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
1.6.2 Metamorphic recrystallisation To consider metamorphic recrystallisation at its simplest, let's begin by imagining a sedimentary rock composed entirely of quartz grains – a quartz sandstone. Sandstone is a sedimentary rock and so has a fragmental texture (see Figure 7b). When it is subjected to high temperature and high pressure n
1.6.1 Causes of metamorphism What natural process could cause a rock to be heated? Heating can be caused when hot magma is intruded into a cool rock. On the o
Answer
1.4 The formation of igneous rocks Igneous rocks are defined as having solidified from a molten state, either inside the Earth or on the surface at volcanoes.
1.3.2 Rocks Any naturally formed solid assemblage of mineral grains can be described as a rock. The mineral grains may be fragments of crystals or intact crystals and their size can range from a few micrometres (1 micrometre = 10−6m) to a few centimetres. A rock may consist of one type of mineral but more usually it consists of several minerals. Rocks can be classified according to the way in which the grains are arranged, although the identity of the minerals present (for example, the rock
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;
References
8 Websites for further information: Primers on drug addiction: For general in
5.2.1 Free radicals and ageing Free radicals are physical species (i.e. Author(s):
4.7 Ageing brains: hope for the future Due to the enormous progress in the field of molecular and cell biology, new avenues in brain research have opened up.
2.2 Specific issues in addiction The term ‘addiction’ carries a number of different meanings. The word is generally used with reference to drugs (e.g. heroin, nicotine, alcohol), where a person is described as being ‘dependent on’ or ‘addicted to’ a substance. Also, substances are described as ‘addictive’ or ‘non-addictive’, implying that addiction is an intrinsic property of the substance. Some people are addicted to food. Given that food is necessary, in what sense is
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
2.1.2 Diffraction and interference of light When light, or indeed any type of wave, passes through a narrow aperture, it will spread out on the other side. This is the phenomenon of diffraction. For example Figure 17 shows the diffraction of water waves in a device called a ripple tank. The extent to which waves are diffracted depends on the size of the aperture rel
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
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
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
References 1.2.1 The molecular level It is common knowledge that the freezing point of pure water is 0°C. Often, however, the temperature of water can fall below 0°C without it freezing, for two reasons: Any solvent containing a dissolved substance has a lower freezing point than when pure, which is why the sea freezes at a lower temperature than clean freshwater. The occurrence of supercooling, the phenomenon by which a fluid remains liquid at a temperature below Introduction In this unit, we study one aspect of the fluctuating nature of an organism's environment. We consider how organisms living in a temperate climate, such as that in Britain, are adapted to cope with winter. You will see that there is much diversity of adaptations among organisms, with different species coping with the demands of a fluctuating environment in quite different ways. As cyclic variations are a widespread feature of environments, the range of adaptations to them is an important sourc 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.
