Passage III
Forest fires require oxygen (O2) to burn. Figure 1 shows the number of paleowildfires (large forest fires known from the rock record) for each 10-million-year interval of the Mesozoic era (250-65 million years ago, mya). Figure 1 also shows a model of the percent O2 by volume (%O2 ) in Earth's atmosphere from 250 mya to 70 mya.
To study how %O2 affects burning, scientists attempted to ignite 7 samples of each of 4 different materials, 1 sample at a time, in a chamber. For each set of samples of the same material, the initial %O2 in the chamber ranged from 12% to 18%. Figure 2 shows, for each sample that ignited, the duration of the sample's flame.
Figures adapted from C. M. Belcher and J. C. McElwain, "Limits for Combustion in Low O2, Redefine Paleoatmospheric Predictions for the Mesozoic." ©2008 by American Association for the Advancement of Science.
14. The %O2 in Earth's atmosphere today is about 21. According to Figure 1, at which of the following times during the Mesozoic era was the %O2 in Earth's atmosphere closest to the %O2 in Earth's atmosphere today?
Your Answer is
Correct Answer is F
Explanation
Look at figure1, find the line representing oxygen, see which oxygen corresponding to the option time is closest to 21%, and find that it is 250mya