  • Original horizontality – sedimentary rocks are formed in horizontal layers.
  • Superposition – a sedimentary rock layer is younger than a layer that lies below it and older than a layer that lies above it.
  • Cross-cutting relationships – a geological feature that cuts across a rock layer is younger than the rock layer it cuts across.
  • Inclusion – fragments of rock that are embedded in another type of rock are older than the rock they are embedded in.
  • Biological succession – sedimentary rock layers contain distinct sets of fossils specific to the period during which they formed.
  • Index fossils are fossils used to correlate the ages of rock strata in different locations.
  • Geochronology is the use of radiometric dating for absolute dating of rocks and fossils.
  • Radiometric dating determines the age of an object by measuring the relative amounts of radioisotopes in a sample.
  • The study of rocks and fossils can reveal information about Earth’s geological and biological history, including: tectonic and volcanic activity, geographic and climatic changes, evolution and extinction events.
  • The geological time scale is a timeline consisting of intervals in Earth’s history that correspond with major geological and biological events.
  • It is subdivided into eons, eras, periods, epochs and ages.
  • The four eons are the Hadean, Archean, Proterozoic and Phanerozoic.
  • The first three eons are collectively known as the Precambrian.
  • The Phanerozoic Eon is divided into the Palaeozoic, Mesozoic and Cenozoic eras.

 
geological time spiral

(Image: USGS, Wikimedia Commons)

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