Two decades ago, scientists were suggesting that the current biodiversity crisis was equivalent, or on the same path as the previous Big Five mass extinctions. Previous mass extinctions are the Ordovician-Silurian (85% species extinct), Late Devonian (75% species extinct), Permian-Triassic (96% marine species extinct, 70% terrestrial life extinct), and the Triassic-Jurassic (80% species extinct). The idea that we are in the sixth mass extinction has been discussed extensively but some parties remain somewhat unconvinced.
But two new research articles provide strong evidence that we may indeed be at the beginning of a mass extinction, driven by anthropogenic impacts.
Rull (2022) re-examines the current rates of extinction compared to the expected extinctions and the past mass extinctions. Paleontological research has given us a good idea of the average duration of a species. These averages make up the ‘background extinction rates’. When a burst in extinction occurs due to an unexpected major force (such as a meteor or anthropogenic impacts), this can exceed the background extinction rate. This occurrence is one suggestion of a mass extinction.
Based on the known extinctions listed by the International Union for Conservation of Nature (IUCN) Red List, 900 species have been documented as extinct since the year 1500. Although this mostly consists of animal species, does not include prehistoric extinctions (such as the megafaunal extinctions), and can not account for ‘dark extinctions’ (those of undiscovered/named species), this still represents 0.5% of known species on Earth with an extinction rate of 1.8 per year. This percentage does not, at face value, satisfy the criteria for a mass extinction - extinction of at least 75% species in a short period of geological time ~ 2 million years. However, if we consider that an extinction rate of 1.8 per year equals 180 per century, 75% of the total known species would be extinct in 800,000 years AND 75% of the total estimated species would be extinct in 3.6 million years.
Although this sounds like a long time away, this is within the range of a mass extinction.
Additionally, Cowie et al. (2022) have also provided strong evidence of a sixth mass extinction in their re-estimates of species extinctions. They state that previous denial of a sixth mass extinction is based on a “view of the crisis which focuses on mammals and birds and ignores invertebrates, which of course constitute the great majority of biodiversity”. Upon the inclusion of additional invertebrates, they estimate that we may have already lost between 7.5 and 13% of species on Earth. This further solidifies the claim that we may be at the beginning of the sixth mass extinction.
Okay. So this seems like pretty dark news. But we don’t have to follow this trend. Although the loss of many species is already in motion, we could save so many and even bring some back from the brink.
What do we need to do?
(1) Get vocal - tell everyone what the problem is!
(2) Get political - advocate for real, substantial action on species loss
(3) Protect and restore ecosystems - advocate for this and/or get involved in a local group
(4) Keep learning about the wonderful world we have around us and share this with others
References:
Cowie RH, Bouchet P, Fontaine B (2022) The Sixth Mass Extinction: fact, fiction or speculation? Biological Reviews
Rull V (2022) Biodiversity crisis or sixth mass extinction? Science & Society 23:e54193
EarthHow (2022) Mass Extinctions: The 5 Biggest Dying Events in History. https://earthhow.com/mass-extinctions/
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