According to the geologic time scale, Earth has already experienced five mass extinctions. The most famous mass extinction came from space, but the biggest might have been because of carbon dioxide. Cataclysms, whether the asteroid that ended the dinosaurs' reign or the volcanism that may have caused the Great Dying, drove the first five mass extinctions in Earth's history, in which 75% of more of the planet's life died out. But what's happening now?
"Anthropocene defaunation," or the sixth mass extinction that's happening to the planet now is because of us - humans. Scientists can't be sure of the current die-off rate, perhaps because much of it is happening to beetles and other insects that are notoriously overlooked. But according to a study in Science, the total number of such invertebrates fell by half over the past 35 years while the human population doubled.
So what do we do about this? There are several methods for going about conservation legislation. The most successful method involves protecting keystone species - those species such as wolves and ochre sea stars that hold together entire ecosystems because of the roles that they play. Conservation programs for these species, which can include protection laws and reintroduction processes, are potentially more important than protection of those cute charismatic megafauna like elephants, tigers, and polar bears. (Although protection of such animals can also be an umbrella protection for many other not-as-cute species like in the case of pandas and certain endangered ferns!)
Sources: Scientific American