No species lasts forever \u2014 extinction is part of the evolution of life. <\/p>\n
But at least five times, a biological catastrophe has engulfed the planet, killing off the vast majority of species from water and land over a relatively short geological interval. <\/p>\n
The most famous of these mass extinction events \u2014 when an asteroid slammed into Earth 66 million years ago, dooming the dinosaurs and many other species \u2014 is also the most recent. But scientists say it won\u2019t be the last. <\/p>\n
Many researchers argue we\u2019re in the middle of a sixth mass extinction, caused not by a city-size space rock but by the overgrowth and transformative behavior of a single species <\/strong>\u2014 Homo sapiens. Humans have destroyed habitats and unleashed a climate crisis. <\/p>\n Calculations in a September study published in the journal PNAS have suggested that groups of related animal species are disappearing at a rate 35% times higher than the normally expected rate. <\/p>\n And while every mass extinction has winners and losers, there is no reason to assume that human beings in this case would be among the survivors. <\/p>\n In fact, study coauthor Gerardo Ceballos thinks the opposite could come to pass, with the sixth mass extinction transforming the whole biosphere, or the area of the world hospitable to life \u2014 possibly into a state in which it may be impossible for humanity to persist unless dramatic action is taken. <\/p>\n \u201cBiodiversity will recover but the winners (are) very difficult to predict. Many of the losers in these past mass extinctions were incredibly successful groups,\u201d said Ceballos, a senior researcher at the Institute of Ecology at the National Autonomous University of Mexico. <\/p>\n While the causes of the \u201cbig five\u201d mass extinctions varied, understanding what happened during these dramatic chapters in Earth\u2019s history \u2014 and what emerged in the aftermath of these cataclysms \u2014 can be instructive. <\/p>\n \u201cNobody\u2019s seen these events but they\u2019re on a scale that might be repeated. We\u2019ve got \u2026 (to) learn from the past because that\u2019s our only data set,\u201d said Michael Benton, a professor\u00a0of vertebrate paleontology at Bristol University in the United Kingdom who is the author of the new book \u201cExtinctions: How Life Survives, Adapts and Evolves.\u201d <\/p>\n While paleontologists have studied fossils for centuries, the science of mass extinction is relatively new. Radiometric dating, based on the natural radioactive decay of certain elements, like carbon, and other techniques revolutionized the ability to precisely determine the age of ancient rocks in the second half of the last century. <\/p>\n The developments set the stage for the work of the late Nobel Prize-winning physicist Luis Alvarez and his geologist son Walter, professor\u00a0of Earth and planetary science at the Univeristy of California, Berkeley. Along with two other colleagues, they coauthored a sensational 1980 paper about the \u201ciridium anomaly\u201d \u2014 a 1-centimeter-thick (0.4-inch-thick) layer of sedimentary rock rich in iridium, an element rare on Earth\u2019s surface but common in meteorites. <\/p>\n The researchers attributed the anomaly, which they initially identified in Italy, Denmark and New Zealand, to the impact of a large asteroid. They argued the unusual layer represented the exact moment in time when dinosaurs disappeared. <\/p>\n First met with skepticism, the iridium anomaly eventually was spotted in more and more places around the world. A decade later, a different group of researchers identified the smoking gun: a 200-kilometer-wide (125-mile-wide) crater off the coast of Mexico\u2019s Yucatan Peninsula. <\/p>\n The rock and sediment there had a similar composition to the iridium layers, and the scientists suggested the depression, called the Chicxulub crater, was caused by the impact of an asteroid. Researchers believe the other anomalies spotted across the globe were caused by scattering debris when the space rock struck Earth. <\/p>\n Most paleontologists now accept that the asteroid caused what\u2019s known as the end-Cretaceous extinction. The strike triggered a period of global cooling, with dust, soot and sulfur thrown up during the impact blocking the sun and likely shutting down photosynthesis, a key process for life. <\/p>\n One fossil site in North Dakota has provided an unprecedented level of detail on what that day \u2014 and its immediate aftermath \u2014 was like. Debris rained down, lodging itself into the gills of fish, while huge tsunami-like surges of water unleashed by the strike killed dinosaurs and other creatures. Scientists have even figured out that the asteroid smashed into Earth in springtime. <\/p>\n The disappearance of massive dinosaurs created a world in which mammals \u2014 and ultimately humans \u2014 were able to thrive. And dinosaurs weren\u2019t the total losers they are sometimes made out to be: Scientists now believe that the birds that flap around in our backyards directly evolved from smaller relatives of Tyrannosaurus rex. <\/p>\n In the wake of the Alvarez duo\u2019s stunning discovery, it initially seemed to scientists as if <\/strong>a space rock impact might be a general mechanism that explained all mass <\/strong>extinction events identified in the geological record. But the end-Cretaceous extinction is the only one reliably associated with an asteroid, according to Benton. <\/p>\n A different culprit, however, does explain several smaller extinction episodes and at least two mass extinctions, including the largest on record. <\/p>\n Something known as a hyperthermal event \u2014 a sudden warming of the planet \u2014 spelled doom for large segments of life on Earth on more than one occasion. These events have followed a predictable pattern: volcanic eruption, carbon dioxide release, global warming, acid rain, ocean acidification \u2014 resulting in a longer road to oblivion than the dino-killing asteroid but equally destructive. <\/p>\n The biggest mass cataclysm of all time, called the end-Permian extinction, occurred 252 million years ago. Some 95% of species disappeared on land and at sea as a result of global warming \u2014 with temperatures rising perhaps 10 degrees Celsius to 15 degrees Celsius (18 F to 27 F), Benton noted in his book. <\/p>\n Known as \u201cthe Great Dying,\u201d the extinction event was marked by supervolcanic eruptions that expelled greenhouse gases in an Australia-size region known as the Siberian Traps in Eurasia. That led to extreme acid rain that killed plant life and left the land surface rocky as the precipitation washed rich soil into the oceans, which in turn became swamped with organic matter, Benton explained. <\/p>\n However, into the void that followed emerged different creatures that evolved from the survivors, displaying many new ways of existence with features such as feathers, hair and speedy locomotion, Benton said. <\/p>\n \u201cOne of the big changes \u2026 on land, it seems, was a great rise in energy of everything,\u201d he explained. \u201cAll of the surviving reptiles very rapidly became upright in posture instead of (low and) sprawling. (Some animals) became warm blooded in some way because we track feathers back to the early Triassic dinosaurs and their nearest relatives, and on the mammals side, we track the origin of hair.\u201d <\/p>\n Another period of extreme volcanic activity 201 million years ago marked the end-Triassic mass extinction. It has been linked to the breakup of the Pangea supercontinent and the opening of the central Atlantic Ocean. Many land reptiles vanished as a result of that catastrophic event, making way for the towering sauropods\u00a0and armored plant eaters\u00a0commonly seen in childhood dinosaur books. <\/p>\n \u201cThe dinosaurs were already around but they had not fully diversified,\u201d Benton said. \u201cAnd then in the early Jurassic, \u2026 the dinosaurs really took off.\u201d <\/p>\n Deeper in time, a mass extinction event\u00a0that ended the Devonian Period, a geological era when life thrived on land for the first time, was also attributed to a hyperthermal event <\/strong>likely triggered by volcanic activity 359 million years ago, according to Benton\u2019s book. <\/p>\n \ufeff<\/strong>Other research published in 2020 suggested that multiple star explosions \u2014 known as supernovae \u2014\u00a0may have played a role. <\/p>\n A less well-understood period of worldwide cooling soon followed. It\u2019s thought that these twin crises \u2014 separated by only 14 million years \u2014 led to rapid changes in temperature and sea level that resulted in the loss of at least 50% of the world\u2019s species, wiping out many armored fish, early land plants, and animals such as the fishapods, or the earliest elpistostegalians, that were making the transition from water to land. <\/p>\n The resulting loss of marine species made way for the golden age of sharks <\/strong>during the Carboniferous Period, when the predators dominated the seas and evolved to include a variety of species with different forms. <\/p>\n Colder temperatures and a drastic drop in sea levels \u2014 perhaps as much as 10 degrees Celsius (18 F) cooler and 150 meters (492 feet) lower, respectively \u2014 played a major role in the earliest identified mass extinction event, the end-Ordovician, according to Benton. That shift, which took place about 444 million years ago, led to the disappearance of 80% of species at a time when life was mostly limited to the seas. <\/p>\n What triggered the die-off was the massive Gondwana supercontinent (today\u2019s South America, Africa, Antarctica and Australia) drifting over the South Pole during the Ordovician. When a land mass covers the polar region, the ice cap reflects sunlight and slows melting, resulting in an expanding ice cap that lowers sea levels globally. <\/p>\n Adding to the cataclysm was volcanic activity. However, in this case, it did not appear to make global temperatures warmer. Instead, phosphorus from lava and volcanic rocks washed into the sea, gobbling up life-giving oxygen from the oceans. <\/p>\n A growing number of scientists believe a sixth mass extinction event of a magnitude equal to the prior five has been unfolding for the past 10,000 years as humans have made their mark around the globe. <\/p>\n The dodo, the Tasmanian tiger,\u00a0the baiji, or Yangtze River dolphin, and the Western black rhino are just a few of the species that have disappeared so far in what\u2019s known as the Holocene or Anthropocene extinction. <\/p>\n While the loss of even one species is devastating, Ceballos of the National Autonomous University of Mexico has highlighted that the ongoing episode of extinction is mutilating much thicker branches of the tree of life, a metaphor and model that groups living entities and maps their evolutionary relationships. <\/p>\n Entire categories of related species, or genera, are disappearing, a process he said is affecting whole ecosystems and endangering the survival of our own species. <\/p>\n Ceballos and his study coauthor Paul Ehrlich, Bing Professor Emeritus of Population Studies at Stanford University, assessed 5,400 genera of vertebrate animals, excluding fishes. A single genus groups one or more different but related species \u2014 for example the genus Canis includes wolves, dogs, coyotes and jackals. <\/p>\n The duo\u2019s analysis found that 73 genera had gone extinct in the past 500 years. This is much faster than the expected \u201cbackground\u201d extinction rate, or the rate at which species would naturally die off without outside influence \u2014 in the absence of human beings, these 73 genera would have taken 18,000 years to vanish, the researchers said. <\/p>\n The causes of these extinctions are varied \u2014 land-use change, habitat loss, deforestation, intensive farming and agriculture, invasive species, overhunting and the climate crisis \u2014 but all these devastating changes have a common thread: humanity. <\/p>\n Ceballos pointed to the extinction of the passenger pigeon, which was the only species in its genus, as an example of how losing a genus can have a cascading effect on a wider ecosystem. The bird\u2019s loss, a result of reckless hunting in the 19th century, narrowed human diets in eastern North America and allowed the bacteria-harboring White-footed mice that were among its prey to thrive. <\/p>\n What\u2019s more, some scientists believe the passenger pigeon\u2019s extinction, combined with other factors, is behind today\u2019s rise of tick-borne diseases such as Lyme disease\u00a0that plague humans and animals alike, according to the study. <\/p>\n Not only do the destructive actions of humans have the potential to erode our quality of life in the long term, but their ripple effects could eventually upend our success as a species, according to Ceballos.<\/strong> <\/p>\n \u201cWhen we lose genera, we\u2019re losing more genetic diversity, we\u2019re losing more evolutionary history, and we\u2019re losing (many) more ecosystem goods and services that are very important,\u201d he explained. <\/p>\n While branches of the tree of life are vanishing, the distribution of certain animal species is becoming more homogenized \u2014 <\/strong>the world is home to about 19.6 billion chickens, 980 million pigs\u00a0and 1.4 billion cattle.\u00a0In some cases, intensive farming can trigger outbreaks of disease like avian influenza outbreaks that rip through poultry farms and increase risk of spillover in wild migratory birds. Other farm animals act as hosts for virus that infect humans, with the potential to cause pandemics like Covid-19. <\/p>\n Ultimately, the planet can and will survive just fine without us, Ceballos added. But, like the iridium anomaly left by the dinosaur-dooming space rock, what might the final traces of human civilization look like in the geological record? <\/p>\n Some scientists point to the geochemical traces of nuclear bomb tests, specifically plutonium \u2014 a radioactive element widely detected across the world in coral reefs, ice cores and peat bogs. <\/p>\n Others say it could be something altogether more mundane, such as a fossilized layer of bones from chickens \u2014 the domesticated bird industrially bred and consumed across the world in mammoth quantities \u2014 that\u2019s left as humanity\u2019s defining legacy for the ages. <\/p>\n\n No species lasts forever \u2014 extinction is part of the evolution of life. But at least five times, a biological catastrophe has engulfed the planet, killing off the vast majority of species from water and land over a relatively short geological interval. The most famous of these mass extinction events \u2014 when an asteroid slammed <\/p>\n","protected":false},"author":0,"featured_media":13227,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[23],"tags":[],"class_list":{"0":"post-13226","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-world"},"_links":{"self":[{"href":"https:\/\/shareperformanceinsight.com\/index.php\/wp-json\/wp\/v2\/posts\/13226","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/shareperformanceinsight.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/shareperformanceinsight.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"replies":[{"embeddable":true,"href":"https:\/\/shareperformanceinsight.com\/index.php\/wp-json\/wp\/v2\/comments?post=13226"}],"version-history":[{"count":0,"href":"https:\/\/shareperformanceinsight.com\/index.php\/wp-json\/wp\/v2\/posts\/13226\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/shareperformanceinsight.com\/index.php\/wp-json\/wp\/v2\/media\/13227"}],"wp:attachment":[{"href":"https:\/\/shareperformanceinsight.com\/index.php\/wp-json\/wp\/v2\/media?parent=13226"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/shareperformanceinsight.com\/index.php\/wp-json\/wp\/v2\/categories?post=13226"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/shareperformanceinsight.com\/index.php\/wp-json\/wp\/v2\/tags?post=13226"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}} A really bad day: Dino-killing asteroid and the iridium anomaly<\/h3>\n
Apocalyptic volcanoes that caused global warming<\/h3>\n
When dinosaurs got big<\/h3>\n
Sinking temperatures and sea levels<\/h3>\n
The looming sixth mass extinction<\/h3>\n