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7. Evolution and extinction
Dorrik Stow
in Oceans: A Very Short Introduction
7. Evolution and extinction Life is inextricably bound with the oceans, from its first origins to its blossoming into the rich variety we know today. The passage of life through the different eras of ocean history is marked by evolutionary divergence and episodes of mass extinction, when up to 80 per cent of the planet’s species were wiped out. Evolution has been painstakingly slow—from single-celled to multi-celled organisms, from asexual replication to sexual reproduction with associated mutations, and from soft-bodied creatures for which we have sparse fossil evidence to protective hard parts that are a thousand times easier to preserve.
1. What is special about Earth’s atmosphere?
Paul I. Palmer
in The Atmosphere: A Very Short Introduction
1. What is special about Earth’s atmosphere? Which of us haven’t occasionally been entranced by the perpetual movement of clouds or the majesty of lightning? Who hasn’t wondered why the sky is blue in the daytime, dark at night, and sometimes an explosion of colour at sunset? Or why most of Earth’s rainforests are located near the equator while most major deserts are located at thirty degrees north and south? But how many of us have pondered why Earth’s atmosphere is the way it is, what makes it special, and appreciated its many chemical and physical properties that we rely
1. The atmosphere
Storm Dunlop
in Weather: A Very Short Introduction
1. The atmosphere Box 1 Temperatures and differences in temperature To prevent confusion, meteorologists show actual temperatures by the use of the degree symbol (e.g. 20 °C) and differences in temperature by the abbreviation ‘deg.’ (e.g. 5 deg. C). Note that temperatures are also sometimes expressed in kelvins, named after William Thomson, 1st Baron Kelvin (1824–1907), the physicist, who first identified the need for an absolute thermometric scale. The scale is measured from absolute zero, at which all molecular motion ceases (–273.16 °C). A kelvin is a unit of heat, so temperatures given on the Kelvin scale (such as
4. Atmospheric composition
Paul I. Palmer
in The Atmosphere: A Very Short Introduction
4. Atmospheric composition Nitrogen, oxygen, and argon collectively represent more than 99.9 per cent of the air we breathe. The gases relevant to climate and human health that sometimes dominate the headlines are all described in that remaining 0.1 per cent of air. But Earth’s atmosphere hasn’t always had that composition—it is on at least its third distinctive atmosphere.
8. Scratching the surface with cosmogenic isotopes
Rob Ellam
in Isotopes: A Very Short Introduction
8. Scratching the surface with cosmogenic isotopes Cosmogenic ray interactions 14 C is produced in the Earth’s atmosphere by the interaction between nitrogen and cosmic ray neutrons that releases a free proton turning 14 7 N into 14 6 C in a process that we call an ‘n-p’ reaction, which can be characterized, using the shorthand of nuclear reactions, as: 14 N n , p 14 C . 14 C a ‘cosmogenic’ isotope. The half-life of 14 C is about 5,000 years, so we know that all the 14 C on Earth is either cosmogenic or
2. The circulation of the atmosphere
Storm Dunlop
in Weather: A Very Short Introduction
2. The circulation of the atmosphere 7. Edmond Halley’s 1686 map of the winds in the tropics.
4. Water in the atmosphere
Storm Dunlop
in Weather: A Very Short Introduction
4. Water in the atmosphere Box 4 Air doesn’t ‘hold’ water 2 ) and oxygen (O 2 ) molecules are present. For every molecule of water vapour (H 2 O) that is introduced in any given volume, one molecule of either nitrogen or oxygen is forced to leave. This leads to the initially apparently paradoxical situation, which many people have difficulty in believing, that humid air weighs less than dry air.
6. Our future atmosphere
Paul I. Palmer
in The Atmosphere: A Very Short Introduction
6. Our future atmosphere There is still much about Earth’s atmosphere we do not fully understand, which limits our ability to predict large-scale changes to the atmosphere. As Earth’s climate changes new scientific challenges will emerge that need to be addressed with new measurements and models. These challenges have implications for assessing the impact of future global economic growth and mitigating humanitarian risks. Here, I outline (some) future challenges we face.
4. Chemical broth
Dorrik Stow
in Oceans: A Very Short Introduction
4. Chemical broth The Earth is a single unity linked everywhere by oceans and seas. The remarkable properties of the simple water molecule have not only coloured the planet blue when viewed from outer space, but also allowed Earth to retain its hydrosphere and all its cycles, the seas to develop their saltiness and hierarchy of tiers, and life to develop and flourish. Water is a super-solvent, absorbing gases from the atmosphere and extracting salts from the land. About 3 billion tonnes of dissolved chemicals are delivered by rivers to the oceans each year, yet their concentration in seawater has
6. Ocean–climate nexus
Dorrik Stow
in Oceans: A Very Short Introduction
6. Ocean–climate nexus The oceans and atmosphere are intricately coupled. Together they control and express both the daily drama of Earth’s weather systems and the long-term changes in planetary climate. Winds drive the currents that redistribute heat across the face of the globe—a transfer of energy that is staggering in its enormity, and essential to the maintenance of a habitable world. But the climate is no more constant than its ocean regulator is simple. The natural state for Earth during most of its history has been one of warm (greenhouse) conditions. These have been sporadically interrupted by cold (icehouse) conditionsView:
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