Life of the Oceans - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 131

32
28
24
20
16
12
8
4
0

14

0

12

20

10

40

8

60
Te mperature (°C)

6

80

pH

4

100

2

120

fig. 11. Not too hot, not too cold, not too salty, not too acid. The envelope
of life on Earth constrained by temperature, pH, and salinity. The figure
shows the physical parameters of life on Earth through geological time and
including the present. Life can exist in environments that are hostile for most
living organisms today (for example, hot springs or acid mine waters).
However, early life may have had to contend with such regimes across the
whole of Earth.

water vapour, carbon dioxide, and nitrogen. They lived in a world
where the oceans were saturated in ferrous iron but bereft of oxygen.
In such settings, organisms used a variety of means to generate their
energ y.
Many Archaea are chemoautotrophic, and use energy pathways
that are based on inorganic compounds such as ferrous iron, hydro-
gen sulphide, sulphur, and hydrogen to fix carbon dioxide. Ferrous
iron in particular was a ready supply of energy for microbes emerging
into the ancient oceans. In modern oceans, ferrous iron is scavenged
from water by free oxygen to form insoluble ferric iron (rust), and this