A sixth mass extinction? New research says we are living through it right now!10 min readReading Time: 7 minutes
What do these creatures have in common?
If you guessed ‘they are all extinct’, you are absolutely right! But don’t get excited just yet, this article doesn’t exactly paint a rosy picture.
Our planet Earth has witnessed five mass extinctions in the past, with the last one about 65 million years wiping out the dinosaurs. Many experts have warned in the recent past that a sixth mass extinction crisis is underway, and a new study has now added that the Earth could have already lost about 7.5 and 13% of its total species! Yes, we told you this article wasn’t all good news!
“Drastically increased rates of species extinctions and declining abundances of many animal and plant populations are well documented, yet some deny that these phenomena amount to mass extinction,” said Robert Cowie, lead author of the study and research professor at the UH Manoa Pacific Biosciences Research Center in the School of Ocean and Earth Science and Technology.
The definition of a mass extinction
Before we move forward, let’s get some basics in place. Extinction is a part of life, and animals and plants disappear all the time — such is the circle of life. About 98% of all the organisms that have ever existed on our planet are now extinct!
When a species goes extinct, its role in the ecosystem is usually filled by new species, or other existing ones that adapt accordingly. Earth’s ‘normal’ extinction rate is often thought to be somewhere between 0.1 and 1 species per 10,000 species per 100 years. This is known as the background rate of extinction.
A mass extinction event is when species vanish much faster than they are replaced. This is usually defined as about 75% of the world’s species being lost in a ‘short’ amount of geological time — less than 2.8 million years.
What was the study all about?
Now that we understand what a mass extinction is, let’s get back to the study. The research team studied molluscs (land snails and slugs), the second-largest phylum (a major group of animals or plants) in numbers of known species. According to the IUCN Red List (defined below) data, molluscs have suffered a higher rate of extinction than birds and mammals. Invertebrates constitute about 95% of known animal species and it is, therefore, essential to include them in the biodiversity extinction estimate, say researchers. However, among the 1.5 million described species of invertebrates, only less than 2 per cent have been fully evaluated and many remain in the ‘Data Deficient’ category. This essentially means that most species have not been studied.
The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, founded in 1964, is the world’s most comprehensive inventory of the global conservation status of biological species. It uses a set of criteria to evaluate the extinction risk of species and subspecies.
Gathering the results from the molluscs, the team wrote that since 1500 about 1,50,000 to 2,60,000 of all the known species have gone extinct. But according to the IUCN, only 882 species are listed as extinct.
The paper, published in Biological Reviews, stressed that “humans are the only species able to manipulate the Earth on a grand scale, and they have allowed the current crisis to happen.”
Owliver’s Obscure Observations
A Pulitzer Prize-winning book ‘The Sixth Extinction: An Unnatural History’ said that this (the current mass extinction) is the first such event to be caused entirely by humans.
“We are not just another species evolving in the face of external influences. In contrast, we are the only species that has conscious choice regarding our future and that of Earth’s biodiversity,” said Cowie.
Depending on where you look, however, some species are faring better than others in the current crisis, the researchers point out, with marine species extinctions and plant extinctions not yet looking as grave as the rate of extinctions seen in many land animals.
A scary prediction
Increasing carbon levels in the oceans may lead to the sixth mass extinction in Earth’s history by about 2100, Massachusetts Institute of Technology (MIT) scientists predicted after analysing data from the last 540 million years. Researchers analysed significant changes in the carbon cycle over the last 540 million years, including the five mass extinction events.
The carbon cycle is a process where carbon dioxide travels from the atmosphere into living organisms and the Earth, then back into the atmosphere.
They identified “thresholds of catastrophe” in the carbon cycle that, if exceeded, would lead to an unstable environment, and ultimately, mass extinction.
Researchers proposed that mass extinction occurs if one of two thresholds are crossed. First, the changes in the carbon cycle that occur over long timescales – extinctions will follow if those changes occur at rates faster than global ecosystems can adapt, they said.
So what caused earlier extinctions?
There have been several theories about why earlier mass extinctions happened. Before the Cretaceous mass extinction, known for wiping out dinosaurs, the Earth had witnessed four other great mass extinctions. A paper published in the journal, Nature Geoscience, came up with a new reason behind the first mass extinction, also known as the Late Ordovician mass extinction. The research paper notes that the cooling climate likely changed ocean patterns. This caused a disruption in the flow of oxygen-rich water from the shallow seas to deeper oceans, leading to a mass extinction of marine creatures.
The big extinction events were:
- The Ordovician-Silurian mass extinction occurred 443 million years ago and wiped out approximately 85% of all species. Scientists think it was caused by temperatures going down and huge glaciers forming, which caused sea levels to drop dramatically. This was followed by a period of rapid warming. Many small marine creatures died out.
- The Devonian mass extinction event took place 374 million years ago and killed about three-quarters of the world’s species, most of which were marine invertebrates that lived at the bottom of the sea. This was a period of many environmental changes, including global warming and cooling, a rise and fall of sea levels and a reduction in oxygen and carbon dioxide in the atmosphere. We don’t know exactly what triggered the extinction event.
- The Permian mass extinction, which happened 250 million years ago, was the largest and most devastating event of the five. Also known as the Great Dying, it eradicated more than 95% of all species, including most of the vertebrates which had begun to evolve by this time. Some scientists think Earth was hit by a large asteroid which filled the air with dust particles that blocked out the Sun and caused acid rain. Others think there was a large volcanic explosion which increased carbon dioxide and made the oceans toxic.
- The Triassic mass extinction event took place 200 million years ago, eliminating about 80% of Earth’s species, including many types of dinosaurs. This was probably caused by major geological activity that increased carbon dioxide levels and global temperatures, as well as ocean acidification.
- The Cretaceous mass extinction event occurred 65 million years ago, killing 78% of all species, including the remaining non-avian dinosaurs. This was most likely caused by an asteroid hitting the Earth in what is now Mexico.
Can we stop a sixth mass extinction?
Mass extinctions are a large and complex issue. They can happen extremely slowly, taking millions of years to unfold, but right now, it seems likely we are experiencing a sixth, and it is undoubtably the result of human actions.
Experts say that if we can all work together on reducing the negative impact we’ve had on the climate, then other things will also improve, such as the number of species that are currently threatened by habitat loss.
Many believe the changes we need to see now can be achieved fastest by prioritising the protection and preservation of nature. Experts say that rather than putting pressure on individuals, pressure should be put on policymakers and businesses to reduce harmful carbon emissions.
Human activities such as the burning of oil, coal and gas, as well as deforestation are the primary cause of the increased carbon dioxide concentrations in the atmosphere.
However, we all have an active role to play in saving our planet, and this requires a deep transformation of our values, attitudes and behaviours. Do you agree?
Sources: Indian Express, Science Alert, National Geographic