The term ‘The Anthropocene’ was coined in 2000 by Paul Crutzen. The word is used to describe the geological epoch that follows the Holocene, and in which humans have had an overriding influence on the earth and its atmosphere. Although still an informal reference, The Anthropocene is generally agreed to start with the industrial revolution. The word is derived from the Greek roots for anthropo- meaning “human” and -cene meaning “new.”
The predominant feature of the Anthropocene is that the earth is changing at a rate not previously experienced. For example the rate of extinction is currently greater than the rate of speciation, and is as great as previous great extinction events. The current extinction crisis has also been termed the 6th great extinction. You may be aware of the KT boundary extinction, (65 million years ago, the 5th great extinction) when the non-bird dinosaurs went extinct, and the Permian-Triassic Extinction, (251 million years ago, the 3rd great extinction) in which 96% of all marine life and 75% of terrestrial life went extinct (that was the big one).
The first wave of extinctions in this 6th mass event involve megafauna: the wooly mammoths, saber tooth tigers, cave bears and, in Australia, the marsupial lion and diprotodon. These species went extinct between 6,000 and 40,000 years ago, depending on region, and their extinctions are generally considered to be due to a combination of rapid climate change and an expanding human population coming into contact with naïve native fauna. The Blitzkrieg Hypothesis, as it has been termed (coined by Tim Flannery), explains why megafauna (elephants, rhinos, big cats) still occur in Africa, where animals evolved evasion tactics from humans while we were still honing our hunting skills. However once humans had migrated ‘out of Africa’ their hunting skills were too good for the native species that had not previously experienced human predators, and before evasion tactics could evolve in these species, the populations of large fauna were quickly hunted to extinction.
The second wave of extinctions during this 6th mass event is connected with large-scale agriculture and land clearance over the last 200-500 years, and in Australia the introduction of feral species. Small vertebrates have borne the brunt of this second wave of extinction. The highest rate of extinction is in Australia where an estimated 23 bird, 4 frog and 27 mammal species have gone extinct since 1788.
You can see how the area available to species and other landscape properties affects the extinction rate in an online extinction calculator.
Links and references
Crutzen, P. J., and E. F. Stoermer (2000). “The ‘Anthropocene'”. Global Change Newsletter 41: 17–18.
Very interesting, and also very true and relevant! I have heard many times about this and it is definitely something that we need to take into account! Although in the Mind Blowing Science article (http://mindblowingscience.com/science-by-numbers/the-5-major-mass-extinction-events/) I focused on the prehistoric extinction events, it is very important to keep in mind that the Earth does not stop changing, and mass extinctions can always happen again, as we see it happening now. Thanks for this article Andy!
Thanks Rock Scientist, I also really enjoyed your article on the prehistoric extinction events, which really helps put our current trajectory into context. My understanding is that previous mass extinctions took tens of thousands to millions of years, but the recent events are happening much more rapidly. Although speciation is a powerful process it is currently not keeping up with the rate of extinction. Has anything been done on extinction vs speciation rates during previous mass extinction events?