24. What is an argument that
shows that the emergence of
photosynthetic beings was
crucial for life to reach the
marine surface and later the
dry land?

Gap-fill exercise

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Ultraviolet radiation from the was
not disallowed to the surface of
the earth. Therefore the
development life on dry land even
near the aquatic was
impracticable. Probably the living
beings lived submerged deep water
to avoid by solar radiation.

Only the appearance of
photosynthetic and the later
filling the atmosphere with oxygen
by them the formation the
atmospheric ozone layer filters
ultraviolet radiation was .