fusion: Stars are powered for most of their lives by the fusion of hydrogen
atoms into helium atoms, as a result of which vast amounts of energy are
released; source of the power of hydrogen bombs.
Gaia: The Greek goddess of the Earth; the name was used by James Lovelock
to describe the linked actions of all life forms on the surface of the Earth,
which for some purposes can be regarded as a single, vast organism that has
lived and evolved for almost 4 billion years; as Lovelock has argued, today
human activity may be inÀ icting signi¿ cant damage on Gaia, though he also
argues that Gaia may prove resilient enough to survive and outlast us.
Galapagos Islands: An archipelago of 19 islands in the Paci¿ c Ocean,
owned today by Ecuador and visited by Darwin for ¿ ve weeks in 1835; the
many tiny variations he observed between the species on different islands
helped crystallize his ideas on natural selection.
galaxies: Large “societies” of stars, held together by their mutual
gravitational pull.
global history: Studies of world history since the linking of the world into a
single system in the 15th century of the Modern era.
global warming: The observed increase in global average temperatures that
is almost certainly due mainly to the rapid increase in the amounts of carbon
dioxide in the atmosphere caused by the massive use of fossil fuels in the last
two centuries.
globalization: The increasing interlinking of different regions of the world
since 1492.
GNP: A standard measure of economic production; a widely calculated
measure, for which there are even estimates reaching several centuries into
the past. However, because it is based on market prices, it can tell little about
nonmarket production or about the ecological costs of production.