Estimates of current extinction rates are highly suspect, in my opinion. We are aware of something like 1.25 million species in existence now (though the estimates are all over the map) and this is orders of magnitude more than the individual species we can document for past times. Yet no one thinks (so far as I know) that we have a thousand times as many species now as, say, at the end of the Cretaceous.
No one was around to document individual species extinctions, or multiply them by modeled factors over actual observations. The work I've read on this seems bent on making things look as bad as possible, and the assumptions I've seen look unwarranted to me.
Actually, we can make intelligent estimates of species levels and species extinction rates based on such things as the normal ratios of carnivores to herbivores in an ecosystem vs. ratios of fossils of carnivores to herbivores in given periods in the past. We can also make such estimates in the present based on destruction of habitats known to be essential to various types of organisms; i.e., as such habitats are destroyed, the creatures that require them for survival must go extinct, so . . . We can also measure numbers of species found in given rock strata relative to other strata below and above them; strata particularly poor in fossils, such as are found right at the boundary between the Triassic and the Permian, signify a very high extinction rate over a geological short interval. Paleontologists, geologists, and paleobiologists don't just pull those numbers out of a hat. Their disciplines have been refining the ways they make such estimates for two hundred years, and they've got rather good at it. For an expert's observations on mass extinctions, I recommend Peter D. Ward's
No one was around to document individual species extinctions, or multiply them by modeled factors over actual observations. The work I've read on this seems bent on making things look as bad as possible, and the assumptions I've seen look unwarranted to me.
Actually, we can make intelligent estimates of species levels and species extinction rates based on such things as the normal ratios of carnivores to herbivores in an ecosystem vs. ratios of fossils of carnivores to herbivores in given periods in the past. We can also make such estimates in the present based on destruction of habitats known to be essential to various types of organisms; i.e., as such habitats are destroyed, the creatures that require them for survival must go extinct, so . . . We can also measure numbers of species found in given rock strata relative to other strata below and above them; strata particularly poor in fossils, such as are found right at the boundary between the Triassic and the Permian, signify a very high extinction rate over a geological short interval. Paleontologists, geologists, and paleobiologists don't just pull those numbers out of a hat. Their disciplines have been refining the ways they make such estimates for two hundred years, and they've got rather good at it. For an expert's observations on mass extinctions, I recommend Peter D. Ward's
Under A Green Sky: Global Warming, the Mass Extinctions of the Past, and What They Can Tell Us About Our Future and Rivers in Time: The Search for Clues to Earth's Mass Extinctions. Dr. Ward is one of the most highly regarded scientists in these areas of study, and he lays it all out very well, far better than I could. The books are available for low prices on amazon.com, or may be available in your local library.
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