1.11 Summary

Rocks are classified into three types according to how they were formed. Igneous rocks are formed by crystallisation from the molten state; sedimentary rocks are deposited at the Earth's surface from water, air or ice; and metamorphic rocks are rocks of any origin that have been subsequently transformed (metamorphosed) by heat and/or pressure, often several kilometres below the Earth's surface.

Rocks are generally either crystalline, i.e. formed of interlocking mineral crystals, or frag
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1.10 Changing sea-level

Sedimentary rocks reveal how environmental conditions in Britain's geological past were extremely different from those of the present day (in fact ‘Britain’, like the rest of the Earth's geography is transitory when viewed in terms of the very long span of geological time). As well as evidence from sedimentary rocks, recent landforms also indicate that in the more recent geological past (within the Quaternary Period), sea-level was not the same as it is at present.

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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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1.5.3 Sedimentary strata

We've seen that the detective work of piecing together a part of Earth's history from sedimentary rocks involves detailed investigation of rock samples, but this can give only a partial picture. On the larger scale of a rock exposure, there can be plenty for us to see and to interpret. Sedimentary rocks are usually found as layers referred to as strata (Author(s): The Open University

1.3 Minerals and rocks

To begin with, it is necessary to explain the meanings of the two terms ‘minerals’ and ‘rocks’.


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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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1.5.1 Light-gathering power

One of the key benefits of using a telescope is that it enables fainter objects to be detected than with the naked eye alone. The light-gathering power of a simple telescope used with an eyepiece is defined as

where Do is the diameter of the objec
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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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1.5.3 Summary of Section 1.5

  1. Some annual plants and insects can spend the winter at juvenile stages, such as seed, egg, larva or pupa. Butterflies in Britain display a variety of juvenile overwintering strategies.

  2. Migration often results in high mortality, but completion of the journey results in higher breeding success, due to increased availability of food and fewer competitors.

  3. Birds increase their body mass, sometimes by up to 50%, prior to migration. T
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1.5.1 Juvenile survival

For organisms that are able to complete their life cycles within a year there is the possibility of spending the winter in various juvenile stages. We have already considered annual plants, the adults of which may die before the onset of winter, with seed not germinating until the spring. Surviving the winter as seeds has the advantages that the seeds are robust, and because they have a low water content they are less affected by freezing temperatures. Disadvantages of this strategy include t
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1.2.5 Summary of Sections 1.1 and 1.2

  1. The majority of organisms are exposed to environmental fluctuations, including seasonal change in climate. In this unit, we focus on the effects of winter.

  2. Organisms have evolved a range of strategies to cope with winter. Thus this common environmental variable has led to a diversity of responses.

  3. The strategies for coping with winter can be considered with respect to different levels and types of explanation.

  4. Mol
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Acknowledgements

The content acknowledged below is Proprietary (see terms and conditions) and is used under licence.

Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit:

Figures

Figure 6a NASA Goddard Space Flight Center/COBE Science Working Group;

Figure 6b Courtesy of NASA/WMAP Science Team;

Figure 7 Courtesy of NOAO.

1. Join the 200,000 students currently studying with
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3: Work done against gravity – gravitational potential energy

So far we have only considered objects falling under gravity. Let's now consider the work done when we lift an object. In order to lift an object that has mass m, we have to apply an upward force mg to overcome the downward force of gravity. If this force raises the object through a height h, then the work done is:

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Introduction

From the moment that Galileo dropped two cannonballs of different sizes and weights from the top of the Leaning Tower of Pisa mankind has been fascinated by the impact of gravity. This unit looks at gravity, its impact on objects and how the energy involved in the movement of objects is dispersed or stored.

This unit is from our archive and is an adapted extract from How the universe works (S197) which is no longer taught by The Open University. If you want to study formally with us, yo
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1.5.5 Social Bookmarks

If you find you have a long unmanageable list of favourites/bookmarks you might like to try social bookmarks as an alternative.

Activity - What you need to know about Social Bookmarks

Read 7 things you should know about social
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1.5.4 The 5 Ds

If you don’t use a system at all, then you could suffer from the effects of information overload:

  • losing important information

  • wasting time on trying to find things

  • ending up with piles of physical and virtual stuff everywhere

One technique you might like to apply to your files (be they paper or electronic) is the 5Ds. Try applying these and see if you can reduce your information overload.


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1.5.3 Desktop search tools

Finding your paperwork or electronic files can be a problem. You may find that even if you do have some sort of filing system, your structure soon gets quite large with files in multiple locations, which can be hard to navigate. You may find yourself making arbitrary decisions about which folder to place a document in. It may make sense now but in the future, when you look where you think it should be, it’s not there.

At times like this you may resort to the search command from the Wi
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1.5.2 Ways of organizing yourself

How do you organize yourself?

Activity

Make a note of how you organise your:

  • emails

  • internet bookmarks or favorites

  • computer files

  • your h
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1.3.10 Choosing The Right Tool For The Job

Before searching it is always a good idea to check what the source you have chosen covers to make sure it will unearth information that matches your search need (you will notice that all the resources we’ve covered in this guide have short descriptions to enable you to decide which to use). Some of the decision makers, depending on the context of your search might be:

  • Does it have full text?

  • Does it cover the right subject?


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1.2.1 Planning Your Search

Your approach to searching will depend to a great extent on what kind of person you are. In an ideal world, when searching for information for a specific purpose, we would all find what exactly we were looking for at the first attempt, especially if we are in a hurry. However, it’s always a good idea to have some kind of plan when you are searching for information, if only to help you plan your time and make sure you find the information you need. If I was starting to search for material on
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