The Doomsday Chronicles: Understanding Every Mass Extinction, Including the Imminent Next Cataclysm
Unveiling Earth's catastrophic past: Uncover the mysteries of five devastating mass extinctions and reflect on the impending sixth, as scientists warn of an unfolding ecological crisis
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At least on five separate occasions, a biological disaster has swept across the planet, wiping out the vast majority of species both on land and in the water within a relatively short geological period.
Prionotropis rhodanica Crau
Axel Hochkirch
The latest analysis has revealed the biggest danger to the thousands of species at risk of extinction. The well-known mass extinction event, which occurred 66 million years ago when an asteroid struck Earth, leading to the demise of the dinosaurs and numerous other species, is considered to be the most recent, but experts warn that it will not be the final one.
Researchers argue that we are currently experiencing the sixth mass extinction, not due to a catastrophic asteroid, but because of the destructive actions of one species: Homo sapiens. Human activity such as habitat destruction and the climate crisis have led to this crisis. A study published in the journal PNAS in September revealed that groups of related animal species are disappearing at a rate 35% higher than usual.
The winners and losers of each mass extinction are well-known, but there is no certainty that human beings will be among the survivors in this case. Coauthor Gerardo Ceballos believes that the opposite may occur, with the sixth mass extinction potentially transforming the biosphere into a state where humanity cannot survive without significant action.
"Biodiversity will eventually bounce back, but it is quite challenging to predict the winners. Many of the species that suffered during previous mass extinctions were actually very successful," stated Ceballos, a senior researcher at the Institute of Ecology at the National Autonomous University of Mexico.
Although the reasons behind the "big five" mass extinctions differed, gaining insight into the events and aftermath of these catastrophic events can be enlightening.
"Although no one has witnessed these events, their magnitude suggests the potential for repetition. It is imperative that we learn from historical occurrences since that is our sole source of data," explained Michael Benton, a vertebrate paleontology professor at Bristol University in the United Kingdom and author of the book "Extinctions: How Life Survives, Adapts and Evolves." In his new book, he delves into the topic of "A really bad day: Dino-killing asteroid and the iridium anomaly."
Paleontologists have been studying fossils for centuries, but the field of mass extinction science is relatively new. In the second half of the last century, advancements in radiometric dating and other techniques allowed for a more precise determination of the age of ancient rocks. This set the stage for the work of the late Nobel Prize-winning physicist Luis Alvarez and his geologist son Walter, along with two other colleagues. In 1980, they coauthored a groundbreaking paper on the "iridium anomaly" - a 1-centimeter-thick layer of sedimentary rock rich in iridium, an element rare on Earth's surface but common in meteorites.
Initially discovered in Italy, Denmark, and New Zealand, researchers attributed the anomaly to the impact of a large asteroid, marking the exact moment in time when dinosaurs disappeared. Though met with skepticism, the iridium anomaly was eventually found in more places globally. A decade later, another group of researchers identified the smoking gun: a 200-kilometer-wide (125-mile-wide) crater off the coast of Mexico's Yucatan Peninsula.
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.
Physicist Luis Alvarez and Earth and planetary science professor Walter Alvarez, from the University of California, Berkeley, examine a sample of an iridium layer deposit. From their research in 1980, the father-and-son team hypothesized that a massive asteroid collided with Earth during the Cretaceous Period. [Credit: Roger Ressmeyer/Corbis/VCG/Getty Images]
The end-Cretaceous extinction is widely attributed to the impact of an asteroid, which caused widespread global cooling and blocked the sun due to debris, soot, and sulfur thrown up during the impact. This led to the shutdown of photosynthesis, a critical process for life. A fossil site in North Dakota has provided unprecedented insight into the immediate aftermath of the asteroid strike, revealing debris raining down and leading to the demise of various species. Scientists have also determined that the asteroid collided with Earth during the springtime.
The extinction of huge dinosaurs allowed mammals, and eventually humans, to flourish. Dinosaurs also had their own success, as scientists now believe that birds evolved from smaller relatives of Tyrannosaurus rex. The Alvarez duos discovery initially suggested that asteroid impacts could explain all mass extinctions, but it is now believed that the end-Cretaceous extinction is the only one reliably associated with an asteroid.
A different culprit, however, does explain several smaller extinction episodes and at least two mass extinctions, including the largest on record.
Apocalyptic volcanoes that caused global warming
During several instances in history, a phenomenon known as hyperthermal events, which are characterized by sudden planetary warming, have led to catastrophic consequences for life on Earth. These events typically follow a predictable pattern, beginning with volcanic eruptions, leading to the release of carbon dioxide, global warming, acid rain, and ultimately, ocean acidification. The end result is a prolonged and devastating impact, comparable in destructiveness to the asteroid that wiped out the dinosaurs.
The most significant mass extinction, known as the end-Permian extinction, took place 252 million years ago, resulting in the disappearance of approximately 95% of species on land and in the sea due to the dramatic global warming, which raised temperatures by as much as 10 to 15 degrees Celsius (18 to 27 degrees Fahrenheit), as documented by Benton in his book.
Dubbed "the Great Dying," this extinction event was caused by massive volcanic eruptions in the Siberian Traps region of Eurasia, releasing greenhouse gases and resulting in extreme acid rain. This killed plant life and washed away rich soil, leaving the land barren. The oceans also became overwhelmed with organic matter. As a result, new creatures evolved from the survivors, showcasing features like feathers, hair, and faster movement.
"One of the significant changes ⦠on land, it seems, was a great increase in energy of everything," he explained. "All 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."
Workers are seen loading supplies onto the L/B Myrtle offshore support vessel, which was part of a scientific mission led by the International Ocean Discovery Program in 2016. The mission aimed to study the Chicxulub impact crater located in the Gulf of Mexico, which was formed 66 million years ago after an asteroid hit Earth.
- Ronaldo Schemidt/AFP/Getty Images
During a period of intense volcanic activity 201 million years ago, the end-Triassic mass extinction occurred, which has been associated with the breakup of the Pangea supercontinent and the formation of the central Atlantic Ocean. This catastrophic event led to the disappearance of many land reptiles, creating space for the emergence of towering sauropods and armored plant eaters that are commonly depicted in childhood dinosaur books.
The image depicts the average temperature in degrees Celsius during the warmest month for both Earth and the projected supercontinent (Pangea Ultima) in 250 million years. This environment would pose a significant challenge for the survival of almost all mammal species.
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"Dinosaurs existed but had not yet fully diversified," Benton commented. "It was not until the early Jurassic period that dinosaurs truly flourished."
Further back in time, a mass extinction event marked the end of the Devonian Period, a time when life flourished on land for the first time. This extinction event, likely caused by volcanic activity 359 million years ago, is detailed in Benton's book as a hyperthermal event.
New research from 2020 indicates that the occurrence of multiple supernovae explosions may have had an impact. This was followed by a lesser-known period of global cooling, which is believed to have led to rapid changes in temperature and sea level. As a result, it is estimated that at least half of the world's species were lost, including many armored fish, early land plants, and creatures in the process of transitioning from water to land, such as the fishapods and the earliest elpistostegalians. These twin crises, separated by only 14 million years, are thought to have had a significant impact on the Earth's biodiversity.
The marine species loss led to the rise of the golden age of sharks in the Carboniferous Period, with the predators reigning supreme in the oceans and diversifying into various species with unique forms.
The Siberian Traps, a large region of volcanic activity in Eurasia, caused the largest mass extinction event 252 million years ago. Today, the distant mountains are made up of basalt lava flows, with the Maymecha river visible among the dense volcanic layers. In the foreground, the landscape is covered in rocky debris from the volcanic activity. - Benjamin Black, US Geological Survey
During the end-Ordovician mass extinction 444 million years ago, a dramatic decrease in sea levels and a drop in temperatures by as much as 10 degrees Celsius (18 F) resulted in the extinction of 80% of species that were mostly confined to the seas, according to Benton.
The die-off was caused by the movement of the massive Gondwana supercontinent over the South Pole during the Ordovician era, covering the polar region and expanding the ice cap, which lowered sea levels globally. Additionally, volcanic activity contributed by introducing phosphorus from lava and volcanic rocks into the sea, depleting oxygen levels and impacting marine life.
Scientists are increasingly convinced that a sixth mass extinction event, comparable in scale to the previous five, has been happening over the past 10,000 years as humans have exerted their influence worldwide.
The dodo, Tasmanian tiger, baiji (Yangtze River dolphin), and the Western black rhino are among the species that have gone extinct during the Holocene or Anthropocene extinction. This ongoing episode of extinction is not only devastating, but it is also affecting a wide range of species, as explained by Ceballos of the National Autonomous University of Mexico.
The Monarch butterfly, currently classified as endangered by the International Union for the Conservation of Nature's Red List of Threatened Species, can be seen resting at the Royal Botanical Gardens in Burlington, Ontario, Canada on July 21, 2022.
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Whole ecosystems and the survival of our own species are at risk as entire categories of related species, or genera, are vanishing. According to Ceballos and his study coauthor, Paul Ehrlich, Bing Professor Emeritus of Population Studies at Stanford University, their assessment of 5,400 genera of vertebrate animals (excluding fishes) revealed the alarming impact of this disappearance. For instance, the genus Canis includes wolves, dogs, coyotes, and jackals, demonstrating the scope of this issue.
The analysis of duos revealed that 73 genera have become extinct in the last 500 years, much faster than the expected "background" extinction rate. In the absence of human influence, these 73 genera would have taken 18,000 years to vanish, according to the researchers. The causes of these extinctions are diverse, including land-use change, habitat loss, deforestation, intensive farming and agriculture, invasive species, overhunting, and the climate crisis. However, all these devastating changes share a common thread: humanity.
Specimens of the extinct dodo bird are seen on display in London's Natural History Museum.
Ceballos highlighted the extinction of the passenger pigeon as a case of how the loss of a genus can impact an entire ecosystem. The disappearance of this unique species due to overhunting in the 19th century led to changes in the diet of humans in eastern North America and the subsequent flourishing of White-footed mice, which were a prey of the passenger pigeon and carried harmful bacteria.
Furthermore, according to the study, some scientists contend that the extinction of passenger pigeons, along with other factors, may be contributing to the current increase in tick-borne diseases like Lyme disease, which affects both humans and animals. Ceballos also warns that the detrimental impact of human actions could have far-reaching effects on our quality of life and the long-term success of our species.
"When we lose genera, we are losing a significant amount of genetic diversity, evolutionary history, and essential ecosystem goods and services," he explained.
James' flamingos in the Great Lake Reserve with the pink lake in the background in El Penon, Jujuy, Argentina
Richard McManus/Moment RF/Getty Images
220 flamingos in Argentina have been killed by the latest outbreak of deadly bird flu, leading experts to express concerns about the virus's global spread. As certain animal species face extinction, the distribution of others, such as chickens, pigs, and cattle, is becoming more uniform across the world. Intensive farming can trigger outbreaks of diseases like avian influenza, which can spread to wild migratory birds. Additionally, farm animals can host viruses that can infect humans, potentially leading to pandemics like Covid-19.
The planet can and will ultimately survive without us, said Ceballos. The question remains - what will be the lasting impact of human civilization in the geological record? Some scientists believe that the geochemical traces of nuclear bomb tests, such as plutonium, could be the final remnants of humanity, detected in coral reefs, ice cores, and peat bogs around the world.
Others speculate that it may actually be something ordinary, like a fossilized layer of bones from chickens, the widely bred and consumed domesticated bird, that could ultimately become humanity's defining legacy for future generations.
