When teen environment activist Greta Thunberg warned the world that “We are at the beginning of a 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 can clearly see that the weather around us has changed in the last decade or so. The human life span is quite insignificant when we consider the age of the earth and the time since life has existed on the planet.
Dinosaurs became extinct from earth about 66 million years ago. They roamed the planet for at least 230 million years. That is a long time, much longer than the time humans have existed on earth. It was an era when the shape of the continents was different. All the landmass was together and there were no continents.
After reigning the earth for 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 from 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 rapid changes in temperature pose a big risk to life forms on the planet. In any given era, the lives on the planet would have evolved to be able to survive in particular climatic conditions. And when these conditions change, 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 severe ice age that lowered sea levels. The planet’s temperature fell drastically chilling the planet. This is said to happen because the level of carbon dioxide, which has the property to trap heat, fell. 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 drastically 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
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 species ceased to exist. This happened because of the rise in earth’s temperature. An enormous volcanic eruption increased the level of carbon dioxide in the atmosphere. Carbon dioxide is a greenhouse gas, which means 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). The led to a surge in global temperatures, oceans became acidic and poisonous hydrogen sulfide levels increased. All these combined made earth inhabitable and 96 per cent of species became 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 monsoons. Weather changes became erratic and a global warning like phenomenon brought about changes in climate. One theory also speculates that an asteroid collision may have had an adverse effect on climatic conditions.
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 and 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.
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 note that in our lifetime itself, we can notice changes in the climate. Some say that the changes in climate which have happened in the last 100 years, would otherwise have taken much longer time. If the change is spread over a long time, then the species get 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.