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was generated quickly and spontaneously, and this, some thousands
of years later (according to his published timescale), was doomed to
perish as the planet froze. To Buffon the planets of the solar system
were therefore broadly alike, and the kind of evolution of life and envi-
ronment on Earth was nothing special, but was repeated in general
outline among planets everywhere.
The Pioneer
A century after Buffon, the great Swedish chemist and polymath
Svante Arrhenius (1859-1927) considered the question again—only
by this time astronomical techniques had improved. Telescopes pro-
vided clearer pictures, and showed the existence of not just many
more stars but of galaxies too. Somewhat confusingly, these were
then called 'nebulae', while the dust clouds that we call nebulae today
were glimpsed as 'empty spots' that, some thought, might have been
due to 'opaque mist-formations' that blocked the starlight. Arrhen-
ius, presciently, regarded these 'mist-clouds' as the breeding ground
for new stars, and was aware too that the Milky Way was a spiral
'nebula' of enormous scale—his estimate of 100,000 light years being
not far off present estimates. The universe, by his day, had hence
become gigantic.
Furthermore, light from the stars and planets could be analysed to
give clues as to the chemistry of distant objects. Arrhenius knew,
therefore, of the abundance of hydrogen and helium in the universe,
and deduced that Mercury, like the Moon, had essentially no atmos-
phere—and no water. With Mars he was well aware that it changed its
appearance though time, and he knew of the large Martian polar ice
caps first glimpsed as light patches by the Italian-born French astron-
omer Giovanni Cassini in 1666. A hundred years later, the British
astronomer William Herschel (see Chapter 1) saw the southern ice cap
shrinking and expanding with the seasons, suggesting the presence of
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