Extinction

Species die. Sometimes, a majority of the species instantly die in a wave of mass extinction. This has happened five times in the past. Around 450 million years ago, 60-70% of the marine population died due to ice age. Less than another 100 million years later, climate changed and wiped out a similar number. Another 110 million years later, massive volcanic eruptions in Siberia, which caused huge global warming, killed 95% of the species. Around 200 million years ago, “another outburst of volcanism” killed 75%, and “left the Earth clear for dinosaurs to flourish.” Sixty five million years ago, a giant asteroid fell in Mexico, and wiped out the dinosaurs.

A recent study concludes that our planet is in the midst of a sixth mass extinction, which is entirely manmade. The researchers, led by Gerardo Ceballos, describe the phenomenon as a “biological annihilation”. Using a sample of 27,600 vertebrates, and detailed analysis of 177 mammals, the study finds that the “rate of population loss… is extremely high — even in ‘species of low concerns.’ In our sample, comprising nearly half of known vertebrates, 32% are decreasing, that is, they have decreased in population size and range. In the 177 mammals… all have lost 30% or more of their geographic range and more than 40%... have experienced severe population declines with over 80% range shrinkage. In effect, the area over which these animals are found has considerably reduced, and their populations in remaining areas have radically shrunk.”

The situation in the cases of land and marine invertebrates is worse. “For example, it is estimated that 42% of 3,623 terrestrial invertebrate species, and 25% of 1,306 species of marine invertebrates… are classified as threatened with extinction.” But scientists’ obsession with extinction, rather than geographical and population losses, generates a feeling that the biodiversity loss is not a matter of “deep concern” and can be addressed. This is not true for two reasons: the disappearance of populations always precedes extinction, and rapid decrease in the number of individuals within populations expedite the trend.

Yet another concern needs to be highlighted here. Over the last century, 200 vertebrates have disappeared, a rate of two per year. This does not seem much. But, as the paper explains, if the rate is measured on the basis of natural historical data, or ‘normal extinction’ rate, such losses had to occur over up to 10,000 years and not 100 years. “In the last few decades, habitat loss, over-exploitation, invasive organisms, pollution, toxification, climate disruption, as well as interactions among these factors, have led to catastrophic declines….”