{"id":851,"date":"2024-09-29T13:07:14","date_gmt":"2024-09-29T10:07:14","guid":{"rendered":"https:\/\/planeta21vek.ru\/artemiada\/eng\/?p=851"},"modified":"2025-11-20T19:41:00","modified_gmt":"2025-11-20T16:41:00","slug":"six-mass-extinctions-in-earths-history-are-we-on-the-brink-of-a-seventh","status":"publish","type":"post","link":"https:\/\/planeta21vek.ru\/artemiada\/eng\/2024\/09\/29\/six-mass-extinctions-in-earths-history-are-we-on-the-brink-of-a-seventh\/","title":{"rendered":"Six Mass Extinctions in Earth’s History. Are We on the Brink of a Seventh?"},"content":{"rendered":"

Scientists define a mass extinction as the extinction of about three-quarters of all species over a short geological period of time, which is less than 2.8 million years, according to The Conversation. Right now, humans are at the beginning of the last mass extinction, which is moving much faster than any other. Since 1970, vertebrate species populations have declined by an average of 68%, and more than 35,000 species are currently considered threatened with extinction, according to the International Union for Conservation of Nature (IUCN). During the 20th century alone, about 543 species of land vertebrates became extinct, according to a research paper in the journal PNAS.<\/p>\n

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Fossils not only tell us what creatures came before us, but also how long a species can naturally survive before it goes extinct without human intervention. This is called the background rate, and it is about one extinction per 1 million species per year. Currently, due to human activity, the actual background rate is tens of thousands of times higher, meaning species are going extinct much faster than they should. Research has shown that some species that have disappeared from Earth would have continued to exist for 800 to 10,000 years without human intervention, according to a study published in the journal Science Advances.<\/p>\n

Scientists have discovered a hidden mass extinction in Earth’s ancient past in 2022.<\/strong>\u00a0<\/span>New evidence suggests that a global drop in oxygen levels about 550 million years ago led to Earth’s first known mass extinction.<\/p>\n

The height of the Ediacaran period, about 550 million years ago, was a time when life flourished in Earth\u2019s oceans. Feather-shaped peltatonamides sucked nutrients from the water, slug-like kimberellas grazed on microbial mats, and the ancestors of jellyfish were just beginning to make waves.<\/p>\n

However, then 80% of life on Earth disappeared, leaving no trace in the fossil record.<\/p>\n

Now, a new study suggests that these missing fossils point to Earth\u2019s earliest known mass extinction event. These first communities of large, complex animals were killed by a sharp global decline in oxygen \u2014 a discovery that could have implications for modern ocean ecosystems threatened by human activity.<\/p>\n

“This represents the oldest recognized major extinction in the animal fossil record,” said lead study author Scott Evans, a research scientist at Virginia Tech. “It’s consistent with all major mass extinctions because it’s associated with climate change.”<\/p>\n

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\nImprints of the extinct Ediacaran fossils Dickinsonia (left) and the related but rare form Andiva (right) from Nilpena Ediacara National Park in South Australia. Scott Evans<\/em><\/p>\n

Animals have gone through the evolutionary crucible of mass extinctions at least five times. There were the Ordovician-Silurian and Devonian extinctions (440 million and 365 million years ago, respectively), which wiped out many marine organisms. Then there were the Permian-Triassic \u2014 also known as the Great Dying \u2014 and the Triassic-Jurassic extinctions (250 million and 210 million years ago, respectively), which affected marine vertebrates and land animals. The most recent mass extinction, about 66 million years ago at the end of the Cretaceous Period, wiped out about 75% of plants and animals, including non-avian dinosaurs.<\/p>\n

Whether another mass extinction should be added to this list has been an open question among paleontologists for some time. Scientists have long known about a sudden drop in fossil diversity 550 million years ago, but it was unclear whether it was due to a sudden mass extinction event.<\/p>\n

One possible explanation is that early trilobites \u2014 armored, often helmeted marine arthropods \u2014 began to compete with the Ediacaran fauna, causing the latter to go extinct. Another possible explanation is that the Ediacaran fauna continued to exist, but the conditions needed to preserve Ediacaran fossils did not last until 550 million years ago. \u201cPeople recognized that there was a change in the biota at that time,\u201d Evans said. \u201cBut there were significant questions about what the causes might have been.\u201d<\/p>\n

To answer these questions, Evans and his colleagues compiled a database of Ediacaran fossils that other researchers had previously described in the scientific literature, sorting each entry by factors such as geographic location, body size, and diet. The team catalogued 70 genera of animals that lived 550 million years ago and found that only 14 of those genera were still around 10 million years later. They didn\u2019t see any significant changes in the conditions needed to preserve the fossils, nor did they find differences in diet that would suggest that the Ediacaran animals went extinct due to competition with early Cambrian animals like trilobites.<\/p>\n

But the surviving organisms had one thing in common: body plans with a large surface area relative to volume, which may help the animals cope with low-oxygen conditions. This observation, combined with geochemical evidence of declining oxygen levels 550 million years ago, suggests that the Ediacaran period may have ended with a mass extinction caused by low oxygen in the ocean. The researchers published their findings online Nov. 7, 2022, in the journal Proceedings of the National Academy of Sciences.<\/p>\n

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\nImprints of extinct Ediacaran fossils Dickinsonia (centre) and the smaller anchor-shaped Parvancorina (left) in sandstone at Nilpena Ediacara National Park in South Australia. Scott Evans<\/em><\/p>\n

\u201cWe looked at patterns of selectivity \u2014 what went extinct, what survived, and what thrived after the extinction,\u201d said study co-author Shuhai Xiao, a professor of geobiology at Virginia Tech. \u201cIt turns out that organisms that can\u2019t cope with low oxygen levels were selectively eliminated.\u201d<\/p>\n\n

Why oxygen levels dropped sharply in the final years of the Ediacaran period remains a mystery. Evans said volcanic eruptions, plate tectonics and asteroid impacts are possible, as are less dramatic explanations such as changing nutrient levels in the ocean.<\/p>\n

Regardless of how exactly it happened, this mass extinction likely influenced the subsequent evolution of life on Earth and may have implications for scientists studying how animal life originated.<\/p>\n

“The Ediacaran animals are pretty weird \u2014 most of them look nothing like the animals we know,” Evans said. “After this extinction, we start seeing more and more animals that look like the ones we have today. It’s possible that this early event paved the way for more modern animals.”<\/p>\n

The results may also contain lessons about the threats humans pose to aquatic life. Various agricultural and wastewater discharges have introduced nutrients such as phosphorus and nitrogen into marine and river ecosystems, increasing the amount of algae that decompose in the water and consume oxygen. The spread of \u201cdead zones,\u201d where oxygen levels in the water are too low to support life, may pose similar problems for modern animals.<\/p>\n

Ordovician\u2013Silurian extinction event: 440 million years ago, 85% of species went extinct.<\/strong>\u00a0<\/span>Earth\u2019s next mass extinction occurred during a period when organisms like corals and armored brachiopods filled the world\u2019s shallow waters but had not yet moved onto land. Life itself had begun to spread and diversify, first appearing about 3.7 billion years ago. But about 440 million years ago, a climate shift changed sea temperatures, and most ocean life died.<\/p>\n

At the end of the Ordovician period, a rapid onset of massive glaciation covered the southern supercontinent of Gondwana. Glaciation on this scale locked up a large percentage of the world’s waters and dramatically lowered sea levels, depriving many species of vital habitats, disrupting food chains, and reducing reproductive success, according to a study published in the journal Oceanology.<\/p>\n

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It is not known exactly what caused these events. One theory is that the cooling process may have been triggered by the formation of the North American Appalachian Mountains, according to Ohio State News. The massive erosion of these silicate rocks is associated with the removal of the greenhouse gas carbon dioxide from the atmosphere.<\/p>\n

However, not all scientists agree. Alternative theories suggest that the toxic metal may have dissolved into ocean waters during a period of oxygen depletion, killing off marine life, according to National Geographic. Other scientists suggest that a gamma-ray burst from a supernova tore a huge hole in the ozone layer, allowing deadly ultraviolet radiation to kill life below, according to APS News, and another theory suggests that volcanism was the culprit, according to a study published in the journal Geology.<\/p>\n

Late Devonian extinction: 365 million years ago, 75% of species went extinct.<\/strong><\/span>\u00a0<\/span>Often called the \u201cAge of Fishes,\u201d the Devonian period saw the rise and fall of many prehistoric marine species. Although animals had begun to evolve on land by this time, most life swam in the oceans. That is, until vascular plants, such as trees and flowers, likely caused the mass extinction, according to a 1995 study published in the journal GSA Today.<\/p>\n

According to the BBC, as the plants developed roots, they inadvertently transformed the land they lived on, turning rocks and rubble into soil. This nutrient-rich soil then ended up in the world\u2019s oceans, causing algae blooms on a massive scale. These blooms essentially created giant \u201cdead zones,\u201d which are areas where algae suck oxygen out of the water, suffocating marine life and damaging marine food chains. Species that couldn\u2019t adapt to the reduced oxygen levels and lack of food died.<\/p>\n

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However, this theory is disputed, and some scientists believe that volcanic eruptions are to blame for the decline in ocean oxygen levels, according to a study published in the journal Geology.<\/p>\n

One of the sea monsters that was wiped off the face of the earth was a 10-meter-long armored fish called Dunkleosteus. A fearsome predator, this giant fish had a helmet of bony plates that covered its entire head and created a fang-like protrusion on its jaw.<\/p>\n

Permian\u2013Triassic extinction event: 253 million years ago, 96% of marine life died out; 70% of land life died out.<\/strong><\/span>\u00a0<\/span>Often called the \u201cGreat Dying,\u201d this extinction event is the largest to ever occur on Earth. It wiped out about 90% of all the planet\u2019s species and wiped out the reptiles, insects, and amphibians that roamed the land. The cause of this catastrophic event was, according to one theory, a period of rampant volcanism. At the end of the Permian period, volcanoes erupted in the part of the world we now call Siberia. This released large amounts of carbon dioxide into the atmosphere, causing a greenhouse effect that heated the planet. This changed weather patterns, raised sea levels, and brought acid rain to the land.<\/p>\n

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In the ocean, elevated levels of carbon dioxide dissolved into the water, poisoning marine life and depriving it of oxygen-rich water, according to the Sam Noble Museum in Oklahoma. At the time, the world consisted of a single supercontinent called Pangea, which some scientists believe contributed to the lack of movement in the world’s oceans, creating a global pool of standing water that only perpetuated the accumulation of carbon dioxide. Rising sea temperatures also reduced oxygen levels in the water.<\/p>\n\n

Triassic\u2013Jurassic extinction event: 201 million years ago, 80% of species went extinct.<\/strong>\u00a0<\/span>The Triassic period saw the emergence of new and diverse life, and dinosaurs began to populate the world. Unfortunately, numerous volcanoes were erupting at the same time. While it\u2019s unclear exactly why this fourth mass extinction occurred, scientists believe that massive volcanic activity occurred in an area of \u200b\u200bthe world now covered by the Atlantic Ocean, according to MIT News. Like the Permian extinction, the volcanoes released massive amounts of carbon dioxide, which changed the climate and wiped out life on Earth. Global temperatures rose, ice melted, and sea levels rose and became acidic. As a result, many marine and land species became extinct, including large prehistoric crocodiles and some flying pterosaurs.<\/p>\n

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According to Discover magazine, there are alternative theories to explain this mass extinction, suggesting that rising carbon dioxide levels led to the release of trapped methane from permafrost, which could have triggered a similar series of events.<\/p>\n

K-Pg extinction: 66 million years ago, 75% of species went extinct.<\/strong>\u00a0<\/span>The most famous of all mass extinctions is the Cretaceous-Paleogene extinction event \u2013 \u200b\u200bbetter known as the day the dinosaurs died out. This event is sometimes also called the K-T extinction, and geologists call it the \u201cK-Pg extinction\u201d because the \u201cC\u201d is short for the previous geological period called the Cambrian. The \u201cK\u201d comes from the German word \u201cKreide,\u201d meaning \u201cCretaceous.\u201d<\/p>\n

An asteroid more than 8 miles (13 kilometers) in diameter slammed into Earth at about 45,000 miles per hour (72,000 km\/h), crash-landing in what is now Yucatan, Mexico. It punched a hole 110 miles (180 km) wide and 12 miles (19 km) deep, called the Chicxulub crater. The impact would have scorched all the land around it for a radius of 900 miles (1,450 km) and ended the 180-million-year reign of the dinosaurs on Earth.<\/p>\n

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The impact left blackened skies for months as debris and dust were thrown into the atmosphere. This prevented plants from absorbing sunlight, causing them to die off en masse, disrupting the dinosaurs\u2019 food chains. It also caused global temperatures to plummet, plunging the world into a long, cold winter. Scientists estimate that most extinctions on Earth at the time would have occurred within months of the impact. However, many species that could fly, burrow, or dive into the deep oceans survived. For example, the only true descendants of dinosaurs alive today are modern birds \u2013 more than 10,000 species are thought to have descended from impact survivors.<\/p>\n\n","protected":false},"excerpt":{"rendered":"

Scientists define a mass extinction as the extinction of about three-quarters of all species over a short geological period of time, which is less than 2.8 million years, according to The Conversation. Right now, humans are at the beginning of the last mass extinction, which is moving much faster than any other. Since 1970, vertebrate species populations have declined by an average of 68%, and more than 35,000 species are currently considered threatened with extinction, according to…<\/p>\n

Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":852,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[249,225,283,324,280,219,290,323,326,327],"tags":[345,348,253,347,346],"class_list":{"0":"post-851","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-antropologia","8":"category-archeology","9":"category-melovoi","10":"category-devon","11":"category-ediakar","12":"category-history","13":"category-noveishee","14":"category-ordovik","15":"category-permper","16":"category-trias","17":"tag-carbon-dioxide","18":"tag-dead-zones","19":"tag-extinction","20":"tag-icing","21":"tag-volcanoes"},"_links":{"self":[{"href":"https:\/\/planeta21vek.ru\/artemiada\/eng\/wp-json\/wp\/v2\/posts\/851","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/planeta21vek.ru\/artemiada\/eng\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/planeta21vek.ru\/artemiada\/eng\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/planeta21vek.ru\/artemiada\/eng\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/planeta21vek.ru\/artemiada\/eng\/wp-json\/wp\/v2\/comments?post=851"}],"version-history":[{"count":4,"href":"https:\/\/planeta21vek.ru\/artemiada\/eng\/wp-json\/wp\/v2\/posts\/851\/revisions"}],"predecessor-version":[{"id":1429,"href":"https:\/\/planeta21vek.ru\/artemiada\/eng\/wp-json\/wp\/v2\/posts\/851\/revisions\/1429"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/planeta21vek.ru\/artemiada\/eng\/wp-json\/wp\/v2\/media\/852"}],"wp:attachment":[{"href":"https:\/\/planeta21vek.ru\/artemiada\/eng\/wp-json\/wp\/v2\/media?parent=851"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/planeta21vek.ru\/artemiada\/eng\/wp-json\/wp\/v2\/categories?post=851"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/planeta21vek.ru\/artemiada\/eng\/wp-json\/wp\/v2\/tags?post=851"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}