ePostcard #153: Extinction Matters
Ask any child to name an extinct animal, and most will tell you the name of their favorite dinosaur. But if you ask them what the word “extinction” means, and if it is forever, their answers are understandably a bit more confused. Extinction is one of the first scientific concepts that kids must grapple with. The meaning of death is a difficult reality for young minds to grasp. Helping children understand the vast span of geologic time and introducing them to ancient worlds through fossils and realistic portrayals in museums and in art is a critical step in that process.
Nash, my 8-year old naturalist friend, having just learned in his 2nd grade class about extinct woolly mammoths, asked me an important question: “If we take better care of Earth will woolly mammoths come back?” His question told me that his teacher is helping him understand the linkage between environmental events on Earth and the extinction of the animals he is learning about. It got us talking about modern elephants, climate change, and a few of the reasons why some very large animals disappeared forever. Our discussions, of course, are ongoing. Before I continue my ePostcard series on South American megafaunal extinctions, I wanted to provide an introduction to the five mass extinction events that Earth has experienced over the vast span of geologic time.
Illustration Credit: Courtesy of the journal, “Cretaceous Research” and paleontologists Steven Jasinski of Harrisburg University (Pennsylvania), Sebastian Dalman and Spencer Lucas of the New Mexico Museum of Natural History and Science, and Nick Longrich of the University of Bath (England). The fossil bones, on which this artist’s rendering of the horned dinosaur is based, were discovered in 2021 in Late Cretaceous rocks of the Hall Lake Formation near Truth or Consequences, New Mexico, on a ranch owned by Ted Turner, founder of the Cable News Network (CNN). The newly discovered horned dinosaur, named Sierraceratops turneri, is believed to have lived in western North America (Laramidia) about 72 million years ago. The horned dinosaurs (Ceratopsidae) were one of the most species-rich groups of herbivorous dinosaurs, and paleontologists believe that further fossil discoveries will enhance our understanding of Cretaceous dinosaur evolution.
THE BIG FIVE MASS EXTINCTIONS
More than 99 percent of all organisms that have ever lived on Earth are extinct. This is how evolution works on our dynamic planet. As new species evolve to fit ever changing ecological niches, older species fade away. The rate of extinction, however, is far from constant. Over the last half billion years, there have been five major extinction events, the so-called “Big Five,” when 75 to more than 90 percent of all species on Earth suddenly disappeared in a geological blink of an eye in losses in global biodiversity that we call mass extinctions. Sadly, most scientists now believe that we are in the Sixth Extinction (also called the Anthropocene Extinction), which some predict will be more devastating than the asteroid impact in the Late Cretaceous that wiped out the dinosaurs.
As we look back through Earth’s history, the fossil record and other key pieces of evidence that geoscientists use to identify the causal factors for global scale mass extinctions all point to profound environmental changes and ecosystem degradation. It is important to remember that Earth isn’t a passive platform on which dynamic populations evolve; our planet is just as dynamic as the populations (animals and plants) it supports, with environments and ecosystems continually changing on scales that range from local and transient to long-term global transformations where the ecological impacts are profound. Population genetics clearly drives the origin of species, but the persistence of species is determined by their ability to adapt and survive Earth’s environmental dynamism. When we study the multiple causal agents in mass extinctions, the only commonality in each case is that environmental disruption was rapid; the rate of environmental change was as important as its magnitude.
Mass extinctions have clearly played a major role in shaping the evolutionary history of life on Earth. The fossil record has shown us that rebuilding biodiversity after mass extinctions can take millions of years. For example, our modern world is mammal-rich largely because non-avian dinosaurs became extinct after the end-Cretaceous mass extinction, which set the stage for global ecosystem change and mammalian diversification. There will always be exceptions, but when environmental change is slow, populations can more easily adapt to their altered living conditions. Most mass extinctions reflect transient but profound environmental disruption, driven by mechanisms operating deep within the Earth, such as catastrophic volcanic eruptions, or by cosmic events (meteorites). Only the end-Cretaceous mass extinctions are reliably linked with a colossal meteorite impact.
THE ROLE OF GLOBAL WARMING IN EXTINCTION
Among the many lessons emerging from the geologic record of mass extinctions, perhaps the most sobering is that humans are now the “geologic force” transforming the global ecological landscape—the Earth’s biological and geochemical systems we depend on for own survival. We humans have unmistakably influenced the planet in profound ways. In describing the role of human-caused global warming in setting the stage for the Sixth Extinction, I am reminded of a favorite quote from ecologist Paul Ehrlich: “In pushing other species to extinction, humanity is busy sawing off the limb on which it perches.”
Greenhouse gases such as CO2 (carbon dioxide), CH4 (methane), and N2O (nitrous oxide), the by-products primarily of fossil fuel combustion and deforestation, have altered the chemical composition of our atmosphere. The concentration of carbon dioxide in the air has risen to more than 40% over the last two centuries, while the concentration of methane, an even more potent greenhouse gas, has more than doubled. In high concentrations, we know that CO2 poses significant challenges for many organisms, impacting their environment and physiology in equal measure. Some species appear relatively tolerant, while others are especially vulnerable.
Anthropogenic climate change is altering the living conditions in the ocean more dramatically today than in the past 50 to 300 million years. The oceans are becoming warmer as they absorb more than 90 percent of the heat trapped in the atmosphere by greenhouse gases; at the same time they absorb large amounts of carbon dioxide, which chemically react with constituents of seawater, making the oceans more acidic. But that’s not all: for various reasons, warming oceans store less oxygen (O2) and can become hypoxic (oxygen-poor), especially at depths beyond direct contact with the atmosphere. In other words, they gradually lose their lifeblood. But organisms need to breathe so that their bodies can produce energy – and the warmer the oceans become, the greater their oxygen requirements become.
At Germany’s Alfred Wegener Institute, Dr. Hans-Otto Pörtner and his colleagues have focused their research on linking biogeography and ecosystem functioning to molecular, biochemical and physiological mechanisms that might shape an organism’s tolerance and performance. For example, the researchers have shown that the ability to supply the body with sufficient oxygen is subject to a certain limit, which varies by species. If this limit is exceeded, the cardiovascular system collapses.
Understanding the biological consequences of 21st century global change—the ‘deadly trio’ of global warming, ocean acidification, and oxygen depletion (hypoxia)—brings a sense of urgency to the research. The scale of biodiversity losses we are now seeing in marine ecosystems are just beginning to resemble the mass extinctions of Earth’s distant past. Figuring out how marine organisms’ energy requirements have changed in the wake of climate change, how large their pH, temperature and oxygen tolerances are, and what behaviors could enable them to adapt to new environmental conditions has become our next challenge.
So far, it appears that the large majority of marine life that are not sessile are fleeing the heat as far as is geographically possible. Around the world, marine species are shifting their habitats polewards or to greater depths. The increasing lack of oxygen in the seas simultaneously reduces the number of safe havens remaining to them. Increasing ocean acidification puts organisms under additional pressure. Further, these three climate impacts are mutually reinforcing.— each factor makes the effects of the others worse. For example, the direct physiological effects of increased CO2 can cause hypercapnia, a condition in which proteins that normally transport O2 through the body can bind instead with CO2, hindering oxygen metabolism.
END-ORDOVICIAN MASS EXTINCTION
end-Ordovician Illustration Credit (above): Courtesy of artist Ntvtiko (Tiko) and the Required Brain (requiredbrain.com).
1. Ordovician-Silurian Mass Extinction (End-Ordovician)
• When: The Ordovician Period of the Paleozoic Era (ending about 445 million years ago)
• Size of the Extinction: Up to 86% of all living species eliminated, including about half of all ocean-dwelling animal genera
• Suspected Cause or Causes: Continental movements resulting from plate tectonics and subsequent climate change, with widespread glaciation causing sea levels to drop by approximately 100 meters.
end-Devonian Illustration Credit (above): Courtesy of artist Ntvtiko (Tiko) and Required Brain.
2. End-Devonian Mass Extinction
• When: The Devonian Period of the Paleozoic Era (biodiversity decline occurring between 393-359 million years ago)
• Size of the Extinction: Nearly 80% of all living species eliminated (sometimes referred to as a “mass depletion”)
• Suspected Cause or Causes: Least well understood of “Big Five” events. Lack of oxygen in the oceans, quick cooling of air temperatures, volcanic eruptions and/or meteor strikes
Permian-Triassic (end-Permian) Illustration Credit (above): Artistic visualization courtesy of Artox1 and Required Brain (requiredbrain.com).
3. End-Permian Mass Extinction
• When: The Permian Period of the Paleozoic Era (about 252 million years ago, at the close of the Permian)
• Size of the Extinction: This is the largest mass extinction (sometimes called “The Great Dying”), with more than 90% of all aquatic and terrestrial species eliminated
• Suspected Cause: Unknown—possibly a combination of asteroid strikes, volcanic activity, climate change, and toxic microbes
The causes of the end-Permian Extinction—the most biologically catastrophic of all five mass extinctions—continue to be debated. The list of causal triggers includes one or more large meteor strikes, massive volcanic eruptions and thousands of years of basaltic lava flows, global warming associated ocean acidification, oxygen depletion, and toxic gas emissions. As you see in the illustration below, there is abundant fossil evidence that a multitude of marine species, including calcareous sponges, corals, Bryozoans (“moss” animals), trilobites, Echinoderms (sea stars and urchins), and Blastoids were all impacted. Vertebrates such as amphibians, reptiles, and mammal-like reptiles were also lost.
End-Permian Extinction Illustration Credit (above): Courtesy of J. Penn / C. Deutsch / E. Haeckel / W. Kaveney / H. Fjeld / J. White. Schematic illustration of temperature-dependent hypoxia (toxic low oxygen levels) in the ocean as one driver of the end-Permian marine mass extinction. Warming decreases the amount of O2 that can be mixed into seawater, which results in hypoxia.
Illustration Credit: These examples of the extinct “Blastoidea” (stalked filter-feeders) are courtesy of Ernst Haeckel’s Art Forms of Nature, 1904.
End-Permian Illustration Credit: Courtesy of Earth Archives and artist Julio Lacerda.
Artist Julio Lacerda’s depiction of the catastrophic outpouring of basaltic lava (the so-called Siberian Traps), which covered around 3 million square miles, are believed to have been one of the largest volcanic events in Earth’s history. Subsequent eruptions might have caused large amounts of carbon dioxide to be released into the atmosphere, possibly culminating in a large-scale global warming effect on land and in the surface layers of the ocean in a short period of time. The eruptions certainly would have caused acid aerosols and dust clouds to be released into the atmosphere, which resulted in sun-blocking cloud cover, reduced photosynthesis, outgassing of toxic sulphur dioxide, widespread acid rain, and global cooling.
End-Triassic Illustration Credit (above): Courtesy of Phys.org, Steve Brusatte, Professor Michael Benton, and colleagues at the University of Bristol (UK). This reconstructed scene is taken from Steve Brusatte´s book Dinosaurs (Quercus Publishing, London). The illustration shows a herd of primitive carnivorous dinosaurs (Coelophysis, foreground) is enveloped by a sandstorm, while a large carnivorous crocodile-like archosaur (Postosuchus) and several early sauropodomorph dinosaurs lurk in the background.
4. End-Triassic Mass Extinction
• When: The end of the Triassic Period of the Mesozoic Era (about 201 million years ago)
• Size of the Extinction: More than 70% of all living species went extinct
• Suspected Cause or Causes: Plate tectonic rifting, major volcanic activity with basalt flooding, global climate change, marine photic zone euxinia (PZE), and changing pH and sea levels of the oceans.
The causes of the end-Triassic extinction remains a matter of debate. Some scientists believe that the rifting of the supercontinent Pangea, where eastern North America met northwestern Africa, may have released up to 100,000 gigatons of carbon dioxide, which likely strengthened the global greenhouse effect, increasing average air temperatures around the globe by as much as 18–27 °F (10–15 °C), and acidifying the oceans.
Modern studies examining the region’s flood basalts generated by this rifting reveal that the rocks were created during a 620,000-year interval of volcanic activity that occurred at the end of the Triassic. The volcanism of the first 40,000 years of this interval was particularly intense and coincided with the beginning of the mass extinction some 201.5 million years ago. Other evidence suggests that relatively modest rising carbon dioxide concentrations in the atmosphere could also have liberated massive amounts of methane trapped in permafrost and undersea ice. Methane, a much more effective greenhouse gas than carbon dioxide, could have caused Earth’s atmosphere to warm significantly.
End-Triassic Illustration Credit (above): Courtesy of Earth Archives (eartharchives.org)
End-Triassic Extinction Illustration Credit (above): Courtesy of Victor Leshyk and sci-news.com/paleontology.
THE ROLE OF TOXIC OCEANS IN THE END-TRIASSIC MASS EXTINCTION
Geoscientists tell us that the end-Triassic world experienced environmental challenges similar to those we are facing on Earth right now. Given our concerns about the impacts of global warming, acidification, and toxic algal blooms on our modern oceans, an article published in the journal Geology (April, 2015) caught my attention. The article provides compelling evidence that the end-Triassic mass extinction some 201 million years might have been caused by changes in the biochemical balance of the Panthalassic Ocean – the larger of the two oceans surrounding the supercontinent of Pangaea. Why is this important?
Many atmospheric scientists believe that the Late Triassic ended in a runaway greenhouse climate that might have transformed Earth’s oceans into warm, stagnant death traps for countless marine species. Sound familiar? Dr. Alex Kasprak and a team of researchers from the United States, United Kingdom, Australia, and Canada, discovered and analyzed fossilized organic molecules extracted from a rock sequence made up of sediments that accumulated on the bottom of the north-eastern Panthalassic Ocean, now exposed in outcrops on British Columbia’s Queen Charlotte Islands/Haida Gwaii. Their results were nothing less than stunning.
The molecules they analyzed were from photosynthesizing brown-pigmented green sulfur bacteria – microorganisms that only exist under severely anoxic (oxygen-depleted) conditions. The analysis provided proof of severe oxygen depletion and hydrogen sulfide poisoning in the uppermost layers of the ocean at the end of Triassic. The ocean is divided into three zones—photic, disphotic, and aphotic—based on depth and in-coming light levels. The photic zone is the layer of the ocean that receives direct sunlight and is sufficiently illuminated to permit photosynthesis by phytoplankton and seaweeds. The thickness of the photic zone varies with the intensity of sunlight as a function of season and latitude and with the degree of water turbidity. For animals in the photic zone, the daily cycle of light and dark is perhaps the most powerful environmental signal available. The uppermost zone of the ocean is critically important because the phytoplankton, the primary producers upon which the rest of the food web depends, are concentrated in these zones. Sunlight insufficient for photosynthesis characterizes the disphotic zone, which extends from the base of the photic zone downward to the aphotic zone, the region of perpetual darkness that includes most of the ocean’s water.
This study also documented marked changes in the nitrogen composition of organic matter, indicating that disruptions in marine nutrient cycles coincided with the development of low oxygen conditions. Keep in mind that the primary, naturally-occurring greenhouse gases in Earth’s atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Euxinic conditions occur when water is both anoxic (oxygen-poor) and sulfidic (hydrogen sulfide-rich). The research clearly links Triassic greenhouse conditions to the toxic build-up of carbon dioxide (CO2)—conclusive evidence of marine photic zone euxinia (PZE) and disrupted biogeochemistry in the coastal shelf waters of the Panthalassic Ocean during the end-Triassic. PZE occurs when the sunlit surface waters of the ocean become devoid of oxygen and are poisoned by hydrogen sulfide – a by-product of microorganisms that live without oxygen and are extremely toxic to most other life forms. But what caused the toxic build-up of CO2? The researchers point to the well-dated, massive outpourings of basalt lava and gaseous clouds erupting from volcanic fissures associated with the Triassic opening of the Atlantic Ocean.
In an interview with Science News, Dr. Jessica Whiteside (University of Bristol, UK), a member of the research team, offered this explanation for how the deadly PZE conditions might have been created: “As tectonic plates shifted to break up Pangaea, huge volcanic rifts would have spewed carbon dioxide into the atmosphere, leading to rising temperatures from the greenhouse effect. The rapid rise in CO2 would have triggered changes in ocean circulation, acidification and deoxygenation. The resulting boom in marine microbes consumed oxygen and released poisonous hydrogen sulfide into the water and air, creating ‘dead zones’ above and below. These changes certainly had the potential to disrupt nutrient cycles and alter food chains essential for the survival of marine ecosystems. Our data now provide direct evidence that anoxic, and ultimately euxinic, conditions severely affected food chains. The same carbon dioxide rise that led to the oxygen depleted oceans also led to a mass extinction on land, and ultimately to the ecological take-over by dinosaurs, although the mechanisms are still under study.”
Research Source: Alex H. Kasprak et al. 2015. Episodic photic zone euxinia in the northeastern Panthalassic Ocean during the end-Triassic extinction. Geology, vol. 43, no. 4, pp. 307-310; doi: 10.1130/G36371.1
THE ROLE OF VOLCANOES IN THE END-TRIASSIC MASS EXTINCTION
People who don’t believe the science behind human-caused climate change often point to volcanoes as the real culprits. Earth stores a huge amount of carbon in rock—far more than in the oceans or the atmosphere. While some of it escapes into the atmosphere from volcanoes, volcanic emissions of CO2 in our modern world—the Anthropocene—are tiny compared to human emissions. Volcanic eruptions in Iceland, Argentina, Hawaii and other global locations appear impressive to our eyes, inundating landscapes with lava flows, destroying property, and producing ash-ladened, toxic clouds that can cause respiratory problems and curtail air travel. Modern day eruptions don’t come close to those that set the stage for the end-Triassic mass extinctions.
About 200 million years ago, at the end of the Triassic period, about three-quarters of all species died out. This mass extinction was very likely triggered by widespread volcanic eruptions, which emitted enormous amounts of carbon dioxide, causing global warming. In searching for the latest studies on volcanoes and CO2 production, I discovered a fascinating article in the online journal Nature Communications (2020) —Deep CO2 in the end-Triassic Central Atlantic Magmatic Province (CAMP)—by Dr. Manfredo Capriolo (University of Padova, Italy) and a stellar international team of geoscientists.
Their research supports and further illuminates the linkage between volcanically produced CO2 and the end-Triassic Mass Extinction. “These mega-volcanic events coincide in time with the mass extinction events,” says Dr. Capriolo, “The eruptions occurred in bursts over hundreds of thousands of years, with each burst lasting about 500 years.” By studying bubbles of gas trapped in ancient volcanic rock, Capriolo and his colleagues determined how much carbon dioxide each burst released, and suggest that a single pulse of volcanic activity could have contributed to dramatic changes to the climate at the end of the Triassic. The amount was similar to the human-caused emissions expected this century.
To fill in the gaps in my understanding of volcanic sources for CO2 emissions, I did a little reading on “Large Igneous Provinces” (abbreviated as LIPs) and how are they created. LIPs are defined as mostly volcanically-erupted or near-surface intrusive emplacements of predominantly iron- and magnesium-rich magma plumes that emanate from deep within Earth’s core–mantle boundary region. Because of what geoscientists have learned about these geologically dramatic and volatile magmatic events, LIPs have become an important research focus in identifying the causal agents in climate change and mass extinctions.
Capriolo and his colleagues analyzed over 200 samples from basaltic lava flows and sills, recognizing a host of chemicals released during eruptions that can wreak havoc on the environment and climate. They include CO, CO2, CH4, SO2, H2S, HCl, and CH3Cl. The researchers were primarily concerned with CO2 and their results showed that the CAMP eruptions produced up to 100,000 gigatons of CO2 and that part of that came from the middle-lower crust and mantle. The origins of that carbon dioxide are important, because it suggests that the eruptions were very rapid and catastrophic. The researchers say that the eruptions were pronounced “pulses” of CO2. Because those pulses were so rapid, they overwhelmed the Earth’s capacity to re-absorb it. The researchers suggest that the amount of CO2 produced in these eruptions is roughly equal to the amount of CO2 released into the atmosphere by humans in the 21st century. Even a single pulse may have done so. Said Capriolo, “We’re managing to release as much CO2 as a single, massive volcanic pulse did hundreds of millions of years ago.
Reference Source: Nat Commun. 2020; 11: 1670 (Published online 2020 Apr 7. doi: 10.1038/s41467-020-15325-6)
THE AGE OF DINOSAURS
Dinosaurs originated about 238 million years ago and survived 2 mass extinctions (the end-Permian and end-Triassic mass extinctions) and 50 million years before taking over the world and dominating terrestrial and marine ecosystems during the Cretaceous Age of Dinosaurs. The rapid expansion of carnivorous and armored dinosaur groups did not happen until after the much bigger mass extinction some 201 million year ago, at the Triassic-Jurassic boundary. At least half of the species now known to have been living on Earth at that time became extinct, which profoundly affected life on land and in the oceans. The extinction of their predecessors that allowed herbivorous dinosaurs to expand into the niches they left behind.
END-CRETACEOUS (or K-Pg) MASS EXTINCTION
End-Cretaceous Extinction Illustration Credit (above): Courtesy of SciTecDaily, Yale University’s Earth News (January 2018), and Yale geophysicist Dr. Pincelli Hull and her colleagues,
5. End-Cretaceous (or K-Pg) Mass Extinction
• When: The end of the Cretaceous Period of the Mesozoic Era (about 66 million years ago)
• Size of the Extinction: About 76% of all living species went extinct, including the majority of non-avian dinosaurs
• Cause: Asteroid impact, with additional carbon dioxide emissions from Deccan Trap volcanism that might have increased the overall greenhouse effect
The end-Cretaceous mass extinction (also known as the Cretaceous–Paleogene or K–Pg) is perhaps the most famous of the Big Five because it caused the sudden extinction of more than 75% of all of the plant and animal species on Earth, including all of the non-avian dinosaurs. With the exception of some cold-blooded (ectothermic) species such as sea turtles and crocodilians, no tetrapods (four-limbed vertebrate animals ) weighing more than 55 pounds are believed to have survived the mass extinction event. It marked the end of the Cretaceous period, and with it the Mesozoic Era, while heralding the beginning of the Cenozoic Era, the Age of Mammals.
But extinction also provided evolutionary opportunities, and many groups underwent remarkable adaptive radiation—a sudden and prolific divergence into new forms and species within the disrupted and emptied ecological niches. Mammals in particular underwent dramatic diversification during the Paleogene, evolving new forms such as horses, whales, bats, and primates. The surviving group of dinosaurs were bird-like animals that would ultimately evolve into the wondrous diversity of bird families we know today.
THE CHICXULUB IMPACT AND THE END OF THE AGE OF DINOSAURS
In the geologic record, the end-Cretaceous event, dated at about 66 million years, is marked by a thin layer of sediment called the K–Pg boundary, which can be found throughout the world in marine and terrestrial rocks. The boundary clay shows unusually high levels of the metal iridium, which is more common in asteroids than in the Earth’s crust. May years ago I was fortunate to have Dr. Martin Lockley, a paleontologist who is the world’s expert on dinosaur trackways, take one of my Cloud Ridge groups to see an exposure of the K–Pg boundary layer near Trinidad (Colorado). The layer seemed almost insignificant as it angled across the face of the cliff, but it was impossible not feel the power of that “geologic moment” in time.
Evidence that the end-Cretaceous mass extinction was caused by a meteorite impact, an hypothesis first proposed in 1980 by a team of scientists led by physicist and Nobel laureate Dr. Luis Alvarez and his geologist son Walter, generated fierce debate among scientists but also inspired some of the most fascinating geologic sleuthing of all time. The extinction debate went back and forth between proponents of a meteorite impact and those that favored catastrophic volcanism as the cause. The “Alvarez impact” hypothesis was bolstered in the early 1990s by the discovery of the 112 mile-wide Chicxulub crater in the Gulf of Mexico’s Yucatán Peninsula, which provided conclusive evidence that the iridium-rich K-Pg boundary clay I described above represented debris from a colossal asteroid impact. It was estimated that the expanse of the impact zone would have required a massive comet or asteroid estimated to be 6 to 9 miles in width. The fact that the extinctions occurred simultaneously also provided strong evidence that the extinctions were caused by an asteroid.
In a 2013 paper, Dr. Paul Renne of the Berkeley Geochronology Center dated the impact at 66.043±0.011 million years ago, based on argon–argon dating, and that the mass extinction occurred within 32,000 years of the impact date. In 2018, in the journal Science, Yale University geophysicist Dr. Pincelli Hull and her colleagues established a more definitive timeline for the massive volcanic eruptions in India that produced the Deccan Traps (basalt floods) as having occurred well before the end-Cretaceous mass extinction 66 million years ago, and that the Chicxulub impact could have triggered eruptions at active volcanoes elsewhere on Earth.
A 2016 drilling project into the Chicxulub peak ring confirmed that it consists of granite ejected from much deeper in the Earth by the force of the impact. Further analysis showed that the granite had been ‘shocked’ by the immense pressure of the impact and melted in minutes. Unlike sea-floor deposits, the drill rock core contained hardly any gypsum, the usual sulfate-containing sea floor rock in the region. The researchers suggested that the gypsum would have vaporized and dispersed as an aerosol into the atmosphere, which would also have caused longterm effects on the climate and food chain.
In 2019, another group of researchers provided evidence suggesting that a persistent dust cloud could have blocked sunlight for up to a year, inhibiting photosynthesis by plants and plankton. The asteroid hit an area of carbonate rock containing a large amount of combustible hydrocarbons and sulphur, much of which was vaporized, thereby injecting sulfuric acid aerosols into the stratosphere, which might also have reduced the amount of sunlight reaching the Earth’s surface by more than 50%, and would have caused acid rain. The resulting acidification of the oceans would have exterminated many of the organisms that grow shells of calcium carbonate.
The cataclysmic Chicxulub Impact is now widely accepted as the primary cause of the end-Cretaceous mass extinction. The impact force of an asteroid of that size colliding with the Earth has been estimated to have released the equivalent energy of several million nuclear weapons detonating simultaneously—more than a billion times the energy of the atomic bombings of Hiroshima and Nagasaki.
PHOTOS OF THE K-PG IRIDIUM LAYER
Photo Credits: Courtesy of Wikipedia (en.wikipedia.org). In the photo above you see the badlands near Drumheller, Alberta, where erosion has exposed the K–Pg boundary. The 2nd photo above shows a hand pointing to the Cretaceous–Paleogene clay layer (gray) in the Geulhemmergroeve tunnels near Geulhem, The Netherlands.
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