news details |
|
|
| Are we heading towards the sixth mass rxtinction? | | | Dr. Pragya Khanna | 1/18/2019 9:59:56 PM |
| Of the many mysterious and unexplained events that have happened on Earth over millions of years, mass extinctions are perhaps the most perplexing. Mass extinctions involve the monumental loss of plant and animal species over short time. Although, these events leave Earth ripe for evolutionary changes as new species develop to take the places of those lost, however, the phenomenon may take millions of years. About more than 90 percent of all organisms that have ever lived on Earth are extinct today. Scientists have discovered at least five different mass extinctions, referred to as the Big 5, over history when anywhere between 50% and 75% of life were lost. These different extinction events were spread across different periods on the geological time scale and had different reasons for their occurrence.
Around 439 million years ago, during Ordovician-Silurian Extinction, 86% of life on Earth was wiped out. Scientists believe two major events that resulted in this extinction were glaciation and falling sea levels. Some theories suggest that the Earth was covered in such a vast quantity of plants that they removed too much carbon dioxide from the air which drastically reduced the temperature.
Estimates propose that around 75% of species were lost around 364 million years ago during the late Devonian extinction.
The Permian-Triassic extinction, which occurred 251 million years ago, is considered the worst in all history because around 96% of species were lost. Ancient coral species were completely lost. "The Great Dying" was caused by an enormous volcanic eruption that filled the air with carbon dioxide which fed different kinds of bacteria that began emitting large amounts of methane. The Earth warmed, and the oceans became acidic. Life today descended from the 4% of surviving species.
The Triassic-Jurassic extinction happened between 199 million and 214 million years ago and as in other mass extinctions, it is believed there were several phases of species loss. The blame has been placed on an asteroid impact, climate change, and flood basalt eruptions.
Perhaps the most well-known of the Big 5, the end of the Cretaceous-Paleogene brought on the extinction of dinosaurs. A combination of volcanic activity, asteroid impact, and climate change effectively ended 76% of life on earth 65 million years ago. This extinction period allowed for the evolution of mammals on land and sharks in the sea.
A heated debate in the scientific community is whether or not earth is heading into another mass extinction. Currently, the world is in the Holocene era, plants and animals are dying off at abnormally fast rates and life as we know it is in danger. This time, however, the cause is not volcanic activity nor asteroid impacts. Human activity is triggering a change in global climate which has increased species extinction to between 10 and 100 times faster than the norm. By the year 2100, human activities such as pollution, land clearing, and overfishing may drive more than half of the world's marine and land species to extinction.
The world's species are already vanishing at an unnaturally rapid rate. And humans are altering the Earth's landscape in far-reaching ways: we've hunted animals such as the great auk to extinction; we've cleared away broad swaths of rainforest; we've transported species from their natural habitats to new continents; we've pumped billions of tons of carbon dioxide into the atmosphere and oceans, transforming the climate. A 2007 report from the Intergovernmental Panel on Climate Change suggested that 20 to 30 per cent of plant and animal species faced an increased risk of extinction this century if the planet keeps warming (though scientists are still debating these exact numbers, with some going far higher). So what happens if the extinction rate speeds up? That's one of the questions that Elizabeth Kolbert, the New Yorker science writer, explores in her excellent new book, The Sixth Extinction, an in-depth look at the science of extinction and the ways we're altering life on the planet.
Paul Ehrlich, Professor of Population Studies in Biology and a Senior Fellow at the Stanford Woods Institute for the Environment calls for fast action to conserve threatened species, populations and habitat, but warns that the window of opportunity is rapidly closing. To history's steady drumbeat, a human population growing in numbers, per capita consumption and economic inequity has altered or destroyed natural habitats. The long list of impacts includes:
l Land clearing for farming, logging and settlement
l Introduction of invasive species
l Carbon emissions that drive climate change and ocean acidification
l Toxins that alter and poison ecosystems
Now, the specter of extinction hangs over about 41 percent of all amphibian species and 26 percent of all mammals, according to the International Union for Conservation of Nature, which maintains an authoritative list of threatened and extinct species.
Nobody can say with certainty how many species there are on Earth, but the number runs well into the millions. Many of them, of course, are on the order of bacteria and spores. The other ones, the ones we can see and count and interact with, to say nothing of the ones we like, are far fewer. And, according to a new and alarming series of papers in Science, their numbers are falling fast, thanks mostly to us. Over all, there has been a human-driven decline in the populations of all species by 25% over the past 500 years, but not all groups have suffered equally. Up to a third of all species of vertebrates are now considered threatened, as are 45% of most species of invertebrates. Among the vertebrates, amphibians are getting badly hit, with 41% of species in trouble, compared to just 17% of birds, at least so far. The various orders of insects suffer differently too, 35% of Lepidopteran species are in decline (that means, 'goodbye butterflies' soon), which sounds bad enough, but it's nothing compared to the similar struggles of nearly 100% of Orthoptera species (crickets, grasshoppers and katydids, look your last).
Overexploitation, which is to say killing animals for food, clothing or the sheer perverse pleasure of it, plays a big role, especially among the so-called fascinating megafauna. So we get elephants slaughtered for their tusks, rhinos poached for their horns and tigers shot and skinned for their pelts, until oops!!! no more elephants, rhinos or tigers.
Habitat destruction is another big driver, particularly in rainforests, where 25,000 miles (75,000 km) of tree cover are lost annually, the equivalent of denuding one Panama per year, year after year. And astonishingly, you don't even have to chop or burn an ecosystem completely away to threaten its species; sometimes all it takes is cutting a few roads across it or building a few farms or homes in the wrong spots.
Then there is global warming too, which makes once-hospitable habitats too hot or dry or stormy for species adapted to different conditions.
Loss of species, the scientists point out, means loss of pollinators, which is a real problem since 75% of food crops rely on insects if they're going to thrive. Nutrient cycles, the decomposition of organic matter that feeds the soil, collapse if movable species can't get from place to place and do their living and dying in a fairly even distribution. The same is true for water quality, which relies on all manner of animals to prevent lakes and rivers and streams from becoming too algae-dense or oxygen poor. Pest control suffers as well, when animals like bats are no longer around to eat the insect pests that attack crops, it is bad news for harvests.
We may be an accident of history, but there is no question that Homo sapiens is the single most dominant species on Earth today. We arrived late on the evolutionary scene and at a time when the diversity of life on the planet was near its all-time high. And we arrived equipped with the capacity to devastate that diversity wherever human populations travelled. Blessed with reason and insight, we move toward the twenty-first century in a world of our own creation, an essentially artificial world in which (for some, at least) technology brings material comfort and leisure brings unprecedented artistic creation. So far, unfortunately, our reason and insight have not prevented us from collectively exploiting Earth's resources-biological and physical-in unprecedented ways.
Though I wrote a bit on an issue which is so complicated to solve, however, despite the gloomy outlook, there is a meaningful way forward and hope for the future, according to Ehrlich and his colleagues. "Avoiding a true sixth mass extinction will require rapid, greatly intensified efforts to conserve already threatened species, and to alleviate pressures on their populations, notably habitat loss, over-exploitation for economic gain and climate change".
We can either start to change our ways, or we can keep going the way we are, at least until the Anthropocene extinction claims one final species: Our Own. |
|
|
|
|
|
|
|
|
|
|
|
|
| |
| |
|
|
|
|
 |
|
|
|
|
STOCK UPDATE |
|
|
 |
| BSE
Sensex |
 |
| NSE
Nifty |
|
|
| |
CRICKET UPDATE |
|
|
|
|
| |
| |
|
|
| |
|
|
|
|
| |
|
|
|
|
|
|
|
|
|
|
|
|
|
