Source: Academic Headlines
At present, severe global ecological and environmental issues have become international issues, whether it is greenhouse gas emissions, pollution control, or biodiversity issues, which are topics closely related to the public.
In particular, the news that the sixth mass extinction is coming is worrying.
So, is this true or false, and is there any scientific basis for it?
Recently, a team of biologists from the University of Hawai'i at Mānoa and the Muséum National d'Histoire Naturelle in Paris, France, conducted a study on the "sixth mass extinction" and found that 7.5%-13% of the 2 million known species on Earth since 1500; Island species are much more affected than continental species.
As a result, experts believe that the sixth mass extinction has already begun to occur, and unlike the previous five, which was caused by extreme natural phenomena, this mass extinction was caused by human activities.
The related research paper is titled "The Sixth Mass Extinction: Fact, Fiction or Speculation?" It was published in the scientific journal Biological Reviews.
The "Sixth Mass Extinction" is underway
Mass extinction refers to the mass extinction of species in a short period of time, and once it occurs, it is often the extinction of many different biological groups together. Large-scale cluster extinctions have a certain periodicity, occurring about once every 62 million years, and it is now recognized that there have been five mass extinctions on Earth, when humans have not yet appeared.
Now, many biologists say that humanity is likely to suffer such a "catastrophe."
To investigate whether the "sixth mass extinction" is taking place, the team focused on the extinction of invertebrate species, which account for 95-97% of known animal species. In addition, they argue that many species on Earth may have gone extinct before they were even discovered by humans, and that invertebrates would leave their shells behind even after death, so surveys of them would yield more convincing evidence and statistics.
Figure | Shells left by the recently extinct land snails of Rurutu (Southern Polynesia Archipelago of French Polynesia). (Source: The paper)
Thus, by extrapolating the number of species of land snails and slugs, the researchers found that of the 2 million species known on Earth since 1500, about 150,000 to 260,000 species have become extinct, accounting for 7.5%-13% of the total number of species! This figure is much larger than the 882 (0.04%) published by the International Union for Conservation of Nature (IUCN).
It can be seen that the extinction of species on Earth may be far more serious than people think. "This study has uncovered mass extinctions of invertebrates, which is key to our confirmation of the beginning of the sixth mass extinction in Earth's history." First author Robert H. Cowie, a research professor at the Pacific Center for Biological Sciences in the School of Ocean and Earth Sciences and Technology (SOEST), said.
However, the situation is not the same in different regions. For example, the researchers found that despite the current significant threat to marine species, there is no evidence that the crisis has affected the oceans to the same extent as on land.
In addition, island species, such as the Hawaiian Islands, are much more affected than mainland species, and plants appear to be becoming extinct at a lower rate than terrestrial animals.
Is it alarmist? Or is there evidence to follow?
However, there is also controversy over whether the "sixth mass extinction" has begun.
It has been argued that the currently declared rate of extinction is not significantly greater than the rate of natural extinction (i.e., the natural extinction of species), and therefore cannot be said to be a mass extinction. However, researchers have shown in the paper that according to this statistic, the current species extinction rate has reached 150-260 E/MSY (that is, 150-260 per million species will go extinct each year), which is far greater than the 2 E/MSY natural extinction rate measured by previous scientists!
The Red List, listed by the International Union for Conservation of Nature (IUCN) in 2020, is widely regarded as the most comprehensive compilation of the state of conservation of plants and animals worldwide, and many scientists rely on the data on this list to argue that the "sixth mass extinction" is far from coming.
However, the team found that the list mainly covers amphibians, birds, and mammals, which may be biased compared to other historically studied species classifications.
Figure | There is a bias in the categories of species on the Red List. (Left) The total number of species in the selected major vertebrate and invertebrate populations from two scientific papers from 2019 and 2021 differs significantly from the proportion of these species assessed on the (right) Red List. (Source: The paper)
As Professor Cowie puts it: "The sharp rise in extinction rates and the decline in population abundance in many flora and fauna is well documented, but some people do not believe in the link between these phenomena and mass extinction, and this denial is actually based on prejudice against the crisis, focusing only on mammals and birds, ignoring invertebrates." ”
In addition, it is also believed that species decline is a new natural evolutionary trajectory, because humans are also one of the species and have also played a natural role in the history of the earth. However, Cowie emphasizes: "Humans are the only species capable of manipulating the biosphere on a large scale, and we are more than just a species that has evolved under external influences." In contrast, we are the only species that consciously chooses our future and the biodiversity of the planet. ”
Five mass extinctions have occurred on Earth
Historically, earth has experienced many mass extinction events that have had a huge impact on biodiversity, the most famous of which are five:
The first was the Ordovician-Silurian mass extinction, which occurred 440 million years ago at the end of the Ordovician period, and about 85% of species went extinct. Supernova explosions near Earth produce gamma-ray bursts that destroy Earth's ozone layer, causing massive deaths of marine plankton, the destruction of the foundations of the food chain, and a great famine. Primitive fish survived and gradually replaced invertebrates dominating the ocean.
The second was a late Devonian mass extinction, occurring 370 million years ago, when about 75% of marine life went extinct. The culprits of this mass extinction came from inside the Earth — the eruption of the Super Mantle Column. 300 billion cubic meters of magma are gushing out of the ground, and the seawater is severely polluted.
Figure | The overlord of the late Devonian period, the Dunn's fish, is 11 meters long, weighs more than 4 tons, and has a bite force of 5 tons (source: bing.com)
The third is the Permian-Triassic mass extinction, which occurred at the end of the Permian, at the junction of the Paleozoic and Mesozoic eras, and 258 to 252 million years ago, supervolcano eruptions caused 90-96% of species to go extinct, of which marine animals became extinct 96% and land animals became extinct 70%, the largest known extinction ever.
The fourth is the Triassic-Jurassic mass extinction, which occurred at the end of the Mesozoic Triassic, 201 million years ago, and caused 70-75% of species extinctions. This event was the dawn of the age of the dinosaurs, when early masterosaurs, most zygoteans, and large amphibians went extinct, allowing dinosaurs to take over the terrestrial world with little competition from land. Crocodiles succeeded Phyto-Long as the hegemon of freshwater ecosystems.
Figure | Extinction of the phytoosaurs at the end of the Triassic period - chisel-toothed crocodile (Source: bing.com)
The fifth is the Cretaceous-Paleogene mass extinction, which occurred at the end of the Mesozoic Cretaceous Period, 66 million years ago, and caused 75% of species extinctions. An asteroid or comet with a diameter of tens of kilometers hits the earth, the crater has a radius of up to 150 kilometers, and the dust produced is obscured by the sun, and the earth can not see sunlight for several years or even more than a decade. This mass extinction led to the extinction of dinosaurs and the rise of mammals, and was actually the least of the five mass extinctions.
Previously, some people on the Internet had commented that biodiversity should be manipulated in the interests of human beings, but after seeing so many extinction events that are older than the entire history of mankind, who can define the so-called "interests"?
So maybe our response won't have an immediate effect or reverse the overall trend of extinction, but we must continue to do miracles for nature.
Otherwise, the arrival of the sixth mass extinction will only get faster and faster.
Resources:
https://phys.org/news/2022-01-strong-evidence-sixth-mass-extinction.html
https://onlinelibrary.wiley.com/doi/10.1111/brv.12816
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