Ch 12 Proterozoic Eon
Proterozoic Eon
Proterozoic Eon
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Early <strong>Proterozoic</strong> life<br />
• Even after the origin of eukaryotes, prokaryotes<br />
were dominant until about ~1.9 Ga—what<br />
happened then?<br />
• Build-up of atmospheric oxygen was achieved<br />
by ~1.9 Ga, as evidenced by decrease in banded<br />
iron formations and appearance of “red beds”<br />
(oxidized sediments)<br />
• O 2 combined with N 2 to form nitrates (NO 3 ),<br />
which acted as “fertilizer” to accelerate the<br />
evolution of eukaryotic algae<br />
Earth History, <strong>Ch</strong>. <strong>12</strong> 10
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