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?

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The high oxygen levels during the Silurian made dry land available for newly evolved forms, leading to the appearance of primitive bryophytes and fern-like plants. The development of watertight skins and eggs in amphibians and the emergence of seed plants occurred later in the Devonian period. Crayfish, as arthropods, were already present in the oceans and did not become the first land organisms.

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