We’re all going to die: The 6th mass extinction

By Zhuying Ser

Although the title of this article is dramatic and possibly over exaggerated, it is not entirely untrue. If the “we” in the statement represents the entirety of life on Earth, statistics show that we are in fact dying. The biodiversity of living organisms in the world is rapidly dropping as more and more organisms are threatened with extinction. Extinction is not uncommon and certainly not unnatural, but it is usually balanced out by speciation. This dual interaction between extinction and speciation played key roles in evolution to bring about the living organisms we have today. However, scientists all around the world including Sir David Attenborough have called upon world leaders to warn them of alarming rates of extinction and the consequences that will follow.

In the 3.5-billion-year history of the Earth, it is estimated that about 4 billion distinct species have evolved. Despite this, only 1% of that total biodiversity remains. Natural extinction resulting from interspecific competition and the past mass extinctions are partly responsible for this but we as a human race are still to blame. In 2019, it was estimated that about 1 million species were threatened with extinction  (Barnosky, Matzke & Tomiya, 2011).

Palaeontologists define mass extinctions as a 75% loss of the Earth’s biodiversity. Reduction in biodiversity on this scale has only happened 5 times in the past 540 million years. Extinctions are occurring constantly during the Earth’s timeline but at varying densities. So, whether the extinction crisis of our time will be defined as the 6th mass extinction will be relative to the 5 previous extreme events of biodiversity loss. The first mass extinction, named the Ordovician event, arose about 445 million-years-ago (MYA) due to an onset of alternating glacial and interglacial episodes, removing 86% of the biodiversity from that time (Sheehan, 2001). The Devonian event occurred 359 MYA, causing the extinction of 75% of the species due to global cooling and warming. The third mass extinction, the Permian event, reduced biodiversity by 96% as a result of Siberian volcanic activity about 251 MYA (Berner, 2002). The Triassic event, which occurred about 200 years ago, reduced the biodiversity to 20% of its original capacity when magmatic activity below the Earth’s Surface caused global warming and calcification in the oceans. The most recent mass extinction event was the Cretaceous event, which happened 25 MYA, when an extremely bright meteor, a bolide, struck our planet. The bolide collision induced global warming, anoxia and eutrophication episodes which all contributed to the extinction of 76% of the species (Petersen, Dutton & Lohmann, 2016).

In order to asses if we are on our way to a 6th extinction we need to compare the modern rates of extinction to the previous records of extinction: fossils. The evidence for the past mass extinctions are clear; all over the world, remnants of many unfamiliar life forms are found in one layer of rocks and then a significantly less on the next. However, problems arise when we evaluate the validity of fossil records. Only specific organisms usually with particular types of exoskeletons or membranes are able to be preserved in sediment. This produces an unrepresentative picture of the biodiversity at that time. Although, modern data on the extinction threats of extant species today are not particularly accurate either. The international Union for Conservation of Nature (IUCN) have said that they have only conducted formal analyses of extinction on less than 3% of species (Barnosky, Matzke & Tomiya, 2011).

Although researchers at Nature have found that the current extinction crisis is not yet classified as a mass extinction, this does not mean that the situation is not serious. The severity of the current crisis is expressed as dire due to how dramatic the changes that will have to occur to prevent the current threats to biodiversity driving the existing species to extinction will be. These threats are fragmented habitats; co-opting resources; introduction of non-native species and the changing global climate, all of these being the result of human activity.

Many people in the past have recognised the damage we are doing to our planet and have been convincing heads of states and governments of the pressing issue. Even when countries around the world come together to set out plans to change our negative impact on the planet, it is easier said than done. For example, in 2010 when the multilateral treaty, the Convention on Biological Diversity (CBD) came together to put together a plan for change they produced the Aichi Biodiversity targets. These were 20 planned out steps that aimed to alleviate pressure on endangered species by 2020. However, in 2019 it was reported that none of the 20 targets were fully met (Briggs, 2020).

Recently, when Sir David Attenborough released a film to raise awareness of our biodiversity problem, many of the public became more aware of the severity of the crisis. This can definitely be seen as a step in the right direction and we can only hope that our words and promises spur action to effectively save our planet.

References:

Barnosky, A., Matzke, N. & Tomiya, S. (2011) Has the Earth’s sixth mass extinction already arrived? Nature. 

Berner, R. A. (2002) Examination of hypotheses for the Permo-Triassic boundary extinction by carbon cycle modeling. Proceedings of the National Academy of Sciences – PNAS. 99 (7), 4172-4177. Available from: doi: 10.1073/pnas.032095199. 

Briggs, H. (Sep 2020) Sir David Attenborough warns world leaders over extinction crisis. BBC. 

Petersen, S. V., Dutton, A. & Lohmann, K. C. (2016) End-Cretaceous extinction in Antarctica linked to both Deccan volcanism and meteorite impact via climate change. Nature Communications. 7 (1), 12079. Available from: doi: 10.1038/ncomms12079. 

Sheehan, P. M. (2001) The Late Ordovician Mass Extinction. Annual Review of Earth and Planetary Sciences. 29 (1), 331-364. Available from: https://doi.org/10.1146/annurev.earth.29.1.331. Available from: doi: 10.1146/annurev.earth.29.1.331. 

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