MASS EXTINCTIONS: FIVE OVER THE COURSE OF 540 MILLION YEARS.

Destaque para a coluna semanal WHAT’S NEW do físico Robert L. Park:

1. The extinction of species is to be expected in a violent universe; that's why we have paleontologists. They have identified five mass extinctions over the past 540 million years in which the number of species declined by over 75% in a geologically brief interval. These mass extinctions mark the end of the Ordovician, Devonian, Permian, Triassic and Cretaceous Periods. Recovery from each of these episodes took millions of years. There is a growing conviction among paleobiologists that Earth is on the brink of mass extinction-six. The only exception is Homo sapiens. By any measure, Homo sapiens is thriving at the expense of wild species. Now numbering almost seven billion, the population has doubled since Paul Ehrlich published the Population Bomb (Oxford, 1968) which warned of mass starvation by the turn-of-the-century. Ironically, the developed nations are today confronted with an obesity epidemic.

2. A review article in yesterday's Nature by Barnosky et al. at UC Berkeley asks, "Has the Earth's sixth mass extinction already arrived?” The article answers in the affirmative. The current extinction crisis, number six, unlike previous episodes, results from the actions of a single species, Homo sapiens. The evidence is everywhere, global warming, enormous ocean garbage patches, destruction of the great ocean fisheries, deforestation, etc. Of the 5,487 known species in the class Mammalia, for example, 1,141 are considered by the International Union for Conservation of Nature (IUCN) to be "threatened with extinction." The ancient concept of a "Balance of Nature," described by Herodotus in 425BC, is still frequently invoked to explain apparent homeostasis between species. But there is no homeostasis; it was simply an illusion created by the short lifespan of humans. That's why we have paleontologists. The balance-of-nature gave way to Darwin's "origin of species by natural selection" in 1858. There are still frequent references to the Balance of Nature by those who don't understand evolution. More recently, the Gaia hypothesis has developed a following. It’s a more spiritual version of homeostasis in which Earth is viewed as a single organism. That seems to imply a plan, which would put Gaia in the category of superstition.

Robert Park