When the dinosaurs and two-thirds of all other plant and animal species died out suddenly 65 million years ago, it was the fifth mass extinction in history. A majority of scientists think that we are now in the midst of the sixth mass extinction. At the current rate of die-off, nearly 20 percent of all species on Earth will become extinct within 30 years. As we pollute the air and water, and destroy the species-rich rainforest, are we signing our own death warrant?