100 times greater than “normal rate”
||Ceballos G, Ehrlich PR. The misunderstood sixth mass extinction. Science. 2018 Jun 8 360(6393):1080-1081. doi: 10.1126/science.aau0191 p.1080 right column top paragraphPubMed ID29880679
|| Pimm et al., The biodiversity of species and their rates of extinction, distribution, and protection. Science. 2014 May 30 344(6187):1246752. doi: 10.1126/science.1246752  Ceballos G et al., Accelerated modern human-induced species losses: Entering the sixth mass extinction. Sci Adv. 2015 Jun 19 1(5):e1400253. doi: 10.1126/sciadv.1400253PubMed ID24876501, 26601195
||Primary source Ceballos et al.: "[Investigators] assess, using extremely conservative assumptions, whether human activities are causing a mass extinction. First, [they] use a recent estimate of a background rate of 2 mammal extinctions per 10,000 species per 100 years (that is, 2 E/MSY), which is twice as high as widely used previous estimates. [They] then compare this rate with the current rate of mammal and vertebrate extinctions."
||P.1080 right column top paragraph: "Some scientists argue that there is no reason for concern about the sixth mass extinction because extinction is normal, simply an inevitable consequence of the process of evolution (refs 3, 4). This misunderstanding ignores some critical issues. First, the rate of species extinction is now as much as 100 times that of the “normal rate” throughout geological time (primary sources)."