Study Guide for The Dynamic EarthThe Dynamic Earth This book is about the Earth’s climate and the various factors that cause it to change. The Video Band most related to it is ‘Did Tibet Cool the Earth?’. The book is assessed in TMA 02. (Note that there are self-assessment questions in the Multiple Choice Question Booklet. You should complete these as you study the text and they will also be useful for revision of the Course.) Chapter 1 An hospitable planet Why is the Earth hospitable to life while its immediate neighbours in the Solar System are not? To begin to answer this question, we consider how the distribution of incoming solar energy over the surface of the Earth is determined by its particular orbit around the Sun and the tilt of its axis of rotation. Having established the cause of the seasons, we look at variations in incoming solar radiation over time-scales of thousands of years – the Milankovich cycles. Finally, we examine how the solar radiation reaching the Earth’s surface varies over decades, in response to changes in solar activity. This idea of change occurring simultaneously over a number of different time-scales, in response to several different driving mechanisms or ‘forcing factors’, is one that recurs throughout. Chapter 2 Keeping the Earth habitable In the second chapter, we begin to bring in the other factors which modify the Sun’s influence. The global distribution of temperature is not determined simply by the Earth’s radiation budget, but is greatly modified by the behaviour of its fluid envelopes – the atmosphere and the ocean – which in turn are affected directly and indirectly by the position, shape and topography of the continents. Together, solar radiation (light and heat), water supply and the availability of nutrients determine the distribution of primary production (plant growth) and hence the distribution of other organisms. We look briefly at two examples of the interaction of different parts of the Earth system: the El Niño– Southern Oscillation phenomenon, and the monsoon of southern Asia (which will reappear in Chapter 6). Chapter 3 The carbon cycle Life on this planet is based on the chemistry of carbon, and the CO2 concentration in the atmosphere is an important influence on global temperatures; it should not be surprising, therefore, that the cycling of carbon between atmosphere, biosphere, hydrosphere and lithosphere is an important theme of this book, as well as others in the Earth and Life series. Cycling of carbon occurs on three time-scales: the short term (the terrestrial carbon cycle, dominated by photosynthesis and respiration); the intermediate term (the marine carbon cycle); and the long term (the geological carbon cycle). We end the chapter by considering the long-term controls on atmospheric CO2 , and also look at how humans are causing enhanced greenhouse warming by short-circuiting the geological carbon cycle Chapter 4 Volcanism and the Earth system We begin with a summary of why volcanoes are found where they are, in relation to plate boundaries. In the short term, the component of volcanic emissions that has the biggest impact on climate is sulfur dioxide, through its tendency to form sulfuric acid aerosols, which are cloud condensation nuclei. By examining the impacts of relatively recent eruptions, we attempt to quantify the effects of large eruptions known only from the geological record. Over the long term, it is the emission of CO2 that is important – and we explore possible links between eruptions of flood basalts, climate change and mass extinctions. Chapter 5 Plate tectonics, carbon and climate Here, we look at the factors that affect climate over very long time-scales, particularly the changing configuration of continents and oceans, and resulting changes in current patterns. Intimately related to these are changes in ice-cover and in sea-level (between and within Ice Ages), in weathering and in the preservation and accumulation of organic and inorganic carbon. Chapter 6 Tibet, the Himalayas and the Arabian Sea The Dynamic Earth concludes with a case-study centred on the uplift of the Tibetan Plateau and the Himalayas – an event that resulted from lithospheric plate movements, yet eventually involved all components of the Earth system – the atmosphere, ocean and biosphere, as well as the lithosphere. It is thought that – largely through its effect on the strength of the South-West Monsoon – the uplift of Tibet may have altered global chemical weathering rates, and hence climate. We look at various methods that have been used to determine the timing of the uplift of Tibet, as well as the evidence for climate change over the same period. In the process, we examine the implications for two hypotheses linking atmospheric CO2 , global weathering rates and climate – the ‘BLAG’ model and that proposed by Raymo and Ruddiman. Required background and the most difficult sections This is a long book, but rest assured that you will already have encountered many of the concepts in Origins of Earth and Life. Furthermore, many of those that are new will reappear later in the Course, so you will have a chance to consolidate your understanding. If you have studied Discovering Science (S103) or the Science Foundation Course (S102), and have the background needed for the previous book, you should be able to cope with the material in this book. The most difficult parts are probably those highlighted below: Chapter 1 The Milankovich cycles (Section 1.2). Chapter 2 The Earth’s radiation budget (Section 2.3.1). You may also find that bringing together strands from different disciplines is challenging. Note also that you will not be expected to reproduce the arguments relating to the cause of the Coriolis effect, only appreciate the implications of its existence for winds and currents. Chapter 3 The marine carbon cycle, particularly the carbonate system and the role of weathering (Sections 3.3.2 and 3.3.3). Chapter 4 We think you will find this chapter straightforward. There are quite a lot of calculations (including those relating to ‘radiative forcing’ of aerosols) but they are all relatively easy, although they may look daunting. Chapter 5 The use of q 18 O for studying changes in ice-volume and hence sea-level ( Section 5.2). Attempting to bring together the various strands linking plate tectonics, sea-level and climate is also fairly challenging. Note that some of the material in this chapter will come up again in the Set Book and/or its Study Guide. Chapter 6 The use of q 13 C for studying the abundance of organic carbon (Section 6.2.2). Note, however, that you have already encountered this topic in Origins of Earth and Life and it will come up again in Atmosphere, Earth and Life and in Evolving Life and the Earth . Calculations involving the use of Sr-isotopes (Boxes 6.2 and 6.3) are much more straightforward than they may appear at first sight. A word about time-scales In this book, as in some others in the Earth and Life series, you will see a number of different conventions used to indicate time on graphs. In particular, some plots show time increasing from left to right, and others from right to left. This has arisen because different disciplines within the Earth Sciences have developed their own ways of showing data. Workers who study cores of deep-sea sediment or soil, for example, generally show data corresponding to the top of the core (i.e. the most recent deposits) on the left-hand side (or at the top, if the plot is displayed vertically). By contrast, a plot showing (say) the increase in atmospheric CO2 concentrations over recent years, or changes in sea-level, that we might want to extrapolate, is always shown with time increasing towards the right. The use of the two conventions should not be a problem, but until you are familiar with the geological time-scale, as shown on the Course Bookmark, you might find it useful, on first encountering a graph, to check the direction in which time increases. Video material Video Band 3: ‘Did Tibet Cool the Earth?’ This programme is best viewed so as to complement Chapter 6, as it highlights the interactions between mountain uplift, weathering, atmospheric CO2 concentrations and climate. The impetus for the programme is the hypothesis, first advanced by two American scientists, Maureen Raymo and Bill Ruddiman, that uplift of the Tibetan Plateau was ultimately responsible for the onset of the current Ice Age. Whether it was the cause is not resolved, but the programme provides a valuable illustration of the links between the different components of the Earth system – as well as a chance to see the spectacular scenery of western Tibet. Website Read the following sections on the S269 website: Dynamic Earth – Topics TMAs Course News Other Resources Supplementary Materials Copyright © 2003 The Open University SUP 74299 4 Back to S269 |