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2.3.1 Soil pH

pH (a measure of acidity or alkalinity) is an important environmental factor, particularly in soils. Soil is derived partly from accumulated decaying vegetation and partly from broken up fragments of the underlying rocks. Soil pH is determined by both these components and also by the water that fills the spaces between solid soil particles.

How might you expect the pH of soil overlying limestone (or chalk, which is a particular form of limestone) to compare with that of soil overlying s
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2.3 Two factors affecting the distribution of organisms

We will illustrate some of the complexities of interpreting ecological field data by looking at two sets of environmental factors, soil pH and salinity, desiccation and biotic interactions on sea-shores.


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2.1 Introduction

Ecology is usually defined as the study of organisms in their environments. In its broadest sense this definition includes the way we, the human species (Homo sapiens), interact with and use the environment. However, in the sense in which most ecologists work, ecological studies are limited to studies
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1.9 The rock cycle

As you are reading this, rocks are being formed and destroyed on the Earth. Rocks are being heated and squeezed to form new metamorphic rocks; other rocks are melting to form magmas, which eventually cool and solidify as new igneous rocks; and the processes of weathering, erosion, transport and deposition are generating new sediments. The continuous action of rock-forming processes means that (given time) any rock in the Earth's crust will become transformed into new types of rock and that th
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1.8.3 Explaining the observations

Having made and reviewed our observations, we are now in a position to interpret them – why are the rocks the way they are? The sedimentary strata that we see in Figure 16 were likely to have been deposited in essentially horizontal layers, so why is one set tilted and the other horizontal? To answer
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1.8.2 Interpretation of a geological exposure

We now want to make use of the observations obtained by sketching the exposure, and it is useful to start by briefly summarising the features seen. First of all, you probably noticed the large boulder in the foreground of Figure 16 (which has been attached below for ease of access). Where did this boul
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1.8.1 Making and using field sketches

How do we start to make sense of a rock exposure? Drawing a sketch is one of the best ways to start, as it forces you to notice many aspects of the exposure. It also helps you to build up a picture of which aspects are significant and which are incidental or even irrelevant to a geological study. The aim of a field sketch is that it provides a record of your observations (along with notes taken at the same time, and also perhaps a photograph to record details). A sketch is complementary to a
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1.7 Interlude

Now that we have covered the features found in igneous, sedimentary and metamorphic rocks, and seen how these features can be explained by the processes that formed the rocks, here is a useful point at which to have a break before continuing with the next section. Before returning, you might like to see for yourself what types of rock you can find in your area. Can you identify their texture, or spot any fossils? Surfaces that haven't been obscured by grime or lichens are by far the best, as
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Learning outcomes

By the end of this unit you should be able to:

  • explain the difference between a mineral and a rock;

  • describe the textural differences between igneous, sedimentary and metamorphic rocks;

  • account for these differences in terms of the processes that produce these rocks;

  • classify igneous rocks according to their grain size and mineralogical composition;

  • recognise the difference between a body fossil and a trace fossil;

    <
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Introduction

This unit is an adapted extract from the course Practising science (SXR103)

This unit introduces you to the types of activities undertaken by students of the earth sciences and ecology. You will learn how data is collected and analysed.


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2.1.3 Reflective diffraction gratings

Although the above description of diffraction has been in terms of light passing through a series of slits in a (transmission) diffraction grating, the type of grating which is currently most common in astronomy is a reflective diffraction grating or reflection grating. This again exploits the wave properties of light, in this case by making adjacent sections of a wavefront travel extra distances as it is reflected off a non-uniform surface. The non-uniform surface is actually a
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2.1.1 Prisms and the refraction of light

The simplest way to disperse light is to use a prism. When light enters a prism, it is no longer travelling in a vacuum, and its speed decreases. If the incident wavefront is travelling at an angle to the surface of the prism, which is easy to arrange because of its angled faces, then the propagation of the part of the wavefront in the prism is retarded, thus bending the wavefront and changing its direction of propagation through the prism (Author(s): The Open University

1.7 Summary of Section 1 and questions

  • Converging lenses or mirrors cause parallel beams of light to be brought to a focus at the focal point, situated at a distance of one focal length beyond the lens or one focal length in front of the mirror. Diverging lenses or mirrors cause parallel beams of light to diverge as if emanating from the focal point of the lens or mirror. Light paths are reversible, so a converging lens or mirror may also act as a collimator and
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1.1 A milestone in the advancement of astronomy

Unaided human eyes, well as they may serve the needs of everyday life, are not very suitable for detailed astronomical observation. First, the eye has a limited sensitivity. A distant source of light, such as a star, will not be seen at all unless the intensity of light from it reaching your eye is above the sensitivity threshold of the retina. Second, the ability of the eye to distinguish fine detail is limited by the finite physical size of the detectors on the retina and by the small apert
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References

Baker, J. M. R. (1992) Body condition and tail height in great crested newts, Triturus cristatus, Animal Behaviour, 43, pp. 157–159.
Bronson, F. H. (1987) Environmental regulation of reproduction in rodents. In: Psychobiology of Reproductive Behavior, D. Crews (ed.), Prentice Hall, New Jersey. p. 209.
Hedenstrom, A. and Alerstam, T. (1992) Climbing perfo
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1.8 Primordial nucleosynthesis

Time: 100 s to 1000 s

Temperature: 109 K to 3 × 108 K

Energy: 300 keV to 100 keV

As the temperature continued to decrease, protons and neutrons were able to combine to make light nuclei. This marked the beginning of the period referred to as the era of primordial nucleosynthesis (which literally means ‘making nuclei’). The first such reaction to become energetically favoured was that of a single proton and neutron comb
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1.7 The hadron era

Time: 10−5 s to 100 s

Temperature: 3 × 1012 K to 109 K

Energy: 1 GeV to 300 keV

From the time that the temperature fell to about 3 × 1012 K, at about 10−5 s after the Big Bang, stable baryons (protons and neutrons) began to form from the up and down quarks that remained after the annihilation of matter and antimatter.

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1.6 The quark-lepton era (contd)

The next stage of the story is to look at how and when the original mixture of all types of quark and lepton that were present when the Universe was 10−11 s old, gave rise to the Universe today, which seems to be dominated by protons, neutrons and electrons.

Question 8

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Acknowledgements

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Unit Image

Calum Davidson

All other materials included in this unit are derived from content originated at the Open University.

1. Join the 200,000 students currently studying withAuthor(s): The Open University

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