New Delhi, Oct 09: When teen environment activist Greta Thunberg warned the world that "We are at the beginning of mass extinction", many may have thought that she couldn't be serious. Yes, the planet is becoming hotter, Yes, there is pollution and deforestation, but is the situation really so grave that it poses threat to our very existence?
Well, the answer is 'YES' and the process may already have begun. The unpredictable and erratic natural calamities are on a rise. And if we carefully give a thought, we would clearly be able to see that the climate around us has changed in the few decades or so. The human life span is quite insignificant considering the age of the earth and the time when life first appeared on the planet.
Dinosaurs became extinct from earth about 66 million years ago. They roamed the planet for around 230 million years. That is a long time, much much longer than the time humans have existed on earth. It was an era when the earth was very different from what it is now. Almost all of the earth's landmass was divided into two large super-continents - one in the north (referred to as Laurasia) and the other in the south (known as Gondwana). This was around 80 to 140 million years ago on the geological time scale. Before that, around 200 million years ago, all the landmass on earth was concentrated into a single supercontinent which existed near the equator. All the landmass was together and there were no separate continents as it is now.
After reigning the earth for around 230 million years, something happened which changed the climate of the planet some 66 million years ago, and around 75 per cent of the species were wiped out of the planet. Whenever there has been a sharp change in the average temperature of the earth, the planet has witnessed mass extinction. The extinction that wiped out dinosaur is called the Cretaceous-Paleogene extinction event and it was the fifth mass extinction since life evolved on earth.
There are various theories to explain the Cretaceous-Paleogene extinction and all of them try to explain what resulted in sudden climate change. Theories may be different, but the established fact is that sudden changes in the earth's temperature pose a big risk to the life forms on the planet. In any given era, the life forms on the planet would have evolved to be able to survive in particular climatic conditions. And when these conditions change very fast, species do not get time to acclimatise and go extinct.
Five major MASS EXTINCTIONS in earth's history:
End Ordovician - 444 million years ago:
86 per cent of the species that existed then went extinct. The main reason was the beginning of the severe ice age that lowered the earth's temperature as well as sea levels. The planet's temperature fell drastically, and the planet became very cold. This is said to have happened because of the sharp fall in the level of carbon dioxide, which has the property to trap heat from the sunlight. Scientists are of opinion that the earth was covered in such a vast quantity of plants that they removed too much carbon dioxide from the air which significantly reduced the temperature.
Late Devonian - 375 million years ago:
75 per cent of the species that existed then went extinct. The reasons are many, but broadly it can be said that the extinction happened because of the drop in oxygen level on earth. The surface of the earth was enveloped by giant plants and their deep roots released nutrients into the oceans. The nutrient-rich oceans supported the growth of algae-like life forms. This algal bloom sucked the oxygen out of the water and ocean animals started to become extinct. The theory also says that active volcanos emitted too much ash and volcanic debris into the atmosphere which blocked the sunlight, and the temperature fell drastically.
End Permian - 251 million years ago (also called Permian-Triassic extinction)
96 per cent of the species that existed then went extinct. The Permian-Triassic extinction almost ended life on earth as 96 per cent of the species ceased to exist. This happened because of the rise in earth's temperature. An enormous volcanic eruption is believed to have increased the level of carbon dioxide in the atmosphere. Carbon dioxide is a greenhouse gas, which means that it has the property to absorb heat from sunlight and emit it later. Increase in carbon dioxide raised the temperature of the earth. To add to this, the bacteria that dwelled on carbon dioxide flourished and began emitting large amounts of methane (another greenhouse gas). This led to a steep surge in global temperatures, oceans became acidic and poisonous hydrogen sulfide levels increased. All these combined made earth inhabitable and 96 per cent of the species went extinct.
Triassic-Jurassic extinction - 200 million years ago:
80 per cent of the species that existed then went extinct. This remains the most mysterious of the mass extinctions and scientists have not been able to give a sound reason for this. It is believed that something happened because of which large amounts of carbon dioxide was released. This led to climate change, resulting in long droughts interrupted by severe rains. Weather changes became erratic and global warming like phenomenon brought about changes in the climate. One theory also speculates that an asteroid collision may have had an adverse effect on climatic conditions. If a large celestial body collides with earth then it is likely to raise so much dust and debris that sunlight would be blocked for years, and there would be a sharp fall in temperature.
Cretaceous-Paleogene extinction - 66 million years ago:
76 per cent of the species that existed then went extinct. The dinosaurs were wiped out from the planet because of drastic change in climate and temperatures. Volcanic activity, asteroid impact, and climate change are said to be the reasons for this sudden change in climate. Some say that earth's green cover began shrinking and this led to an increase in greenhouse gases.
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Conclusion: Are we on the brink of EXTINCTION?
It may be noted that greenhouse gases, especially the carbon dioxide levels had a major role in almost all the past five mass extinctions. Human activity is changing the planet more rapidly than ever. We can easily notice that in our lifetime itself, plenty of changes take place in the climate. Some say that the changes in climate which have happened in the last 100 years, would otherwise have taken much much longer time. If the change is spread over a long period of time, then the species get a chance to evolve and acclimatise. Human activity is triggering a change in global climate. The vehicular emissions, burning of fossil fuels, cutting of trees and thinning of the ozone layer have collectively increased the average temperature of the earth. Some experts opine that the process of sixth extinction may already have begun.
Human greed to consume resources of the planet and damage nature is only speeding up the sixth extinction. Factories and emissions have increased the emission of greenhouse gases, which would trap heat from the sunlight and increase the average global temperature. Life forms are linked by a sophisticated process called the food chain, and human activities can disrupt food chain which would make the availability of food scarce for some species. Carbon Dioxide rise may lead to melting of the polar ice which would raise sea levels across the planet. We can see from the past that change in sea level and increase in carbon dioxide have led to mass extinctions. Given all this, it would not be wrong to say that we are on the brink of sixth MASS EXTINCTION.