Selects: How Extinction Works
Stuff You Should Know examines the concept of extinction, from Earth's past mass extinction events to the possibility of a sixth mass extinction happening now. The hosts explore how various factors, from glaciation to volcanic activity, have caused between 20% to 95% of species to vanish during previous extinction events, and discuss current extinction rates that are hundreds of times higher than the natural background rate.
The hosts delve into the challenges scientists face when studying extinction through fossil records and explain why "de-extinction" technology may not be the answer to species loss. They examine both the "overkill hypothesis" linking extinctions to human expansion and the "climate change hypothesis" connecting them to natural climate shifts made worse by human activity, while considering the practical limitations of bringing extinct species back to life.
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History and Causes of Past Mass Extinctions
Throughout Earth's history, several mass extinction events have dramatically shaped life on our planet. From the Ordovician extinction 490 million years ago to the famous Cretaceous-Paleogene event that ended the dinosaurs' reign, these events eliminated between 20% to over 95% of existing species. Chuck Bryant explains that while each extinction had unique causes—from glaciation to volcanic activity—they all resulted in catastrophic changes to Earth's ecosystems.
Causes of the Potential Sixth Mass Extinction
According to Elizabeth Kolbert, there's growing scientific consensus that Earth is experiencing a sixth mass extinction event. Josh Clark and Chuck Bryant note that current extinction rates are 100 to 1000 times higher than the natural background rate. Two main hypotheses explain this phenomenon: the "overkill hypothesis," which links extinctions to human expansion, and the "climate change hypothesis," which points to natural climate shifts worsened by human activity. Research shows that 177 large mammal species have vanished over the past 132,000 years, coinciding with human population growth.
Challenges In Studying Extinction Due to Fossil Limitations
Josh Clark and Chuck Bryant discuss how the fossil record's limitations complicate our understanding of extinction events. Fossils only form under specific conditions, meaning many extinct species may be completely unrecorded. Bryant explains that "pseudo-extinction"—where species evolve into new forms rather than truly going extinct—further complicates the picture. Researchers must rely on mathematical models to fill these gaps, adding uncertainty to our understanding of historical extinction rates.
Ethical and Practical Considerations of "De-extincting" Species
While technological advances make de-extinction increasingly possible, Bryant and Clark explore the complex ethical and practical challenges involved. They discuss how revived species might lack suitable habitats in the modern world, citing the case of the bucardo—a Spanish mountain goat that survived only minutes after being brought back from extinction. The hosts suggest that conservation efforts should focus on protecting currently endangered species rather than attempting to resurrect extinct ones.
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Clarifications
- The Ordovician extinction, which occurred around 490 million years ago, was one of the major mass extinction events in Earth's history, leading to the loss of a significant percentage of marine species. The Cretaceous-Paleogene event, known for the extinction of the dinosaurs, took place approximately 66 million years ago and had a profound impact on terrestrial and marine life, shaping the course of evolution on Earth.
- The "overkill hypothesis" suggests that human expansion and overhunting have led to the extinction of various species. On the other hand, the "climate change hypothesis" proposes that natural climate shifts, exacerbated by human activities, contribute to the decline of species. These two hypotheses are key explanations for the current high extinction rates and the potential sixth mass extinction event.
- Pseudo-extinction occurs when a species evolves into a new form, leading to the disappearance of the original species while its descendants continue to exist. This concept highlights the transition within an evolutionary lineage, where the ancestral species no longer exists but is succeeded by a new species. Pseudo-extinction can be seen in the example of non-avian dinosaurs evolving into birds, showcasing how the original species is no longer present but has transformed into a new lineage.
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History and Causes of Past Mass Extinctions
The history of Earth is punctuated by several mass extinction events, each with its distinct causes and catastrophic outcomes. These cataclysms have wiped out a significant percentage of species, ranging from 20% to over 95%.
Mass Extinction Events Wiped Out 20% To Over 95% of Species
Ordovician Extinction: Glaciation and Sea Level Changes Eliminate Marine Species
The Ordovician extinction event, occurring about 490 million years ago, eliminated about half of all animal families. Chuck Bryant notes that glaciation during this period lowered sea levels, destroying shallow marine habitats and leading to massive die-offs. Species adapted to certain sea depths, especially shallower ones, either lost their environments or were forced into deeper waters where they faced unfamiliar predators and adverse conditions.
Late Devonian Extinction, ~360 Million Years ago, May Be Linked To Environmental Changes and Marine Ecosystem Disruptions
Taking place roughly 360 million years ago, the Late Devonian extinction saw the disappearance of about a quarter of marine families. Although the specific causes of this extinction remain debated and not entirely clear, environmental changes and disruptions to marine ecosystems are considered significant factors.
Permian-Triassic Extinction: Largest Mass Extinction, Killed 96% of Species 250 Million Years ago, Possibly Due to Volcanic Activity
Also known as the Great Dying, the Permian-Triassic extinction was the most severe mass extinction event recorded, with estimates suggesting that 95 to 96 percent of all species perished. This event, which occurred 250 million years ago, led to the extinction of 85 percent of marine genera and approximately 70 percent of land species. One of the leading hypo ...
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History and Causes of Past Mass Extinctions
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Clarifications
- A nuclear winter-like effect, in the context of the Cretaceous-Paleogene extinction event, suggests that the impact of the asteroid led to the release of particles into the atmosphere. These particles could have blocked sunlight, causing a significant drop in temperatures globally. This cooling effect would have disrupted ecosystems, potentially leading to widespread extinction events.
- The asteroid impact that caused the Cretaceous-Paleogene extinction event is believed to have occurred in what is now the Yucatán Peninsula in Mexico. The impact is estimated to have released energy equivalent to billions of atomic bombs, leading to widespread devastation. The resulting debris and dust thrown i ...
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Causes of the Potential Sixth Mass Extinction
There is a growing consensus in the scientific community that the Earth is experiencing a sixth mass extinction event. Debates on the causes of this cataclysm continue, with human activity at the forefront.
Consensus: Sixth Mass Extinction Underway; Causes Debated
Elizabeth Kolbert, a leading journalist on the topic of extinction, suggests that a consensus exists around the sixth mass extinction being underway. This perspective is echoed in Josh Clark and Chuck Bryant's podcast discussions, where they note that extinction rates are currently estimated to be 100 to a thousand times the natural background rate.
"Overkill Hypothesis": Human Spread Led To Global Megafauna Extinctions
The "overkill hypothesis," hinges on the idea that the spread of human populations led to the extinction of global megafauna. Chuck Bryant references the disappearance of large animals in Australia around 50,000 years ago, coinciding with the expansion of the human footprint. These extinctions included wombat-like creatures the size of hippos and tortoises as big as a VW Beetle.
"Climate Change Hypothesis" Suggests Natural Shifts, Worsened by Human Activity, Are the Main Cause of Current Extinctions
Under the "climate change hypothesis," natural shifts in the climate are considered the main drivers of current extinctions. However, these shifts are believed to be exacerbated by human activities. Josh Clark highlights how even if climate change is a natural shift, human activity bears significance in worsening its impact.
Current human activities, such as farming, logging, road and building construction, and alterations of waterways, contribute significantly to the extinction rate. Moreover, CO2 emissions from human-driven enterprises like chemical plants create ocean acidification. The decrease in ocean pH over the past 50 years could be greater than changes experienced over the previous 50 million years, potentially creating drastic changes in the ocean's chemical composition.
Species Loss Over 132,000 Years Linked To Human Populations
Researchers mapping large animals from 132,000 to 1,0 ...
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Causes of the Potential Sixth Mass Extinction
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Clarifications
- A "sixth mass extinction event" is a term used to describe a period in Earth's history where a significant number of species are rapidly declining or going extinct. This event is characterized by a widespread loss of biodiversity on a global scale. Scientists compare the current rate of species extinction to past mass extinction events, such as the one that wiped out the dinosaurs, to highlight the severity of the current situation. The concept underscores the urgent need to address the factors driving this decline in biodiversity.
- The statement means that the rate at which species are disappearing currently is significantly higher than what would naturally occur without human influence. This rapid loss of species is a cause for concern as it indicates a potential mass extinction event. The comparison to the natural background rate helps emphasize the severity of the situation caused by human activities.
- The "overkill hypothesis" suggests that the spread of human populations led to the extinction of large animals, known as megafauna, due to excessive hunting or other human activities. This theory posits that human actions, such as overhunting, played a significant role in the disappearance of these large species. The term "overkill" in this context implies that humans caused the extinction of megafauna by exerting more pressure than necessary for their survival. This hypothesis highlights the impact of human expansion on ecosystems and the potential consequences for biodiversity.
- Megafauna extinctions refer to the widespread disappearance of large animals, often characterized by significant size compared to most current species. These extinctions can be linked to various factors, including climate change, human activities like hunting and habitat destruction, and natural shifts in ecosystems. The loss of megafauna species can disrupt ecosystems and have cascading effects on other species and the environment. Understanding megafauna extinctions is crucial in studying past biodiversity changes and their implications for current and future ecosystems.
- The "climate change hypothesis" posits that natural climate shifts are the primary drivers of current extinctions. This theory suggests that human activities exacerbate these natural shifts, leading to increased extinction rates. Even if climate change occurs naturally, human actions can worsen its impact on biodiversity. Activities like farming, logging, and industrial emissions contribute to the acceleration of species loss in the current era.
- Ocean acidification is the process where the ocean's pH decreases due to the absorption of carbon dioxide from the atmosphere, leading to increased acidity. This change can harm marine life, especially organisms like corals and mollusks that rely on calcium carbonate to build their shells and skeletons. The decrease in pH is a result of the ocean absorbing carbon dioxide, forming carbonic acid and increasing the concentration of hydrogen ions in the water. Ocean acidification poses a significant threat to marine ecosystems and biodiversity, impacting various species and their habitats.
- The reference to "species loss over 132,000 years" in the text indicates a timeframe over which researchers have o ...
Counterarguments
- The rate of extinction being 100 to a thousand times the natural background rate is based on estimates that may have a wide margin of error due to incomplete fossil records and varying methods of calculation.
- While human activity is a significant cause of biodiversity loss, some argue that factors such as natural climate variability and geological events have also played a role in past mass extinctions and could be contributing factors in the current trends.
- The "overkill hypothesis" is debated, with some researchers suggesting that climate change, disease, and habitat changes could have also played significant roles in the extinction of megafauna.
- The "climate change hypothesis" does not account for all extinctions, as some species may be more resilient to climate change or may even benefit from the changing conditions.
- Human activities are not the sole contributors to extinction rates; invasive species, diseases, and natural disasters also play a role.
- The impact of ocean acidification is still a subject of research, and while it is a concern, the full extent of its effects on marine life and ecosystems is not yet fully understood.
- The link between human population expansion and species l ...
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Challenges In Studying Extinction Due to Fossil Limitations
The study of extinction is faced with complexities that arise from the limitations of the fossil record. Josh Clark and Chuck Bryant delve into the issues that hinder our full comprehension of extinction events through history.
Fossil Record's Incompleteness Hinders Extinction Analysis
Josh Clark begins the conversation by pointing out the early belief that all animals were creations of God and, as such, could not go extinct. This illustrates how historical beliefs and rationalizations have impacted the interpretation of the fossil record.
Fossils Form Under Specific Conditions, Leaving Many Extinct Species Unrepresented
Clark and Bryant explain that, due to the nature of fossil formation, a high number of extinct species might be completely unrepresented in the fossil record. Fossils typically form under specific conditions, such as being encased in amber or covered in ash. As a result, the absence of a fossil does not necessarily equate to a species' extinction. Additionally, Bryant touches on the concept of pseudo-extinction, where a species may have evolved into a new form and stopped appearing in the fossil record, further complicating the understanding of extinction.
Fossil Record's Last Appearance May Not Indicate True Extinction, Risking Underestimates
The point at which a species ceases to appear in the fossil record is an unreliable indicator of its actual extinction event. The discovery of Lazarus species—organisms that reappear in the fossil record after being presumed extinct—highlights the inaccu ...
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Challenges In Studying Extinction Due to Fossil Limitations
Additional Materials
Clarifications
- Pseudo-extinction occurs when a species evolves into a new form, leading to the disappearance of the ancestral species. This concept highlights how a species can transform over time, giving rise to new descendants while the original species no longer exists. An example is the non-avian dinosaurs evolving into birds, showcasing pseudo-extinction where the ancestral form is no longer present but its descendants thrive. Pseudo-extinction can be viewed from both a taxonomic and evolutionary perspective, emphasizing the shift in species classification and the continuous lineage of descendants despite the disappearance of the original species.
- A Lazarus species is a term used in paleontology to describe a taxon that disappears from the fossil record and then reappears later, either as fossils or living organisms. This phenomenon can occur due to factors like incomplete fossil preservation, sampling biases, or the species surviving in specialized or isolated habitats. The term "Lazarus" is derived from the biblical story of Lazarus being raised from the dead, symbolizing the unexpected return of these seemingly extinct species.
- Mathematical models and algorithms in paleontological research are tool ...
Counterarguments
- While historical beliefs may have impacted interpretations of the fossil record, modern paleontology uses rigorous scientific methods that minimize the influence of outdated beliefs.
- Some extinct species may indeed be unrepresented in the fossil record, but the presence of certain fossils can still provide valuable information about past biodiversity and environmental conditions.
- Pseudo-extinction adds complexity to understanding extinction, but it also offers insights into species evolution and adaptation, which can be valuable for evolutionary biology.
- The absence of a fossil does not equate to a species' extinction, but consistent absence across a wide geographic range and through a significant stratigraphic layer can provide strong evidence for extinction.
- The last appearance in the fossil record may not indicate true extinction, but it can still serve as a useful proxy for studying extinction patterns when corroborated with other geological and paleontological evidence.
- Lazarus species do challenge the accuracy of last appearances as proof of extinction, but they also demonstrate the resilience of life and the potential for species to survive in refugia.
- Researchers use models to fill gaps in the fossil record, and while these models introduce uncertainty, they are based on the best available data and statistical methods, and are continually refined as new information becomes available.
- Mathema ...
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Ethical and Practical Considerations of "De-extincting" Species
With advancing technology comes the increasing possibility of reviving extinct species, often known as de-extinction. Such prospects raise ethical questions and practical considerations that both the public and scientific communities grapple with.
Technological Advances Enable Debated De-extinction of Some Species
Podcast hosts Chuck Bryant and Josh Clark express intrigue at the potential for de-extincting species, such as a sloth as big as an elephant, highlighting the curiosity spurred by such technological advances.
De-extinction Raises Ethical Concerns, as Original Habitats May No Longer Exist
However, there are serious concerns about the ramifications of de-extinction, especially the ethical dimension of reviving species when their original habitats may no longer exist. Bryant and Clark discuss the moral complexities of bringing back extinct animals, debating the appropriateness of placing them in zoos given the potential lack of natural environments.
De-extinction Doesn't Ensure Long-Term Survival Due to Adaptation Issues
Bryant discusses the case of the bucardo, a Spanish mountain goat, which was brought back from extinction but only survived a few minutes after birth, emphasizing that de-extinction does not guarantee the long-term survival of a species. This raises points about the adaptation issues that could arise, as animals that have been extinct may not be suited to the current ecosystem or may lack the necessary genetic variety for a sustainable population.
Experts Advise Focusing On Conserving Endangered Species Over De-extinction
Towards the end of their discussion, Bryant and Clark seem to agree that efforts should be directed toward dealing with current extinction rates and conserving endangered species, rather than focusing on de-extinction. Clark s ...
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Ethical and Practical Considerations of "De-extincting" Species
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Counterarguments
- Technological advances in de-extinction could complement conservation efforts by providing a 'back-up' for species at the brink of extinction, offering a potential safety net that could encourage more robust and diverse conservation strategies.
- Ethical concerns regarding de-extinction and habitat loss might be mitigated by creating new, suitable habitats or by using de-extinct species to restore ecosystem functions, which could benefit other species and biodiversity as a whole.
- While de-extinction doesn't guarantee long-term survival, it could be used as a tool for research to better understand extinct species, their biology, and their ecological roles, which could inform conservation strategies for related or similar species.
- Focusing on conserving endangered species is crucial, but de-extinction efforts could also serve as a public engagement tool to raise awareness about extinction and conservation issues, potentially increasing public support and fu ...
Actionables
- You can support conservation by adopting an endangered species through a wildlife charity. By symbolically adopting an animal, you contribute to the protection of its habitat and the species itself. For example, many organizations offer adoption kits that include a certificate and information about the species, and your donation goes towards conservation efforts.
- Enhance your garden or local community space to attract and support native wildlife. Planting native flora can provide food and shelter for local species, helping to maintain biodiversity. You might start with a small butterfly garden or a bird feeder that uses native plants to attract and sustain local bird populations.
- Educate others about the importance of biodiversity and ...
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