Extinction has been a natural part of our planet's evolutionary history. Over the last 3.5 billion years, 99% of the four billion species are gone extinct. There have been five major extinction events called "The Big Five" happened in the history of the earth, named Permian, Devonian, Ordovician, Triassic, and Cretaceous that exhibited a loss of over 75% of estimated species in the past 540 million years. As per recent studies, the estimated current rate of extinction is higher than the background rate suggesting the sixth mass extinction. But how did we get to this conclusion? There are a few metrics we use to answer this question. Extinction per million species-years (E/MSY) is used to estimate the background rate from the fossil extinction that took place in millions of years or more. To categorize the current extinction episode on the scale, it requires both the current extinction rate and how far it is from the background rate, and also calculate the number of years needed for 75% of species to go extinct based on the current rates. Based on data gathered over the previous 500 years, the present extinction rate for mammals, amphibians, birds, and reptiles is greater than the rate of the Big Five extinctions in geological time. Extinction magnitude of previous mass extinctions suggests unusual climate dynamics, atmospheric composition, and abnormally high-intensity ecological stressors including some random accidents like a Cretaceous asteroid impact. Since humans are the primary drivers of the environment, it's important to look after extreme conditions to prevent the intensification of the sixth mass extinction.

There are some specific questions that we need to focus on to understand the mass extinction in more detail.

Question- 1. What are the data comparison problems and challenges when comparing the Big FIVE mass extinctions and the anthropogenic mass extinctions?

Ans. The major data comparison problem which arrives when we compare the ‘BIG Five’ mass extinction with the anthropogenic mass extinction is due to –

a) Geography – Since the distribution of fossils is very uneven and scattered over the globe some species which could have been used in determining the extinction rate of the big five may be left out due to their inaccessibility. Modern-day database of the distribution of species is very well-defined so anthropogenic mass extinction can be defined very well.

b) Taxa available for study – Mostly species which have preservable hard parts that fossilized very well are used to study mass extinction and depending upon the type of taxa we choose our extinction event and rate may change.

c) Taxonomy – Due to the lack of a precise database, to define the Big five mass extinction fossils are analysed at a genus level rather than the species level. Whereas modern-day taxa are defined at a species level.

d) Assessing extinction – Modern-day extinction is recorded when an individual of a particular species is no longer sighted. In the fossil record, extinction is defined as when a taxon is permanently extinct from the fossil record.

e) Time – In modern times we have large no of species over a very short time, however, in the fossil record, we have very limited samples of species that are discontinuously distributed throughout the time interval.

Question-2 What is E/MSY? How similar/different is this metric from the extinction rates?

Ans. E/MSY shows extinctions per million species-years, which is a metric to quantify the extinction rate. As we have known other metrics like per capita extinctions and normalised per capita extinctions to quantify the extinction rate. E/MSY means the extinction of species per million species per year which is quite similar to the normalised per capita extinctions.

Question-3 What are your thoughts on the possibility of an ongoing mass-extinction?

Ans. As the current rate of extinction is relatively faster than the big five extinctions which would put us on the course for a sixth mass extinction if continued this way. But there are many species which are understudied, or some might have gone extinct before we had a chance to identify them which might show up later as a fossil record in future. So there are chances of variation in the estimated magnitude rate for 6th mass extinction. And talking about critically endangered or endangered species could also go extinct early which would elevate the extinction rate massively. But since we are the primary drivers of the environment, we can prevent the sixth mass extinction.

The only comprehensive environmental management strategy that will preserve and confide the majority of the negative environmental effects of anthropogenic activities simultaneously enhances the restoration of the sixth mass extinction. The sixth mass extinction has not occurred yet, but the rate at which the vast range of population is declining or has already declined, the biodiversity is suffering. Biodiversity is changing at a greater rate because of the presence of anthropogenic activities. This is the fact that there is an interconnected array of threats to species and ecosystems. According to the research, many marine species, basically the marine realm, are facing a significant threat. Some species have gone to extinction, but we are unsure whether they are part of sixth mass extinction. Anthropogenic climate change has a detrimental effect on biodiversity and can not go undetected. The threat of technological advancement also exists, as it could impact the connection between the species and biodiversity. The present concern could also be massive carbon emissions leading to rapid global warming. Will this lead to a mass extinction? As Earth has already experienced a similar influx of atmospheric carbon and entered a "hothouse" state around 56 million years ago. So, it could be possible for us to experience a climate catastrophe. But again, this should not limit our understanding of the sixth mass extinction. Dedicated conservation agencies are trying hard, focusing mainly on the mammals and birds that are on the verge of extinction, among which some species could have been saved. The complete scope and distribution of threats need to be better understood and taken into account in conservation planning and decision-making in order to prevent the sixth mass extinction. Although it may not be possible for many biologists or palaeontologists to suggest whether we are in or approaching the sixth mass extinction. To understand it better, we need to dig deep past the Earth more broadly for guidance in the hope of shaping Earth's future.

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