Feb. 28, 2013 — A new model suggests that inhospitable
hydrodgen-sulphide rich waters could have delayed the spread of
complex life forms in ancient oceans. The research, published
online this week in the journal Nature Communications, considers
the composition of the oceans 550-700 million years ago and
shows that oxygen-poor toxic conditions, which may have delayed
the establishment of complex life, were controlled by the
biological availability of nitrogen. In contrast to modern
oceans, data from ancient rocks indicates that the deep oceans
of the early Earth contained little oxygen, and flipped between
an iron-rich state and a toxic hydrogen-sulphide-rich state. The
latter toxic sulphidic state is caused by bacteria that survive
in low oxygen and low nitrate conditions. The study shows how
bacteria using nitrate in their metabolism would have displaced
the less energetically efficient bacteria that produce sulphide
-- meaning that the presence of nitrate in the oceans prevented
build-up of the toxic sulph