More on ‘The Sixth Extinction’

M R Rajagopalan

The title 'The Sixth Extinction' indicates that there have been five great mass extinctions during the history of life on this planet. Extinction can be described as an event of profound loss of bio-diversity-almost total death of all life on the earth. Life on earth is supposed to be 500 million years old. The first extinction took place in the Ordovician period (Geological Era or GE for short) some 450 million years ago, when living things were mainly confined to water. The second extinction took place in the Devonian era (GE) some 350 million years ago. At this point also life was confined mainly to water. The third extinction took place during the Permian Era (GE) some 250 million years ago. This was most devastating and came close to emptying all life on earth. (This event is sometimes referred to as "the mother of all extinctions" or "the great dying"). The fourth one took place some 200 million years ago during the late Triassic or Jurassic period (GE). This great extinction is famous for the wiping out of dinosaurs and other great reptiles like the plesiosaurs, the memosaurs and the pterosaurs. Many ammonites (some kind of water snails) were also wiped out. The fifth extinction happened during the end of the Cretaceous era some 80 million years ago. Though many plants and animals were wiped out, this was not as devastating as the fourth extinction.

It has to be noted that all the five extinctions happened due to natural causes and form part of Natural History. The sixth extinction is taking place right in front of eyes of all in the present period. This is caused by the activities of the human beings and therefore, called anthropocene. Since this extinction is caused by man, it is considered 'unnatural' and hence the subtitle of the book "An unnatural history".

The author of this book [Elizabeth Kolbert] develops her theme how man has caused, or is causing the destruction in different chapters of the book.

The members of the species are not particularly swift or strong or fertile. They are, however, singularly resourceful. Gradually they push into regions with different climates, different predators, and different prey. None of the usual constraints of habitat or geography seem to check them. They cross rivers, plateaus, mountain ranges. In coastal regions, they gather shellfish; farther inland, they hunt mammals. Everywhere they settle, they adapt and innovate.

Homo sapiens, (human beings) as it has come to all itself, has reproduced at an unprecedented rate. In a single century the population doubles; then it doubles again, and then again. Vast forests are razed. Humans do this deliberately, in order to feed themselves. Less deliberately, they shift organisms from one continent to another, reassembling the biosphere.

Meanwhile, an even stranger and more radical transformation is under way. Having discovered subterranean reserves of energy, humans begin to change the composition of the atmosphere. This, in turn, alters the climate and the chemistry of the oceans. Some plants and animals adjust by moving. They climb mountains and migrate toward the poles. But a great many-at first hundreds, then thousands, and finally perhaps millions-find themselves marooned. Extinction rates soar, and the texture of life changes.

Human’s advance in new areas was always marked by destruction of animals. Thus the great mastodon (an elephant like animal but much larger) was wiped out some six thousand years ago. In fact, the American mastodon vanisned around thirteen thousand years ago. Its demise was part of a wave of disappearances that has come to be known as the megafauna (huge animals) extinction. This wave coincided with the spread of modern humans and, increasingly, is understood to have been a result of it.

The fifth chapter of the book is titled "Welcome to Anthropocene".

The word "Anthropocene" is the invention of Pul Crutzen, a Dutch chemist who shared a Nobel Prize for discovering the effects of ozone-depleting compounds. The importance of this discovery is difficult to overstate; had it not been made-and had the chemicals continued to be widely used-the ozone "hole" that opens up every spring over Antartica would have expanded until eventually it encircled the entire earth. One of Crutzen's fellow Nobelists reportedly came from his lab one night and told his wife, "The work is going well, but it looks like it might be the end of the world."

As observed by Crutzen global climate has already started departing significantly from natural behavior. In the past 15 years, the cyclones were unusually severe causing huge loss of life and property. There were also rains of huge quantity creating unprecedented floods even in deserts. This was only contrasted by severe drought which has lasted or is lasting for years in parts of Australia, California and other places. Similarly heat waves took a huge toll of life in several parts of the world.

The Anthropocene will be marked by a unique "biostratigraphical signal," a product of the current extinction even on the one hand and of the human propensity for redistributing life on the other. This signal will be permanently inscribed, they wrote, "as future evolution will take place from surviving (and frequently anthropogenically relocated) stocks".

A group of scientists led by Barbel Honisch, of Columbia's Lmaont-Doherty Earth Observatory recently reviewed the evidence for changing CO2 levels in the geologic past and concluded that although there are several severe episodes of ocecan acidifications in the record, "no past event perfectly parallels" what is happening right now in Siberia. But even this spectacular event, which created the formation known as the Siberian Traps, probably released, on an annual basis, less carbon than modern-day cars and factories and power plants.

By burning through coal and oil deposits, humans are putting carbon back into the air that has been sequestered for tens—in most cases hundreds—of millions of years. In the process, people are running geologic history not only in reverse but at warp speed.

The way corals change the world—with huge construction projects spanning multiple generations—might be likened to the way that humans do, with this crucial difference. Instead of displacing other creatures, corals support them. Thousands—perhaps millions—of species have evolved to rely on coral reefs, either directly for protection or food, or indirectly, to prey on those species that come seeking protection or food. This revolutionary venture has been under way for many geologic epochs. Researchers now believe it won't last out the Anthropocene. "It is likely that reefs will be the first major ecosystem in the modern era to become ecologically extinct" is how a trio of British scientists recently put it.

Currently about 130 million square kilometers of land on the planet are ice-free, and this is the baseline that's generally used for calculating human impacts. According to a recent study published by the Geological Society of America, people have "directly transformed" more than half of this land-roughly seventy million square kilometers-mostly by converting it to cropland and pasture, but also by building cities and shopping malls and reservoirs, and by logging and mining and quarrying.

Of the remaining sixty million square kilometers, about three-fifths is covered by forests as the authors put it, "natural but not necessarily virgin" and the rest is either high mountains or tundra or desert. According to another recent study, published by the Ecological Society of America, even such dramatic figures understate the impact. The authors of the second study, Erie Ellis of the University of Maryland and Navin Ramankutty of McGill, argue that thinking in terms of biomes defined by climate and vegetation-temperate grasslands, say, or boreal forests-no longer makes sense. Instead, they divide the world up into "anthromes". There is an "urban" anthrome that stretches over 1.3 million square kilometers, an "irrigated cropland" anthrome (2.6 million square kilometers), and a "populated forest" (11.7 million square kilometers).

This exact calculation was performed by E O Wilson. In the late nineteen-eighties; Wilson published the results in Scientific American, and on the basis of them he concluded that the contemporary extinction rate was "on the order of 10,000 times greater than the naturally occurring background rate." This, he further observed, was "reducing biological diversity to its lowest level" since the end-Cretaceous extinction, an event, he noted, that while not the worst mass extinction in history, was "by far the most famous, because it ended the age of the dinosaurs, conferred hegemony on the mammals and ultimately, for better or worse, made possible the origin of our own species."

In the eighteen hundreds, the American chestnut was the dominant deciduous tree in eastern forests in places like Connecticut, it made up close to half the standing timber. (The tree, which can resprout from the roots, did fine even when heavily logged; "not only was baby's crib likely made of chestnut," a plant pathologist named George Hepting once wrote, 'but chances were, so was the old man's coffin.') Then around the turn of the century, Cryphonectria parasitica, the fungus responsible for chestnut blight, was imported to the US, probably from Japan. Asian chestnut trees, having coevolved with Cryphonectria parasitica, were easily able to withstand the fungus, but for the American species it proved almost a hundred percent lethal. By the nineteen-fifties, it had killed off practically every chestnut in the US —some four billion trees.

Already one plant species, Poa annua, a grass from Europe, has established itself on Antarctica; since Antarctica has only two native plant species, this means that a third of its plants are now invaders.

From the standpoint of the world's biota (life forms), global travel represents a radically new phenomenon and, at the same time, a replay of the very old. The drifting apart of the continents that Wegener deduced from the fossil record is now being reversed—another way in which humans are running geologic history backward and at high speed. Think of it as a souped-up version of plate tectonics, minus the plates. By transporting Asian species to North America, and North American species to Australia, and Australian species to Africa, and European species to Antarctica, scientists are, in effect, reassembling the world into one enormous supercontinent-what biologists sometimes refer to as the New Pangaea.

‘The Sixth Extinction’ is a passionate investigation of the most terrifying extinction in the history of the world. Not only are people witnessing one of the rarest events in life's history, but also, one that is likely to be the most lasting legacy.

The author deserves compliments for writing such a book. Nonetheless, there is some problem about the book. Only persons qualified in Biology and familiar with the problems of various animals and plants becoming extinct could follow the points made by the author. General readers, not familiar with biology and problems of the extinction of speciess may find the book somewhat difficult to read and comprehend. In other words, this book is meant for some good scholars and specialists and they could really enjoy and appreciate the merits and importance of this absolutely brilliant book of Elizabeth Kolbert.

Frontier
Vol. 48, No. 10, Sep 13 - 19, 2015