315
See also: Alexander von Humboldt 130–35 ■ Charles Darwin 142–49 ■
Charles Keeling 294–95 ■ Lynn Margulis 300–01
D
uring the early 1960s,
a team was assembled
by NASA in Pasadena,
California, to think about how
to look for life on Mars. British
environmental scientist James
Lovelock was asked how he would
tackle the problem, which prompted
him to think about life on Earth.
Lovelock soon discovered a
range of necessary features for life.
All life on Earth depends on water.
The average surface temperature
must stay within 50–60°F (10–16°C)
for enough liquid water to be
present, and it has remained within
this range for 3.5 million years.
Cells require a constant level of
salinity and generally cannot
survive levels above 5 percent, and
ocean salinity has remained at
about 3.4 percent. Since oxygen
first appeared in the atmosphere,
about two billion years ago, its
concentration has remained close
to 20 percent. If it were to drop
below 16 percent, there would
not be enough to breathe—if it
rose to 25 percent, forest fires would
never go out.
The Gaia hypothesis
Lovelock suggested that the
entire planet makes up a single,
self-regulating, living entity,
which he called Gaia. The very
presence of life itself regulates
the temperature of the surface, the
concentration of oxygen, and
the chemical composition of the
oceans, optimizing conditions
for life. However, he warned that
human impact on the environment
may disrupt this delicate balance. ■
FUNDAMENTAL BUILDING BLOCKS
EARTH AND ALL ITS
LIFE FORMS MAKE
UP A SINGLE LIVING
ORGANISM CALLED GAIA
JAMES LOVELOCK (1919–)
IN CONTEXT
BRANCH
Biology
BEFORE
1805 Alexander von Humboldt
declares that nature can be
represented as one whole.
1859 Charles Darwin argues
that life forms are shaped by
their environment.
1866 German naturalist
Ernst Haeckel coins the
term ecology.
1935 British botanist Arthur
Tansley describes Earth’s life
forms, landscape, and climate
as a giant ecosystem.
AFTER
1970s Lynn Margulis
describes the symbiotic
relationship of microbes and
Earth’s atmosphere; she later
defines Gaia as a series of
interacting ecosystems.
1997 The Kyoto Protocol
sets targets for the reduction
of greenhouse gases.
Evolution is a tightly coupled
dance, with life and the
material environment as
partners. From the dance
emerges the entity Gaia.
James Lovelock