Study Guide for The Dynamic Earth

The 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

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.


Read the following sections on the S269 website:

Dynamic Earth – Topics
Course News
Other Resources
Supplementary Materials

Copyright © 2003 The Open University SUP 74299 4

Back to S269