The recent observations from researchers have raised alarms about the sixth mass extinction currently underway. This environmental threat to the existence of civilisation refers to a significant increase in the rate of extinction or when Earth loses more than 75% of its species in a geologically short period of time. For the context, a short geological period of time equates to less than 2.8 million years since life first evolved on the planet.
History of Mass Extinctions
The Earth has already been through five major mass extinctions.
First Mass Extinction: End Ordovician, 444 million years ago
This event led to a loss of approximately 86% of species. It was most likely caused by a severe ice age that lowered sea levels, possibly triggered by the uplift of the Appalachians. The newly exposed silicate rock sucked CO2 out of the atmosphere, causing a drop in temperatures.
Second Mass Extinction: Late Devonian, 383-359 million years ago
About 75% of species were lost during this event. The emergence of land plants and their deep roots stirred up the earth, releasing nutrients into the ocean. This may have triggered algal blooms which depleted oxygen from the water, suffocating bottom dwellers such as the trilobites.
Third Mass Extinction: End Permian, 252 million years ago
This is the most severe mass extinction on record with 96% of species being wiped out. A cataclysmic eruption near Siberia blasted CO2 into the atmosphere, and methanogenic bacteria responded by releasing methane, a potent greenhouse gas. This led to increased global temperatures, ocean acidification, and stagnation.
Fourth Mass Extinction: End Triassic, 201 million years ago
In this event, 80% of species disappeared with no apparent cause discovered so far.
Fifth Mass Extinction: End Cretaceous, 66 million years ago
This event, which wiped out approximately 76% of all species, was probably caused by a combination of volcanic activity, climate change and a celestial impact, most famously leading to the extinction of dinosaurs.
Background
The five mass extinctions that have occurred over the past 450 million years resulted in the destruction of 70-95% of the species of plants, animals, and microorganisms. These extinctions were caused by catastrophic environmental changes such as massive volcanic eruptions, depletion of oceanic oxygen, or asteroid collisions. The recovery from these events took millions of years.
Ongoing Sixth Mass Extinction
The current, sixth extinction event is human-induced and considered more immediate even than climate destruction. This period, also known as the Anthropocene extinction, signifies how only about 2% of all the species that ever lived are alive today. Despite this, the absolute number of species is greater than it has ever been before. This extinction phase, identified as the most severe environmental threat since the inception of agriculture over 11,000 years ago, is ongoing and permanent.
Outcomes of the Study
The study, which examined 29,400 species of terrestrial vertebrates, found that over 515 of them are on the brink of extinction. Majorities of these species are concentrated in regions like South America (30%), followed by Oceania (21%), Asia (21%) and Africa (16%). The trend of disappearing populations was traced back to the 1800s.
Impacts
Species extinction carries significant tangible impacts such as loss of crop pollination and water purification. Additionally, if the population of a species that plays a unique role in an ecosystem drops too low, it can have repercussions for other species by disrupting the food chain. Genetic and cultural variability are also jeopardised, impacting entire ecosystems and potentially causing a loss in contributions to human welfare.
The Way Forward
The recent Covid-19 pandemic is a stark reminder of the dire consequences of wildlife trade and habitat destruction. More pandemics are predicted if the current trajectory of wildlife consumption and habitat destruction continues. The loss of biodiversity may lead to declining plant production, lowered resistance to environmental perturbations such as drought, and increased variability in certain ecosystem processes including plant productivity, water use, and pest and disease cycles.
