Planet Earth has witnessed five mass extinctions in the past, with the last one about 65 million years wiping out the dinosaurs. Many experts have warned in the recent past that a Sixth Mass Extinction crisis is underway, and a new study has now added that Earth could have already lost about 7.5 and 13 per cent of its total species.
“Drastically increased rates of species extinctions and declining abundances of many animal and plant populations are well documented, yet some deny that these phenomena amount to mass extinction,” said Robert Cowie, lead author of the study and research professor at the UH Manoa Pacific Biosciences Research Center in the School of Ocean and Earth Science and Technology (SOEST) in a release.
“This denial is based on a highly biased assessment of the crisis which focuses on mammals and birds and ignores invertebrates, which of course constitute the great majority of biodiversity,” he added.
The team studied molluscs (land snails and slugs), the second-largest phylum in numbers of known species. According to the IUCN Red List data, molluscs have suffered a higher rate of extinction than birds and mammals. Invertebrates constitute about 95 per cent of known animal species and it is, therefore, essential to include them in the biodiversity extinction estimate, say researchers. However, among the 1.5 million described species of invertebrates, only less than 2 per cent have been fully evaluated and many remain in the ‘Data Deficient’ category.
Extrapolating the results from the molluscs, the team wrote that since 1500 about 1,50,000 to 2,60,000 of all the known species have gone extinct. But according to the IUCN, only 882 species are listed as extinct.
The paper published last week in Biological Reviews stressed that “humans are the only species able to manipulate the Earth on a grand scale, and they have allowed the current crisis to happen.”
There’ve been five extinction events in Earth’s history. Could human activity lead to a sixth? http://t.co/CZenbgfUdk pic.twitter.com/evWmUGhWm2
— Bill Gates (@BillGates) July 29, 2014
The Pulitzer Prize-winning book ‘The Sixth Extinction: An Unnatural History’ said that this is the first such event to be caused entirely by humans. “We are not just another species evolving in the face of external influences. In contrast, we are the only species that has conscious choice regarding our future and that of Earth’s biodiversity,” said Cowie.
He added that despite the rhetoric about the gravity of the crisis, political will is lacking. “Denying the crisis, accepting it without reacting, or even encouraging it constitutes an abrogation of humanity’s common responsibility and paves the way for Earth to continue on its sad trajectory towards the Sixth Mass Extinction,” said Dr. Cowie.