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Brain Booster for UPSC & State PCS Examination

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Topic: Sixth Mass Extinction

Why in News?

• According to new research published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS), the on-going sixth mass extinction may be one of the most serious environmental threats to the persistence of civilisation.

Introduction

• Researchers have described the sixth mass extinction, or the Anthropocene extinction, as the “most serious environmental problem”, since the loss of species here will be permanent.
• The research claims that this extinction is human-caused and is more immediate than climate destruction.
• Over 500 species will go extinct in 20 years because of human beings, a process that would have normally taken 10,000 years.

Mass Extinction of Species

• A mass extinction is usually defined as a loss of about three quarters of all species in existence across the entire Earth over a "short" geological period of time.
• Given the vast amount of time since life first evolved on the planet, "short" is defined as anything less than 2.8 million years.
• Since at least the Cambrian period that began around 540 million years ago when the diversity of life first exploded into a vast array of forms, only five extinction events have definitively met these mass-extinction criteria.

The Big Five

• Paleontologists recognize five big mass extinction events in the fossil record.
• At the end of the Ordovician, some 443 million years ago, an estimated 86% of all marine species disappeared.
• At the end of the Devonian, some 360 million years ago, 75% of all species went extinct.
• At the end of the Permian, some 250 million years ago, the worst extinction event so far happened, with an extinction rate of 96%.
• At the end of the Triassic, some 201 million years ago, 80% of all species disappeared from the fossil record.
• The most famous mass extinction happened at the end of the Cretaceous, some 65 million years ago, when 76% of all species went extinct, including the dinosaurs.
• These extinctions were caused by “catastrophic alterations” to the environment, such as massive volcanic eruptions, depletion of oceanic oxygen or collision with an asteroid.
• After each of these extinctions, it took millions of years to regain species comparable to those that existed before the event.

Sixth or Not?

• The Earth is currently experiencing an extinction crisis largely due to the exploitation of the planet by people. But whether this constitutes a sixth mass extinction depends on whether today's extinction rate is greater than the "normal" or "background" rate that occurs between mass extinctions.
• This background rate indicates how fast species would be expected to disappear in absence of human endeavour, and it's mostly measured using the fossil record to count how many species died out between mass extinction events.
• In contrast to the the Big Five, today's species losses are driven by a mix of direct and indirect human activities, such as the destruction and fragmentation of habitats, direct exploitation like fishing and hunting, chemical pollution, invasive species, and human-caused global warming.
• Even considering a conservative background rate of two extinctions per million species-years, the number of species that have gone extinct in the last century would have otherwise taken between 800 and 10,000 years to disappear if they were merely succumbing to the expected extinctions that happen at random. This alone supports the notion that the Earth is at least experiencing many more extinctions than expected from the background rate.