Words by: Natasha Bloomfield
Mass extinctions occur when there is a widespread and rapid decrease of animal species on Earth at a rate that significantly exceeds the typical extinction rate. Earth is currently going through its sixth mass extinction, which has been named the ‘Holocene extinction’.
The Holocene extinction period began in approximately c. 10,000 BCE, however extinctions are currently occurring at over 100 times the natural rate. Species that have already gone extinct in this period include the dodo, thylacine, and Western black rhino.
The Holocene epoch is considered the most detrimental extinction crisis since the dinosaurs were wiped out.
Whilst some scientists believe that there has been as many as twenty mass extinctions the ‘Big Five’, listed below, remains the most popular way of classifying Earth’s previous mass extinctions:
443 million years ago: Ordovician-Silurian
360 million years ago: Late Devonian
252 million years ago: Permian-Triassic
201 million years ago: Triassic-Jurassic
66 million years ago: Cretaceous-Tertiary
Mass extinctions do not happen out of the blue; they are the result of a number of factors. When a biosphere that is suffering long-term stress is filled with highly diverse life it amplifies the short-term events we commonly associate with mass extinctions like asteroid impacts, falling sea-levels, large-scale volcanic activity, global cooling, and global warming. Each factor on its own is not enough to cause a mass extinction, but when combined, it can result in the large-scale effects observed.
So far, the planet has recovered from all of its mass extinctions. For example, the Permian-Triassic event killed over 90% of species on the planet and even though it took an estimated 30 million years to recover, the recovery did happen. Further, mass extinctions can also accelerate the evolution of life because when dominant groups of species become extinct it makes way for new species. After the Permian-Triassic extinction hardier plants took over from other plants that were unable to adapt to the changing conditions.
So if mass extinctions have been happening for millions of years and eventually they all have balanced themselves out, what’s the problem now? Why should we care about the Holocene extinction?
Unlike the previous five extinctions the Holocene is the result of human activity, such as human-caused global warming, overfishing and contamination, and habitat destruction. Other related activities include deforestation, hunting, pollution, and the introduction of invasive species.
This is a major problem for the majority of the species on the planet, including us. For one, biodiversity and ecosystem services are worth $145 trillion globally. They are utilised for medication, crop pollination, water purification and oxygenation of the atmosphere. If the current rate of extinction continues, we will be deprived of many ecological benefits within as little as three human lifetimes. This loss, in terms of a human time-scale, is permanent.
In order to slow down or avoid this mass extinction it would require humans to intensify conservation efforts, put less pressure on the environment by reducing habitat loss and the overexploitation of resources, and actively combat climate change.
But this isn’t all. Just because humans are populous and able to inhabit many varied geographic locations does not give us immunity. According to a recent study species that are more geographically widespread are just as likely to become extinct during mass extinctions than species that occupy smaller, niche environments. This belief is based on the fact that crocodile-like animals became extinct during the Permian-Triassic event, and dinosaurs, which were rarer and less widespread, became the most prevalent species on the planet for the next 150 million years.
However, if a mass extinction were to take place, and the planet took millions of years to recover, it is unlikely that the human species would be entrusted with the task of rebuilding it given our track record… that is, if any of us survived.