Environment and science

Are we facing a sixth Mass Extinction? Can we do anything about it?

An essay exploring the topic of mass extinction and whether or not we are indeed experiencing the beginning of a sixth one.

Forest fire in the Boise National Forest, Idaho. Image credit: David R. Frazier, National Geographic.

Introduction

Over the course of the earth’s history, as we know it, there have been a total of five Mass Extinction events. It is now the general agreement, although there are people who counter the argument (Thomas, 2017), that we are currently experiencing a Sixth Mass Extinction. Previously, all the other five Mass Extinctions have been caused by global natural phenomena (Bond and Grasby, 2017). This time, however, the Mass Extinction is all to blame on us humans (Alroy, 2008). Many of today’s extinctions can be directly correlated to anthropogenic activity and are completely unrelated to the known causes of previous Mass Extinctions (Alroy, 2008).

Some people claim that the current rate of loss of species is not sufficient enough to claim a Mass Extinction (Cowie et al., 2022), despite the considerable evidence of a global biodiversity crisis and the massive reduction in habitats and species abundance. To support this claim you could use the statistics from the IUCN Red List, which suggest that the rate of species loss does not differ greatly from the background rate. However, the IUCN Red List has been criticized for being heavily biased toward birds and mammals (Cowie et al., 2022). There have only been a tiny fraction of invertebrates properly evaluated against the conservation criteria. Another issue with using the IUCN listings as the sole source of evidence for inferring a Mass Extinction or not is that it only accounts for 5.6% of the total of ~2.14 million described animal and plant species accepted by IUCN (2020), 120,372 species in total.

If the estimates of the true number of invertebrate extinction were to be incorporated into the IUCN Red List we would see the current extinction rate greatly surpass the background rate (Cowie et al., 2022), indicating that we may well be witnessing the beginning of the Sixth Mass Extinction. One example of invertebrates experiencing species losses is molluscs, the second largest phylum in the number of known species. Since around 1500AD, as many as 13% (260,000) of all known mollusc species have gone extinct (Gibbons, 2007).

Being the only species capable of manipulating the Earth on such an immense scale, we as humans have allowed this current crisis to occur. There have been, and continue to be, attempts at conservation at various levels, however, the amount of resources and cooperation needed to protect all living species far exceeds the current resources put toward such efforts.

So what exactly is a Mass Extinction?

A Mass Extinction is when a high percentage of biodiversity, or specific species (mammals, plants, fish, birds, fungi, reptiles, etc.), dies out within a short period of geological time. A ‘short period’ of geological time could refer to a span of thousands or possibly millions of years. The last Mass Extinction, the Cretaceous-Paleogene extinction, occurred 66.5 million years ago.

Splendid Poison Arrow Frog (Dendrobatidae). The species of frog was classified as extinct in 2020 by IUCN reports. Jerry Kirkhart.

More than 99% of all life that has ever existed on Earth is extinct (Greshko, 2019). New species are constantly evolving and adapting to their environment, in a global-scale fight for survival, and as a result, older species eventually die out. However, the rate of extinction has not been constant. As previously discussed, there is a general consensus on the fact that there have been five Mass Extinction events, where 75% — 90% of all species on Earth disappeared (Begum, 2021).

Although Mass Extinctions are fatal and catastrophic events of global proportion, they also give the opportunity for new forms of life to emerge. The Cretaceous-Paleogene extinction, for example, killed off the terrestrial dinosaurs and allowed mammals and birds to flourish, diversify and evolve.

What are the previous five Mass Extinctions?

Five Mass Extinctions have changed life on Earth dramatically. There is evidence to suggest causes for some of them, but others still remain a mystery.

1. The Ordovician-Silurian mass extinction happened 443 million years ago and killed off an estimated 85% of all species. It is thought that plummeting temperatures and dramatic drops in sea levels are what caused it. A period of rapid warming followed, and many small marine creatures died out.
2. The Devonian mass extinction occurred 374 million years ago and killed off almost three-quarters of all species, the majority of which were marine invertebrates that lived at the bottom of the oceans. We do not know the exact reason for the mass extinction event. We do know, however, that this was a period of several environmental changes, such as the rising and falling of sea levels, reduction in carbon dioxide and oxygen in the atmosphere, and global warming and cooling.
3. The Permian mass extinction took place 250 million years ago. This is the largest and most devastating of the five. Around 95% of all species were eradicated, including the majority of vertebrates which had started to evolve by then. It is also known as the Great Dying. Some theories suggest that Earth may have been hit by a massive asteroid, which filled the atmosphere with dust that blocked the light from the Sun and resulted in acid rain. Another theory is that there was a large volcanic eruption that dramatically increased carbon dioxide levels in the atmosphere and made the seas toxic.
4. The Triassic mass extinction happened 200 million years ago, causing the death of approximately 80% of Earth’s species, including many dinosaur species. Scientists believe the event was probably caused by tremendous geological activity, which increased global temperatures and carbon dioxide levels, and ocean acidification.
5. The Cretaceous mass extinction occurred 66 million years ago. About 78% of all species were wiped out, including the last non-avian dinosaurs. Scientists believe that this was most likely caused by an asteroid smashing into the planet.

What are the causes of a potential sixth Mass Extinction?

It is widely agreed upon that the events which caused the previous five Mass Extinction events were caused by devastating natural phenomena. The sixth, however, is driven almost entirely by human activity (Greshko, 2019). The primary anthropogenic activities contributing to the rapid decline in species across the globe include (though are not limited to) habitat destruction, unsustainable energy and land use, and global warming. A report by Living Planet claims that 30% of all land that sustains biodiversity is being used for the production of food.

An aerial photo depicting a typical agricultural area near Ottawa, Ontario, Canada (OMNR, 2010). To meet the growing demand for human food, forested land (shown in dark green) has been replaced by agricultural crops (Image credit: Carleton University under licence from Ontario Ministry of Natural Resources.)

Agriculture is responsible for 80% of deforestation across the globe and uses 70% of the planet’s total freshwater supply (Greshko, 2019), resulting in the complete devastation of these habitats and the species that inhabit them. As such, it is clear to see that how and where our food is produced has one of the largest impacts on human-related threats to the environment and species extinction. The unsustainable manner of our food consumption and production contributes massively to greenhouse gas emissions and as a result, raises global atmospheric temperatures (Ritchie and Roser, 2020). Consequentially, we shall start to experience more havoc and un-before-seen natural phenomena (IPCC, 2021). The results of a climate crisis include (but are not limited to) severe droughts, an increase in flooding, and more intense storms. The changing climate will only make the challenges linked to food production even harder, creating inhospitable habitats and increasing the rate of species extinction. An increased frequency of floods and droughts, in regions across the globe, has made maintaining crops and producing sufficient amounts of food increasingly difficult. Biodiversity loss, climate change, and our food system are all intertwined and are constantly applying more and more pressure on the planet.

Anthropomorphic activity

Since the start of the Industrial Revolution (1830/the 40s), we have experienced massive increases in carbon dioxide levels in the atmosphere at a rapid rate. There are studies which show we have contributed 365 billion tons of carbon dioxide by burning fossil fuels and an additional 180 billion through deforestation. Annually, we are adding an extra 9 billion tons of carbon dioxide into the atmosphere. That number is increasing by 6% annually. To put it into perspective, we have been the sole reason for the planet’s highest levels of concentration of carbon dioxide in the last several million years.

Coral reefs are a fundamental habitat for thousands of marine species, providing them with food and protection. As such, many species have co-evolved with corals. Ocean acidification, a result of human activity, may cause corals to become extinct within the next century (Fabricus, et al., 2011). Before the industrial revolution, the aragonite saturation state of underwater reefs was between 4 an 5. However, if our current carbon emission rate is sustained and increased, by 2060, a region above 3.5 will not exist (Fabricus, et al., 2011). This will require further use of energy, in our attempts to conserve coral reefs. One minor change can cause a domino effect in various ecological systems.

Dead coral in the Great Barrier Reef. (Image credit: Andreas Dietzel, BBC)

Global warming is often seen as more of a threat to cold-loving species, as opposed to warm-loving species (Barnosky and Anthony, 2009). Polar ice caps are melting, and increasingly so with the increasing rise in temperatures. Species dependent on the ice are faced with extreme challenges that may ultimately force them to extinction. All life is interconnected, and over time, the fragmentation of habitats leads to a decreased amount of biodiversity within fragmented areas (Wright and Emma, 2010). This occurs, in part, as a result of the fragmented habitat areas not being able to support a large or stable number of species members (Wright and Emma, 2010). The smaller the species’ population, the more vulnerable it is to variables within its environment. The fragmentation of habitat areas also makes it more difficult for species to reach and repopulate them.

In Southeast Asia, the Sumatran Rhino once had such a high population that it was considered an agricultural pest (Greshko, 2019). However, as a result of the rhino’s habitat being destroyed through deforestation, its habitat became greatly fragmented. Currently, the rhino population stands at less than a hundred (Gokkon, 2022). A captive breeding program in the 1980s resulted in the deaths of several rhinos and was widely seen as a failure (Greshko, 2019). Recently, however, new technology has emerged, which may allow scientists to produce new living cells from a dead Sumatran Rhino in an effort to prevent the extinction of this critically endangered species (Zywitza, et al. 2022).

Kertam, a young male Sumatran rhinoceros from Borneo whose genome was sequenced for stem cell study. Image by Scubazoo.

Survival of the fittest

Such is the nature of our planet, that all life is in a constant evolutionary arms race. An arms race where each species is required to protect itself from potential predators, while simultaneously being stronger and fitter than the competition within their own groups. When a new environmental variable is suddenly introduced, for example, a new fungus, bacterium, or virus, species have no defences against it (Ricciardi and Anthony, 2007). Situations such as this can be fatal to entire species, as was the case of the estimated 5 million North American bats killed by the psychophrilic fungus Geomyces destructan, also known as ‘bat white-nose syndrome’.

Bat with white-nose syndrome (Image credit: von Linded, National Park Service.)

For about 100,000 years, Europe was home to the Neanderthals. Then, about 30,000 years ago, the Neanderthals vanished. According to fossil records, modern humans started showing up in Europe about 40,000 years ago (Callaway and Ewen, 2014). It is claimed, that within 10,000 years, the Neanderthals were bred out (Alroy and John, 1999). By means of molecula sequencing, studies have shown that there is 1–4% Neanderthal DNA in all non-African humans (Fu, et al. 2015). This infers that Neanderthals and humans interbred, until eventually Neanderthals were bred out entirely.

What does Mass Extinction mean for us humans?

As mentioned previously, species do not live in isolation; we are all interconnected. Species interact with other species in ways that are beneficial to us as humans. Such benefits include clean water, clean air, and healthy soils. All species serve some function within their greater environment. When one of these species has reached the point that it cannot carry out its function due to a huge decrease in population, other species are impacted, essentially disrupting the way the ecosystem operates and provides its benefits. As a result, the potential for species extinction rises (Greshko, 2019). Keeping a close eye on these trends is of utmost importance in order to measure the overall health of the ecosystem. Considerable drops in populations of species are a telling sign that the ecosystem is breaking down, indicating a potential larger system failure.

Currently, the rate of species extinction is approximately 1,000–10,000 times higher than the background extinction rate (Cowie et al., 2022). Although extinctions are an expected part of the evolutionary process, the current rates of species extinction and species population decline are enough to cause detrimental effects on ecological functions supporting human life on the planet. Such functions include a stable climate, productive farmland and fisheries, and predictable rainfalls.

If action is not taken to combat the decline of species population, the losses we face will take decades, at best, to recover from. This will also make life on the planet harder to support, both for current and future generations.

What can we do?

While the sixth Mass Extinction event may not yet have taken place, the heightened rates of population declines and species extinctions have already taken place and are continuing. Biodiversity is clearly being affected at a much greater rate than it would otherwise, in the absence of human activity. It seems likely, then, we are experiencing a sixth. Undoubtedly, as a result of human activity.

As humans, we are the only species capable of manipulating the natural environment at such a grand scale and as such we are the only species with the power and choice to reverse some of the damages we have caused (Deer, 2019). We are not just another species living its life, without the complex conscientious foresite to make decisions and act upon them. We differ from asteroids, the cause of previous mass extincitons, in the sense we have choice. As such, we also have the responsibility and obligation to be the caretakers for the rest of the planet, ideally in a non-humancentric approach.

While many conservation efforts seem to have made little difference to the destructive course our planet is on, there is still evidence to show that some conservation efforts are effective (Cowie et al., 2022). There have been successful efforts to impose hunting bans on marine mammals, seeing a resurgence in specific populations (Bejder, et all., 2016). There has been a recovery of native faunas after the removal of invasive species on islands (Jones et al., 2016). However, these efforts are not enough on their own.

Changes need to be made to the manner in which we use and access natural resources. Other changes need to be made at a governmental and corporate level. Individually we can do our best to be responsible for our actions, however, we may be more effective by putting more effort into pressurising policymakers and businesses to reduce emissions.

Conclusion

Often, beauty is derived from interpretations and perspectives we have of nature. Biodiversity and its varieties are what makes life so fascinating. Furthermore, this beauty also has a functional role in the interconnected operations of the planet. We are facing a massive biodiversity crisis and are witnessing species loss rates that point to the fact that we are indeed facing the sixth Mass Extinction. Accepting this or doing nothing about it will only speed up our demise and the majority of all other life on Earth. There will always be hope as long as people are working to change the current systems we are using so ignorantly.

References

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