During the Silurian,the Oxygen Gas Concentration in the Atmosphere Is

question 7

Multiple Choice

During the Silurian,the oxygen gas concentration in the atmosphere is postulated to have reached an amount equivalent to more than 10 percent of its present-day concentration.Thus,nearly all lethal ultraviolet radiation was unable to reach the Earth's surface,making dry land available for newly evolved forms.Which of the following major events in the evolution of animals and plants probably occurred at this time?

• A)The amphibians developed watertight skins and eggs.
• B)The crayfish become the first land organisms.
• C)The first major groups of seed plants appeared.
• D)Primitive bryophytes and fern-like plants appeared.

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