Question 12 of 20 Select the best answer for the question
12. When did oxygen levels start to decline from 35 percent down to today's levels?
O A. During the Permian eriod
> O B. Before the Siluran period
C. After the Triassic period
Oo. Ater the Caroonferous period
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After the Carboniferous period

Explanation:

The oxygen levels start to decline from 35 percent down to today's levels "After the Carboniferous period." This is the period of about 298 million years ago after 60 million years of Carboniferous period which began around 358 million years ago. It was characterized by dense and swampy forests, which led to large deposits of peat.