Dorrik Stow
in
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.
Paul I. Palmer
in
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
Geoff Cottrell
A Very Short Introduction
Paul I. Palmer
A Very Short Introduction
Storm Dunlop
A Very Short Introduction
Storm Dunlop
in
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
Paul I. Palmer
in
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.
