Six Corners Of The World: What Threatens The Earth With Modern Extinction
The Earth is experiencing the sixth mass extinction of living beings. The fact that the planet was able to “recover” after the previous five does not provide insurance against failure. And even if so, we may not see a happy ending
Since 1850, that is, the beginning of the era of industrialization, the average temperature on Earth has increased by 1.1°C. Scientists believe that there is too little time left to stop this process until the heating has exceeded 1.5 ° C – this is the point of no return, after which it will be impossible to “cool down” the planet, and natural disasters will become more terrible the more the planet warms up. An additional 0.4°C increase in temperature is the most optimistic scenario. The pessimistic scenario assumes a temperature increase of 3.6°C since 1850.
Human civilizational activity, development of nature, urban development, deforestation, reduction of protected and untouched territories, soil and water pollution, irrational nature management and much more have already led to a significant reduction in biodiversity on Earth. For example, Brazil – the country with the widest diversity of animal and plant species – has already faced the risk of extinction of more than 10 thousand species of plants and animals due to deforestation of the Amazonian forests. Globally, approximately one million species of living beings are threatened by human activities.
Deforestation leads to the accumulation of carbon dioxide and increases the greenhouse effect. Global warming has already reduced the habitat of polar bears, and by 2050, ⅔ of the population of these animals may disappear .
The greenhouse effect has created free conditions for the life and reproduction of the fungus Batrachochitrium Dendrobatidis. For thirty years it has spread around the planet at a speed that is impossible for microorganisms in natural conditions. Scholars debate where exactly he started his journey. However, no one doubts that such a rapid development of new spaces is due to human activity.
Experts suggest that the international trade in reptiles has contributed to the spread of the fungus. Because of it, several species of amphibians have already died out and the overall population of frogs, toads, newts, salamanders and others continues to decline. This upsets the natural balance and can lead to an explosion in the number of insects, including mosquitoes that carry malaria, dengue, yellow fever and other diseases.
The history of life on Earth consists of the birth and death of millions of species of living beings. It is very difficult to name the exact number of mass extinctions, but they usually talk about the “big five”, which will be discussed below.
Extinctions In Earth’s History
A sharp and massive reduction in biodiversity on Earth occurred for natural reasons. The planet developed, tectonic plates shifted, the climate changed, the planet was bombarded by cosmic bodies, the composition of the atmosphere changed, etc. But only the modern, “sixth extinction” (it is also called the Holocene or Anthropocene), was provoked by the conscious activity of only one species – man.
Although “extinction” is perceived as something bad, there is a natural “background extinction”. Species of living beings disappear as the environment gradually changes, local cataclysms appear, better adapted competitors appear, the food supply is depleted, and inbreeding occurs. So, for example, the ancestors of people or competitive species disappeared: apparently, the Neanderthals were supplanted by the arrival of Homo sapiens.
There can be several reasons for mass extinction. An unexpected catastrophe led to the extinction of dinosaurs. The vast majority of scientists agree that this was due to a collision with a giant meteorite. Another example of a disaster would be volcanic activity. A sharp change in environmental conditions – emissions of gases and ash, acid rain, prolonged solar starvation – can lead to the death of established biological communities. Animals can migrate from disadvantaged areas and provoke competition with other species occupying the same ecological niche.
The introduction of alien species, such as predators, can tip the balance if their potential prey do not have some sort of defenses that make them difficult prey. Encountering no resistance from either competitors or prey, predators will drive out both. But after they have bred in “harvest time”, their population will decrease sharply as the food supply is depleted. Such a fate can befall not only predators. Plants may appear in place of the victim, and herbivores will destroy the food supply.
Extinction, especially of endemic species – that is, characteristic only for a particular area – can provoke a limited range. Inbreeding can reduce genetic diversity within a species, and this will adversely affect its fate.
And, finally, the most recent cause of extinction was a man and his activities – hunting, the reduction of the natural habitats of numerous species due to the construction of roads, and cities, the development of agriculture and industry, global warming, which leads to the melting of glaciers, uncontrolled fishing, pollution environment, creation of test sites for weapons testing, large-scale military exercises, garbage disposal, etc.
All causes of extinction are closely related and can provoke each other. In particular, this is why it is so difficult for scientists to isolate one specific key cause of each of the past extinctions: it sets off a chain reaction. And in conditions of catastrophes, the impact of existing adverse factors can increase many times over.
Extinction Number Zero
The oxygen catastrophe is not one of the “big five” extinctions, but it is the earliest biodiversity loss event on the planet. Due to the paucity of material sources for its study (then the Earth was inhabited by unicellular organisms, which left only indirect evidence about themselves), very little is known about it. This event occurred approximately 2.4–2 billion years ago and is associated with the saturation of the Earth’s atmosphere with molecular oxygen (O 2 ).
It is believed to have been produced by cyanobacteria. A change in the chemical composition of the atmosphere led to the fact that a significant number of species of anaerobic (that is, receiving energy in the absence of oxygen) bacteria died.
However, anaerobic life forms, including bacteria, still live today. For example, Clostridium botulinum ( Clostridium botulinum ) is well known for the toxin it produces. Botulinum toxin or “Botox” is the strongest organic poison, but in extremely small doses it is used in cosmetology.
Botulinum toxin or Botox, one of the strongest poisons (Photo: Wikimedia)
Other anaerobic organisms living on a planet with an oxygen-rich atmosphere are, for example, parasitic helminth worms, some types of fungi ( for example , ruminal and intestinal fungi of herbivores), plants, algae.
The First Extinction – But Not In Scale
The Ordovician-Silurian is considered the first mass extinction of the “big five”. It took place in two stages with an interval of 1 million years approximately 440-450 million years ago. It is believed that one of its causes was another and rather strong ice age, which was especially destructive since the level of the world ocean was relatively low.
There are suggestions that the cooling was caused by the Earth falling into a cloud of cosmic dust formed as a result of the destruction of a large (about 150 km in diameter) asteroid. In the second stage of the Ordovician-Silurian extinction, the oxygen content in the world’s oceans probably dropped to almost zero. Since all known life lived in the seas and oceans, this led to the death of about 85% of animal species.
All numerical estimates of mass extinctions are approximate. No matter how devastating for biodiversity the figures of species loss may seem, we must remember that we cannot state the knowledge of the entire breadth of the species diversity of flora and fauna, especially unicellular organisms.
The Second Extinction Is Long
The Devonian extinction led to the loss of about 75% of the species of living beings. The event began approximately 374 Ma ago and continued with variable intensity for about 20–25 Ma. Scientists identify from 8 to 10 stages in this process, of which two are the most disastrous: the “Kellwasser event” that opens the Devonian extinction and the “Hangenberg event” that completes it, lying on the border of the Devonian and Carboniferous periods.
The causes of the Devonian extinction are not exactly known – only a change in environmental conditions can be stated. There is evidence of anoxia in the waters of the World Ocean and its glaciation by the end of the extinction event.
The Third Extinction Is The Best
The third extinction – Permian – is the most massive in the geological history of the Earth. By the way, the geological Permian period, after which the extinction event is named, was named by the British geologist Roderick Murchison in honor of the Perm province, where he found previously unknown geological formations .
The exact causes of extinction are unknown. Both catastrophes (collision with an asteroid, release of methane from the bottom of the sea, change of poles) and gradual changes in the environment (release of methane as a waste product of archaea, gradual increase in temperature and dryness of the climate, changes in the composition of the atmosphere, in particular, anonxia, reduction share of oxygen).
The most probable cause is considered to be the outpouring of the Siberian traps approximately 251 million years ago. Traps are a special type of continental magmatic outpouring. Huge volumes of molten basalt pour to the surface in a relatively short (from a geological point of view) time and form staircase-like (hence the name) formations. The largest trap provinces in the world are Icelandic (second) and Siberian (largest), which stretches from the Urals in the west to the East Siberian Mountains in the east (approximately to Yakutsk) and from about the latitude of Novosibirsk to the coast of the Arctic Ocean.
Such colossal volcanic activity could provoke a volcanic winter, a greenhouse effect and other changes that had a detrimental effect on the biosphere. By comparison, 1816, the ” year without a summer “, was triggered by the eruption, albeit one of the largest in documented history, but of only one Tambora volcano in Indonesia in 1815. The Permian extinction was fatal for 96% of marine species, 73% of terrestrial vertebrate species and 83% of insect species. Biodiversity is thought to have taken 4–10 to 30 Ma to recover from the Permian extinction.
The Fourth Extinction Is Mysterious
The Triassic-Jurassic extinction liberated ecological niches, which were then occupied by dinosaurs. This event occurred 201.3 million years ago and led to the extinction of 76% of the species. But there is still no hypothesis that would answer all questions about the causes of extinction.
Among the main culprits are volcanic activity and carbon dioxide emissions. Asteroid impacts may have contributed to the extinction. Although no impact crater has been found to match the extinction chronology, the biosphere may have degraded gradually due to earlier impacts. It is hypothesized that emissions of carbon dioxide and sulfur dioxide due to volcanic activity in the Central Atlantic Igneous Province played a key role in this extinction.
The Fifth Extinction Is The Most Famous
The last and perhaps the most famous extinction is the Cretaceous-Paleogene one, which happened 66 million years ago as a result of an asteroid impact and lasted about 30 thousand years after the catastrophe. This extinction ended the age of the dinosaurs and brought large mammals to the fore. Dinosaurs did not disappear without a trace: some of their descendants are birds. 66 million years ago, about one-sixth of all species died out, but megafauna was mainly affected – almost no animal heavier than 25 kg (with rare exceptions in the form of ancestors of sea turtles and crocodiles) survived.
Modern Extinction, Sixth
The mass Holocene (the name of the current geological stage) or Anthropocene extinction, which began about 500 years ago, is exclusively the result of human activity. Current extinction rates are estimated to be 100 or even 1000 times the natural background rate. Mass extinction affects many orders and species of flora and fauna: mammals, birds, amphibians, reptiles, fish, and invertebrates.
It is assumed that anthropogenic impact on the environment, degradation of habitats, and the disappearance of many species of macroscopic fauna have led to the undocumented disappearance of many species of bacteria, archaea, and protozoa, which science simply was not aware of.
From an ecological point of view, man is an unprecedented global super-predator. It not only competes with other large predators but also systematically hunts and exterminates them. And it affects food chains everywhere. The first victims of the sixth extinction fell precisely because of hunting. Recently, the priority has shifted towards the violation of natural habitats – the drainage of swamps, deforestation, pollution of the world’s oceans, the extraction and use of natural resources, the construction and expansion of cities, and means of communication due to human settlement over vast territories.
A 2021 study showed that only 3% of the earth’s surface can be considered untouched by humans: healthy populations of native animal species remain there. Such areas may include, for example, highlands.
The 2019 Global Assessment Report on Biodiversity and Ecosystem Services stated that about 1 million species of living things are threatened with extinction due to human activities. And each year, updated information on the rate of biodiversity decline reveals that earlier estimates were more optimistic. Scientists insist that the situation is getting worse and worse – about 30% of the species are endangered.
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