Geology: A Complete Introduction

Book Preface

‘The green earth, say you? That is a mighty matter of legend, though you tread it under the light of day!’* Although taken from a work of fiction, about a fictional situation, those words may be taken as the theme for this book. The Earth is a mighty matter of legend. Its origin and the events that have taken place in its history do indeed form a grand and epic tale. Moreover, various parts of this story have been interpreted in many ways; some of these are contradictory, and others are now thought to be untrue.

I should also point out that some of what geoscientists now believe fairly firmly will undoubtedly turn out to be wrong, or only partly correct. However, I think it is fair to claim that we understand very well (for the purpose of an introductory book such as this) most of the processes that shape the materials at, and immediately beneath, the Earth’s surface.

Probably, what we lack most is a fully developed understanding of the interdependence of all these processes. For example, over geological timescales, measured in tens of thousands or millions of years, the Earth’s climate has changed many times. It is changing today, and the consensus among scientists is that humans are to blame for the current rapid rate of global warming because of the gases we have released into the atmosphere, notably carbon dioxide through burning coal and oil and various industrial processes. However, other factors drive climate change, too. These include changes in the tilt of the Earth’s axis and slight variations in the shape of its orbit, minor fluctuations in the energy output of the Sun, the slow drift of the continents that forces readjustment of the ocean circulation pattern, the rise and fall of mountain belts, catastrophes such as giant volcanic eruptions and impacts by asteroids and comets, and even the emergence and evolution of life itself. All these factors have played a role in driving the temperature and climate of the Earth in one direction or another. Just how significant human-induced global warming will be in the grand scheme of things remains to be seen, though I think it is likely to impact severely on ecosystems and human cultures in many parts of the globe.

Climate, in turn, influences how fast and in what manner rock that is exposed at the surface becomes worn away, and where it is redeposited as sediment. Thus, all the factors listed above must leave some kind of imprint on the history of our planet, as revealed by a study of the rocks. The complexities are boundless, but nevertheless we now have a reasonably complete understanding of how the Earth as a whole functions.

People may become interested in geology, which is the scientific study of the Earth, for a variety of reasons. Many are intrigued by fossils, or pebbles that they pick up on the beach, and wonder what they mean. Others want to know more about earthquakes and volcanoes reported in the news, and whether such events are likely in their own neighbourhood. Some may be curious about where the oil comes from that powers their car, or what their house bricks are made of. And some are just overawed by the grandeur of the mountains or impressed by the pictures of the Earth and of other Earth-like bodies sent back by space probes, and decide that they want to find out more.

Whatever your own reason for opening this book, I hope you will find what you want. I have tried to address all these concerns, and others. Most chapters aim to help you understand a particular type of geological process. You don’t have to read these chapters in the sequence in which they are printed, but it will be easier if you do. This is because I have attempted to build up the use of terminology (geology is riddled with strange-sounding words!) in a coherent fashion. Notable exceptions to the process-oriented approach are the next chapter (which is a descriptive account of the composition of the Earth) and the final chapter (which deals with fieldwork and the simple equipment you will find useful if you decide to go and look at rocks and fossils for yourself). At the end of the book is a glossary, where the most important terms (introduced in bold in the text) are defined.