A mass extinction event, also known as an extinction pulse, is a rapid and widespread decrease in biodiversity. A typical mass extinction event occurs when 75% or more of all species become extinct within a relatively short period of time (usually less than 2 million years). The most famous mass extinction event was the Cretaceous–Paleogene (K–Pg) event that occurred 66 million years ago and resulted in the demise of the dinosaurs.
There have been five major mass extinction events in Earth’s history, but there is some debate as to whether or not we are currently experiencing a sixth mass extinction event. The “Big Five” mass extinctions are:
# The Ordovician–Silurian Extinction Event: 439 Mya
# The Late Devonian Extinction Event: 359 Mya
# The Permian–Triassic Extinction Event: 251 Mya
# The Triassic–Jurassic Extinction Event: 200 Mya
# The Cretaceous–Paleogene Extinction Event: 66 Mya Of these five events, the K-Pg event had the greatest impact on biodiversity, causing the loss of over half of all species on Earth.
There is evidence that we may be currently experiencing a sixth mass extinction event. This potential sixth mass extinction has been dubbed the Holocene or Anthropocene extinction because it is thought to be largely caused by human activity. While previous mass extinctions were caused by natural phenomena such as asteroid strikes or volcanic eruptions, the Holocene extinction is thought to be caused primarily by human activity such as habitat destruction, pollution, and climate change. These activities have resulted in the loss of many plant and animal species as well as declining populations of many other species. If this trend continues, it is possible that we could lose up to 50% of all species on Earth within the next few centuries.