What evidence indicates oxygen started accumulating in the atmosphere and oceans during the Proterozoic? How does
this evidence support the accumulation of oxygen? What will be an ideal response?
When oxygen is not present, iron is soluble in water. In the presence of oxygen, iron is highly
reactive and forms iron-oxide minerals, such as hematite and magnetite. These rustlike oxides
does not readily dissolves in water; therefore, precipitates out as a solid. About 2.3-2.5 bya
banded iron formations appear in the rock record. These formed during episodes of oxygen
accumulation in the oceans. Chert and iron oxides precipitated out until all of the dissolved
oxygen was consumed, then deposited.
Once all the iron had precipitated out of the oceans, oxygen began to accumulate in the
atmosphere. This is evident from the formation of red beds. In the presence of oxygen, iron
will oxidize. Evidence of oxygenation on land occurs after 2.3 bya.
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A) 80% B) 60% C) 40% D) 20%
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A) hydrograph B) aquagraph C) flow chart D) precipitation graph
The moist subtropical climate experiences abundant rainfall with a winter maximum.
a. true b. false
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