Biologists studying plant life in the prehistoric rainforest by utilizing samples of ancient ice and fossilized evidence of biological processes found that most of the plants removed an astonishingly small amount of carbon dioxide from the atmosphere. One biologist found that a certain tree currently found in the rainforest absorbs carbon dioxide from the atmosphere at a greater rate than any tree on the planet. The biologist hypothesized that the prevalence of this tree in the prehistoric rainforest accounts for the other plants' failure to remove larger amounts of carbon dioxide from the atmosphere. Which of the following, if true, would most seriously undermine the biologist's hypothesis? ['The amount of carbon dioxide in the atmosphere has remained steady since prehistoric times.', 'The trees currently found in the rainforest are largely hybrids and a product of crossbreeding that occurred in the late twentieth century.', 'The plant life in the prehistoric rainforest also contained larger amounts of chlorophyll than modern day plants.', 'The prehistoric humans did not seem to be adversely affected by the amount of carbon dioxide in the atmosphere.']