Cataclysmic events drove the first five mass extinctions in Earth’s history. An asteroid ended the age of the dinosaurs. Volcanic eruptions may have caused the Great Dying, which wiped out much of the earth's marine life.
Altogether, the five mass extinctions caused 75 percent of the planet’s life to die out. The sixth mass extinction may now be beginning — and we're the cause of this one.
Over the last several centuries we have constantly burned fossil fuels, like oil, coal and natural gas. In the process, we've changed the climate for other species. Humans use more than half of the planet’s unfrozen land for cities and logging or food. Our takeover has destroyed the natural habitats of animals and plants.
Humans have existed for 200,000 years on Earth. Biologists (study life) and paleoecologists (who study ancient ecosystems) estimate that humans have driven roughly 1,000 species extinct. Early man helped hunt the biggest animals — woolly mammoths, giant kangaroos and giant sloths — to extinction. Since 1500, we have killed off at least 322 types of animals. The passenger pigeon, the Tasmanian tiger and, most recently, the baiji, a freshwater dolphin in China are all gone forever.