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3.5 A new life

There is a common belief that life begins at the moment of conception, i.e. when a sperm fuses with an egg. This is a step forward from past years, when life was alleged to start at the time of ‘quickening’, i.e. when a woman could feel her fetus moving inside her. However, both these opinions suffer from an underlying falsehood: that life ‘begins’ at all. Life is a continuum; gametes are produced by living parents, and fuse to produce new living individuals, but unfused gametes are n
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Learning outcomes

After completing this unit you should be able to:

  • Define and use, or recognize definitions and applications of, each of the terms printed in bold in the text.

  • Explain the scientific basis for the main methods of contraception. (Question 1)

  • List the factors affecting fertilization. (Questions 2 and 5)

  • Describe with the help of diagrams the early stages of embryonic development. (Question 3)

  • <
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3.4.7 Induced earthquakes

Some reservoirs cause earthquakes to occur. This is perhaps not so surprising, as earthquakes are caused by stress in rocks, and the addition of a large mass of water in a reservoir on top of the rocks at the Earth's surface stresses the rocks and can trigger an earthquake. Not all reservoirs induce earthquakes: it is in general only the larger reservoirs, or the deeper ones (over 100m deep), and only if the reservoir is built in an earthquake area, releasing stress already stored in t
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Introduction

We have seen that where precipitation reaches the ground, some runs off the surface into streams and rivers and some of it infiltrates, passing through the soil. Water that reaches the water table to become groundwater may eventually re-emerge at the surface as springs where the water table intersects the surface. Almost all streams and rivers have springs or seepages as their ultimate source, or are fed by them at various points along their courses.

This unit is from our archive and is
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3 Summary

Power output from wind turbines is proportional to the area swept by their blades, and to the cube of wind speed. The narrow range of useable wind speeds restricts the areas where wind energy can be exploited.

Wind power has great potential, but has three main drawbacks. Output depends on intermittent wind speeds, irregular distribution of suitable wind speeds, and occupancy of large areas of land.


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Except for third party materials and otherwise stated (see terms and conditions), this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence

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1 Solar energy

The Sun will radiate energy until it ceases thermonuclear fusion, in around 5 billion years. The solar power that enters the Earth's system is 1.1 × 105TW (0.3 × 105 TW to atmospheric heating and 0.8 × 105 TW absorbed at the surface – Figure 1). This is equivalent to a global e
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3 Hot dry rock (HDR) fields

Heat flow through some parts of the continental crust can be well above normal locally because the underlying rocks contain abnormally high concentrations of uranium, thorium and potassium, which generate considerable heat. To add significantly to surface heat flow and thereby create high-temperature anomalies at shallow depths requires a large volume of such radioactive rocks. This condition is satisfied by some, but not all, granitic igneous intrusions, whose original magma became ch
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Learning outcomes

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

  • explain the principles that underlie the ability of geothermal energy to deliver useable energy;

  • outline the technologies that are used to harness the power of geothermal energy;

  • discuss the positive and negative aspects of geothermal energy in relation to natural and human aspects of the environment.


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6 Summary

Nuclear power generation results from fission of uranium isotopes when bombarded by neutrons. Conventional burner reactors require relatively scarce uranium-235, whereas fast breeder reactors (which have not yet been developed on any significant scale) would exploit more abundant uranium-238.

In the early 21st century over 400 nuclear — mainly burner — reactors produced 16% of global electricity demand.

The UK played a leading role in nuclear power developments during the 1950
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4.5 Geological criteria for safe radioactive waste disposal

Even in the best of circumstances, containers such as the one shown in Figure 19 will survive for only 100–1000 years, although the glass itself may inhibit the migration of radioactive isotopes for a further 1000 years. So, in view of the long decay times (Author(s): The Open University

4.2 Reactor safety: the Chernobyl incident

By far the worst nuclear reactor accident took place on 26 April 1986 when one of four 1 GW reactors at Chernobyl in the Ukraine released a radioactive cloud over Europe (Figure 17). (See S278 video clips document.) The build-up to this accident has been related to a series of complex chemical reactions induced
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Introduction

The transformation of radioactive uranium and, in some instances, thorium isotopes provides vastly more energy per unit mass of fuel than any other energy source, except nuclear fusion, and therein lies its greatest attraction.

The potential of nuclear fuels for energy production became a reality when the first experimental atomic pile, built by Enrico Fermi and Léo Szilárd at the University of Chicago, began functioning in December 1942. That led to the manufacture of fissionable mat
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6 Summary

  1. Waterlogged organic matter accumulates in deltaic, coastal barrier or raised mires to form peat. Coal forms by the compaction and decomposition of peat. Chemical changes imposed by increasing temperature and pressure over time determine the coal rank.

  2. Coalfields can be classified as either exposed or concealed, depending on whether or not the coal-bearing rocks are hidden by younger strata. In most coalfields, mining commenced in the shallower
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5 Coal production in the UK early in the 21st century

This section examines the UK's coal industry in a little more detail, to see how the complex interplay of location, economics and politics has led to the rapid demise of an industry that was once at the heart of the UK's economy.

Figure 38 shows production and consumption figures for coal mined in the UK since 1945 a
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3.1 Environmental aspects of coal mining

Coal produced by both types of mining is used either to fuel electricity generation or for industrial and domestic heating, both of which result in atmospheric pollution, but here we are concerned with direct environmental impact on the land. Surface and underground mining operations cause significantly different environmental problems. Those that surround surface mining are common to any large quarrying operation: sterilization of the land and restoration of quarry sites; dust; and noise whi
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2.3.4 Geophysical methods — borehole logging

If a core is not recovered from a borehole, another way to assess the types of rock that it penetrates is to measure their physical properties. Mounting a string of electronic instruments behind the drill bit most conveniently does this: it allows the properties of the rock to be monitored as the borehole is drilled. An alternative is to lower instruments down the completed borehole by cable; hence the name wireline logging.

Such logging measures several physical properties of th
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2.2 Winning coal in former times

Coal was probably first used as a fuel by early Chinese civilizations, and there is evidence for coal working in the UK since Roman times. However, early approaches to mining were limited by the available technology, and left much of the coal behind.

At first, coal was dug from seams exposed at the surface in shallow excavations into valley sides that followed the coal seam. The amount of coal that could be extracted from these trenches and from adits (short horizontal tunnels) w
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1.6 Impurities in coal

Coal rank reflects the maturity of a coal, but another variable is the ratio of combustible organic matter to inorganic impurities found within the coal. As discussed earlier, impurities result mainly from clay minerals washed into the mire prior to its eventual burial. In addition, some impurities are formed from the plant material itself during coalification.

These inorganic impurities are non-combustible and therefore leave an inert residue or ash after coal combustion. High-a
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