The reduction in oxygen levels in Earth’s atmosphere toward the end of the Cretaceous period may have been caused by volcanic activity. Volcanic activity could have increased, modifying the relative amounts of atmospheric gases, such as carbon dioxide and oxygen. In turn, this would influence the evolution of life on the planet. This is known as the “Pelé hypothesis,” after the Polynesian goddess of volcanoes.
Many people today are concerned that global warming—evidenced by such phenomena as melting ice caps—will lead to species extinctions, including, possibly, our own. Scientists speculate that environmental changes may have also led to the dinosaurs’ extinction (iStock).