Several hypotheses exist to explain the gradual cooling experience following the PETM. These include (Select only those that apply. Making incorrect selections will decrease your score).
a. Extensive erosion removing ₂ from the atmosphere following the uplift of the Himalayan Mountains and Tibetan Plateau
b. Asteroid impact following the PETM caused wildfires which removed tremendous amounts of carbon as the forests died and turned to ash sediment.
c. An solar sunspot cycle that made the infrared radiation from the Sun less intense
d. The die off of Arctic ferns removed massive amounts of carbon as they died and fell to the bottom of the Arctic oceans.