When did oxygen levels start to decline from 35 percent down to today's levels? a. before the silurian period b. after the triassic period c. during the permian eriod d. after the carboniferous period

The oxygen levels on Earth were about 30-35% higher during the Carboniferous. That contributed to the enormous insects that evolved during that geological period. So if the oxygen level was at its peak during the Carboniferous, it only went in one direction after—> down. So the answer could only be D. After the Carboniferous period.

This is what i did 45-5=4040÷4=10so there are 10 white marbles but am not sure is just a question that am not sure