The Big Five mass extinctions occurred in the last half-billion years. Those events were caused climate change, an intense ice age, volcanoes, and the asteroid strike that obliterated the dinosaurs.
The Sixth Mass Extinction event, also called the Holocene extinction, is the ongoing extinction event of species during the present Holocene epoch. The large number of extinctions spans numerous families of plants and animals including mammals, birds, amphibians and reptiles. With widespread degradation of highly biodiverse habitats such as coral reefs and rainforest, as well as other areas, the vast majority are thought to be undocumented. The present rate of extinction may be up to 140,000 species per year.
The Sixth mass extinction event is anthropogenic, that is 99% of currently threatened species are at risk from human activities. Human activities contribute to species extinction in many ways:
- we bring in invasive species
- we change the climate very rapidly
- we change the chemistry of the oceans
- we change the surface of the planet
- we cut down forests
- we plant mono-culture agriculture
- we use chemicals that are damage species (i.e. neonics and bees)
- we overfish
- extractive industries dump environmental toxins that pollute local food source.
It is estimated that as many as three-quarters of animal species could be extinct within several human lifetimes.