- (E) Earth’s primitive forests first appeared around 300 million years ago
during the Carboniferous Period. Before then, the atmosphere held far more
CO 2 but concentrations declined throughout the Carboniferous Period (359
to 299 million years ago during the late Paleozoic Era) as plants flourished
and absorbed more and more CO 2 from the atmosphere through
photosynthesis, creating carbon sinks (coal, oil, etc.). During the
Carboniferous Period, the atmosphere became greatly depleted of CO 2
(declining from about 2,500 ppm to 350 ppm) so that by the end of the
Carboniferous Period the atmosphere was less favorable to plant life and
plant growth slowed. Today, CO 2 concentrations are approximately 380
ppm (0.038% of our atmosphere). The Arctic is feeling the effects of
increases in average global air temperatures the most with average
temperatures in Alaska, western Canada, and eastern Russia rising at twice
the rate of the global average.
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