ÜDS-Fen 2003-1 Soru=75

One understands from the passage that the great extinction that occurred at the end of the Permianperiod ----.

Air-starved soil could have been a key player in the
largest extinction ever to strike Earth. The claim
follows the discovery of a rare mineral in ancient soil
collected from Antarctica. The extinction, at the end
of the Permian period 250 million years ago, wiped
out virtually all marine life and some 70 per cent of
land animals. But the reason for the extinction,
which preceded the rise of the dinosaurs, has been
a longstanding puzzle. Now a team of geologists
think they have found what could be a major factor
in the extinction. They collected fossilized soil
samples that formed in Antarctica just after the
Permian period ended. The soil contained noduleshaped
minerals that have been identified as
berthierine. This iron-rich mineral forms only in
environments where oxygen is scarce. So, if the
oxygen levels in the soil were low enough to allow
berthierine to form, then it follows that the soil would
not have been able to support plant life. Such
intolerably low levels of oxygen would be enough to
kill the plants off completely.