Planet Earth: about this book

This book is about a planet, the Earth, which happens to be the one which we humans inhabit and depend on for every aspect of our existence. Humans have had ideas about the Earth^[1] from the earliest times, but in the early 21st century, studying the Earth is especially important. For centuries, western study of the Earth has been focussed on what we, as humans, can find within it for our benefit. Those things are important:— it’s still true that all the objects that we use in everyday life are either grown or mined. If you are reading this book the old fashioned way, on paper, its material has mostly been grown as plants, and converted to wood-pulp for paper, but if you are reading it on a computer, tablet, or phone, then most of its components have been mined from the solid Earth, the Geosphere. Increasingly, we are becoming aware of the costs of these activities, especially as the products we use in our everyday lives are returned, not just to the Geosphere but also to the Atmosphere, the Hydrosphere, and the Biosphere.  This awareness has contributed an urgency to understanding how the Earth works, which is essential if we are to even begin to solve the many environmental problems facing humanity.

Spheres

What do these terms — Atmosphere, Hydrosphere, Biosphere, Geosphere^[2] — mean, exactly?  The Atmosphere is an envelope of gases, mostly nitrogen, but also oxygen, carbon dioxide, and water vapour, that forms the outer part of our planet.  The Hydrosphere includes all the liquid water that exists as a discontinuous shell, mostly below the Atmosphere and above the Geosphere, forming oceans, lakes, rivers, and groundwater. What about ice and glaciers? We usually treat them as part of the Hydrosphere, but some recognize a separate Cryosphere that includes the Earth’s glaciers. (It’s even possible to think of glaciers as part of the Geosphere, because solid ice behaves like rock in many ways.) The Geosphere is the mostly solid Earth that exists “beneath our feet” and beneath the ocean floor. Outer parts of the Geosphere consist of rocks composed mainly of solid chemical substances called minerals. The inner part of the Geosphere (the core) consists of metal, mostly in a liquid state. The Biosphere refers to all the living things on Earth. Physically, living things exist within the Atmosphere, the Hydrosphere, and the outer parts of the Geosphere (especially in the mixture of rock, water, and living things we call soil). The Biosphere is therefore mixed with the other spheres, but living things operate as such a distinctive system, and are so important to the planet, that it’s useful to give them a sphere of their own. Some recognize an Anthroposphere consisting of all the members of our human species and our constructions on the face of the Geosphere. Others prefer to regard humans as one part of the Biosphere, as this emphasizes our interactions and dependence on other living things. As we shall see, humans have existed for only a tiny fraction (about a tenth of a percent) of the time that life has existed on Earth. One of the things we hope this book will give you is a perspective on this enormous length of time and on humanity’s place on Earth.

Earth Systems Science

In western science courses, the spheres of the Earth have usually been the subjects of separate introductory courses with titles like Atmospheric Science, Oceanography, Biogeography, Paleontology, Geology, and Geophysics. However, the spheres are all open systems – that is, they trade both energy and material with their neighbours. Traditional knowledge systems have long recognized this by treating the Earth more as an organic whole than as separate parts. Earth systems science seeks to emphasize the links between the spheres in the study of the Earth.

This approach has obvious benefits, especially if we are to understand the impact that we, as humans (and part of the Biosphere), have on the rest of the planet. However, it also has disadvantages – there is a lot to cover! As a result, any course like this one has to leave out some of the detail that has been covered in introductory courses in the past. Some of your instructors may find this uncomfortable! For example, a geologist who learned a long list of important minerals and rock types at university may feel that the coverage in this book is disappointingly superficial. Similarly, an atmospheric scientist may feel that explaining atmospheric dynamics without calculus is a ‘dumbed down’ approach.

We believe that the approach taken here is important in making the vast range of Earth systems science accessible to a broad audience, including not just future scientists, but also future teachers, communicators, and public policy makers; you are the people who will have the task of bringing a better understanding of the Earth to the next generation. This approach is also valuable if you choose to go on to more detailed study of the Earth, to take further courses in subjects like geophysics, geography, atmospheric science, or paleontology, A broad introduction to our planet is the best foundation for more detailed study in more advanced courses and programs that focus more systematically on a single sphere.

Using this book

Most introductory texts in Earth science begin with the solid Earth, the Geosphere, introducing the many chemical substances (minerals) that it contains, and the numerous ways these are combined to make rocks. They then show how geologic time is measured, and continue with a look at the processes that have operated over geologic time, including those in the Atmosphere, Hydrosphere, and Biosphere, to produce the materials we see in the solid Earth.

This book is different. After a short introduction to what Earth scientists do, it begins with a tour of the Solar System, the only system we deal with that is more or less self-contained: it receives very little matter or energy from the rest of the universe. We look particularly at the flow of energy from the Sun to the Earth, which is critical to understanding the Earth’s climate. We then approach the Earth “outside-in” starting with the Atmosphere and Hydrosphere, because their compositions are relatively simple.  Two gases, nitrogen and oxygen, make up about 99% of the dry atmosphere, while the hydrosphere is over 96% water. These two spheres have a huge impact on the Biosphere, covered next, but conversely the Biosphere has also caused enormous changes in the Atmosphere and the Geosphere over the history of the Earth. Finally we examine the Geosphere itself, emphasizing the processes that produce the huge diversity of materials that we see in the Earth’s crust. We use a simplified approach to the materials of the Geosphere (rocks and minerals), dealing only with the largest groups, in contrast to the longer lists typical of introductory geology texts. We then examine the resources that humans exploit within the Geosphere, before returning to examine the impact of those activities on Earth’s climate. In many textbooks, climate is treated as a topic within the study of the Atmosphere. However, climate change is so bound up with the Geosphere, Hydrosphere, and Biosphere that we prefer to treat it as a topic in itself, drawing together themes encountered in the study of all the “spheres”.

This approach is not “cast in stone” (no pun intended)! The chapters are planned, as far as possible, to be self-contained documents which instructors may choose to use in any order. Because of the diverse audience in our classes, we have included some basic principles of numerical representation, matter and energy. University students entering science programs may well be familiar with this material already, but we hope that other students will find this useful. Basic principles of physics and chemistry are covered qualitatively, without much mathematics, with the intent of making the scientific study of the Earth as accessible as possible.

We use the following typographical conventions for key terms and concepts:

• Text like this is used for terms that are explained, or will eventually be explained, in the glossary of terms.
• Italic bold text is used to add emphasis for concepts that are important for understanding what follows.
• Bold italic text is used for the first part of a figure caption, explaining the content of the figure, and also for mathematical statements when they occupy a whole line of text.
• Italic plain text is also used for the names of people, for the names of species and genera like Tyrannosaurus rex and Homo sapiens, and for place names that are more local than continents, like Newfoundland or Papua New Guinea. Sources of illustrations are also shown in italic plain text.
• Text like this is used for hyperlinks, or future hyperlinks, either to other portions of the online text (excluding glossary entries) or to external web sources.

Because this text is in some sense a living document, and is stored on a computer, it’s possible for us to make changes as we become aware of things that need updating. The book has been in use while being developed. During this period we have marked text subject to change using the following markers. We plan to continue with updates as the need arises.

• —Placeholder for future section
• –Outline text only
• -+Mix of outline and completed text
• -Text mostly completed; needs diagrams
• +Text and diagrams mostly completed
• Unmarked chapter headings are mostly complete
• <angle brackets mark placeholders for figures or content that we plan to add>

Acknowledgments

Much of this book was written, in lands of the Indigenous people of what is now Canada, particularly in Treaty 6 and Métis territory, and in Mi’kma’ki, the unceded territory of the Mi’kmaq. Many of the examples described come from these and other Indigenous territories worldwide. We respect and acknowledge the connection of Indigenous people with the landscape that we study, and strive for a better relationship between all the peoples of the Earth and their planet.

We acknowledge contributions, through writing, slide decks, and discussions, of current and former instructors of EAS 100 and EAS 201 at the University of Alberta, including, but not limited to, Daniel Alessi, David Chesterman, Robert Creaser, Murray Gingras, Britta Jensen, Jeff Kavanaugh, Kurt Konhauser, Robert Luth, and Alex Wolfe.

We owe a debt to the textbook “Blue Planet”, 2nd and 3rd editions, by Brian Skinner, Barbara Murck, Stephen Porter and Alex Botkin. That textbook was influential on the design of the course EAS 100 on which this current text is in turn based, and we gratefully acknowledge its influence.

Finally, we acknowledge the thousands of people who have posted images under Creative Commons licenses, and into the public domain, in locations such as Wikipedia and Wikimedia Commons. Without these images a free textbook like this would be almost impossible to produce. If, when reading this book, you have appreciated these images, we encourage you to contribute a small part of the money you have saved (compared with the cost of a commercial textbook) to the Wikimedia foundation at https://wikimediafoundation.org/