Inclusive fitness

From Wikipedia, the free encyclopedia

In evolutionary biology, inclusive fitness is one of two metrics of evolutionary success as defined by W. D. Hamilton in 1964:

• Personal fitness is the number of offspring that an individual begets (regardless of who rescues/rears/supports them)
• Inclusive fitness is the number of offspring equivalents that an individual rears, rescues or otherwise supports through its behaviour (regardless of who begets them)

An individual's own child, who carries one half of the individual's genes, is defined as one offspring equivalent. A sibling's child, who will carry one-quarter of the individual's genes, is 1/2 offspring equivalent. Similarly, a cousin's child, who has 1/16 of the individual's genes, is 1/8 offspring equivalent.

From the gene's point of view, evolutionary success ultimately depends on leaving behind the maximum number of copies of itself in the population. Prior to Hamilton's work, it was generally assumed that genes only achieved this through the number of viable offspring produced by the individual organism they occupied. However, this overlooked a wider consideration of a gene's success, most clearly in the case of the social insects where the vast majority of individuals do not produce (their own) offspring.

Overview

Hamilton showed mathematically that, because other members of a population may share one's genes, a gene can also increase its evolutionary success by indirectly promoting the reproduction and survival of other individuals who also carry that gene. This is variously called "kin theory", "kin selection theory" or "inclusive fitness theory". The most obvious category of such individuals is close genetic relatives, and where these are concerned, the application of inclusive fitness theory is often more straightforwardly treated via the narrower kin selection theory. 

Hamilton's theory, alongside reciprocal altruism, is considered one of the two primary mechanisms for the evolution of social behaviors in natural species and a major contribution to the field of sociobiology, which holds that some behaviors can be dictated by genes, and therefore can be passed to future generations and may be selected for as the organism evolves. 

Although described in seemingly anthropomorphic terms, these ideas apply to all living things, and can describe the evolution of innate and learned behaviors over a wide range of species including insects, small mammals or humans.

Belding's ground squirrel provides an example. The ground squirrel gives an alarm call to warn its local group of the presence of a predator. By emitting the alarm, it gives its own location away, putting itself in more danger. In the process, however, the squirrel may protect its relatives within the local group (along with the rest of the group). Therefore, if the effect of the trait influencing the alarm call typically protects the other squirrels in the immediate area, it will lead to the passing on of more copies of the alarm call trait in the next generation than the squirrel could leave by reproducing on its own. In such a case natural selection will increase the trait that influences giving the alarm call, provided that a sufficient fraction of the shared genes include the gene(s) predisposing to the alarm call.

Synalpheus regalis, a eusocial shrimp, also is an example of an organism whose social traits meet the inclusive fitness criterion. The larger defenders protect the young juveniles in the colony from outsiders. By ensuring the young's survival, the genes will continue to be passed on to future generations.

Inclusive fitness is more generalized than strict kin selection, which requires that the shared genes are identical by descent. Inclusive fitness is not limited to cases where "kin" ('close genetic relatives') are involved.

Hamilton's rule

In the context of sociobiology, Hamilton proposed that inclusive fitness offers a mechanism for the evolution of altruism. He claimed that this leads natural selection to favor organisms that behave in ways that correlate with maximizing their inclusive fitness. If a gene (or gene complex) promoting altruistic behavior has copies of itself in others, helping those others survive ensures that the genes will be passed on. 

Hamilton's rule describes mathematically whether or not a gene for altruistic behavior will spread in a population:

${\displaystyle c$

where

• ${\displaystyle r\ }$ is the probability, above the population average, of the individuals sharing an altruistic gene – commonly viewed as "degree of relatedness".
• ${\displaystyle b\ }$ is the reproductive benefit to the recipient of the altruistic behavior, and
• ${\displaystyle c\ }$ is the reproductive cost to the altruist,

Gardner et al. (2007) suggest that Hamilton's rule can be applied to multi-locus models, but that it should be done at the point of interpreting theory, rather than the starting point of enquiry. They suggest that one should "use standard population genetics, game theory, or other methodologies to derive a condition for when the social trait of interest is favored by selection and then use Hamilton's rule as an aid for conceptualizing this result".

Altruism

The concept serves to explain how natural selection can perpetuate altruism. If there is an "altruism gene" (or complex of genes) that influences an organism's behavior to be helpful and protective of relatives and their offspring, this behavior also increases the proportion of the altruism gene in the population, because relatives are likely to share genes with the altruist due to common descent. In formal terms, if such a complex of genes arises, Hamilton's rule (rbc) specifies the selective criteria (in terms of cost, benefit and relatedness) for such a trait to increase in frequency in the population. Hamilton noted that inclusive fitness theory does not by itself predict that a species will necessarily evolve such altruistic behaviors, since an opportunity or context for interaction between individuals is a more primary and necessary requirement in order for any social interaction to occur in the first place. As Hamilton put it, "Altruistic or selfish acts are only possible when a suitable social object is available. In this sense behaviours are conditional from the start." (Hamilton 1987, 420). In other words, whilst inclusive fitness theory specifies a set of necessary criteria for the evolution of altruistic traits, it does not specify a sufficient condition for their evolution in any given species. More primary necessary criteria include the existence of gene complexes for altruistic traits in gene pool, as mentioned above, and especially that "a suitable social object is available", as Hamilton noted. Paul Sherman, who has contributed much research on the ground squirrels mentioned above, gives a fuller discussion of Hamilton's latter point:

To understand any species' pattern of nepotism, two questions about individuals' behavior must be considered: (1) what is reproductively ideal?, and (2) what is socially possible? With his formulation of "inclusive fitness," Hamilton suggested a mathematical way of answering (1). Here I suggest that the answer to (2) depends on demography, particularly its spatial component, dispersal, and its temporal component, mortality. Only when ecological circumstances affecting demography consistently make it socially possible will nepotism be elaborated according to what is reproductively ideal. For example, if dispersing is advantageous and if it usually separates relatives permanently, as in many birds (Nice 1937: 180-187; Gross 1940; Robertson 1969), on the rare occasions when nestmates or other kin live in proximity, they will not preferentially cooperate. Similarly, nepotism will not be elaborated among relatives that have infrequently coexisted in a population's or a species' evolutionary history. If an animal's life history characteristics (Stearns 1976; Warner this volume) usually preclude the existence of certain relatives, that is if kin are usually unavailable, the rare coexistence of such kin will not occasion preferential treatment. For example, if reproductives generally die soon after zygotes are formed, as in many temperate zone insects, the unusual individual that survives to interact with its offspring is not expected to behave parentally. (Sherman 1980, 530, underlining in original)

The occurrence of sibling cannibalism in several species underlines the point that inclusive fitness theory should not be understood to simply predict that genetically related individuals will inevitably recognize and engage in positive social behaviors towards genetic relatives. Only in species that have the appropriate traits in their gene pool, and in which individuals typically interacted with genetic relatives in the natural conditions of their evolutionary history, will social behavior potentially be elaborated, and consideration of the evolutionarily typical demographic composition of grouping contexts of that species is thus a first step in understanding how selection pressures upon inclusive fitness have shaped the forms of its social behavior. Dawkins gives a simplified illustration:

If families [genetic relatives] happen to go around in groups, this fact provides a useful rule of thumb for kin selection: 'care for any individual you often see'." (Dawkins 1979, 187)

Evidence from a variety of species including humans, primates, and other social mammals suggests that contextual cues (such as familiarity) are often significant proximate mechanisms mediating the expression of altruistic behavior, regardless of whether the participants are always in fact genetic relatives or not. This is nevertheless evolutionarily stable since selection pressure acts on the typical conditions, not on the rare occasions where actual genetic relatedness differs from that normally encountered (see Sherman above). Inclusive fitness theory thus does not imply that organisms evolve to direct altruism towards genetic relatives. Many popular treatments do however promote this interpretation, as illustrated in a recent review:

[M]any misunderstandings persist. In many cases, they result from conflating "coefficient of relatedness" and "proportion of shared genes," which is a short step from the intuitively appealing—but incorrect—interpretation that "animals tend to be altruistic toward those with whom they share a lot of genes." These misunderstandings don't just crop up occasionally; they are repeated in many writings, including undergraduate psychology textbooks—most of them in the field of social psychology, within sections describing evolutionary approaches to altruism. (Park 2007, p860)

Such misunderstandings of inclusive fitness' implications for the study of altruism, even amongst professional biologists utilizing the theory, are widespread, prompting prominent theorists to regularly attempt to highlight and clarify the mistakes. Here is one recent example of attempted clarification from West et al. (2010):

In his original papers on inclusive fitness theory, Hamilton pointed out a sufficiently high relatedness to favour altruistic behaviours could accrue in two ways—kin discrimination or limited dispersal (Hamilton, 1964, 1971,1972, 1975). There is a huge theoretical literature on the possible role of limited dispersal reviewed by Platt & Bever (2009) and West et al. (2002a), as well as experimental evolution tests of these models (Diggle et al., 2007; Griffin et al., 2004; Kümmerli et al., 2009 ). However, despite this, it is still sometimes claimed that kin selection requires kin discrimination (Oates & Wilson, 2001; Silk, 2002 ). Furthermore, a large number of authors appear to have implicitly or explicitly assumed that kin discrimination is the only mechanism by which altruistic behaviours can be directed towards relatives... [T]here is a huge industry of papers reinventing limited dispersal as an explanation for cooperation. The mistakes in these areas seem to stem from the incorrect assumption that kin selection or indirect fitness benefits require kin discrimination (misconception 5), despite the fact that Hamilton pointed out the potential role of limited dispersal in his earliest papers on inclusive fitness theory (Hamilton, 1964; Hamilton, 1971; Hamilton, 1972; Hamilton, 1975). (West et al. 2010, p.243 and supplement)

Green-beard effects

As well as interactions in reliable contexts of genetic relatedness, altruists may also have some way to recognize altruistic behavior in unrelated individuals and be inclined to support them. As Dawkins points out in The Selfish Gene (Chapter 6) and The Extended Phenotype, this must be distinguished from the green-beard effect. 

The green-beard effect is the act of a gene (or several closely linked gene), that:

1. Produces a phenotype.
2. Allows recognition of that phenotype in others.
3. Causes the individual to preferentially treat other individuals with the same gene.

The green-beard effect was originally a thought experiment by Hamilton in his publications on inclusive fitness in 1964, although it hadn't yet been observed. As of today, it has been observed in few species. Its rarity is probably due to its susceptibility to 'cheating' whereby individuals can gain the trait that confers the advantage, without the altruistic behavior. This normally would occur via the crossing over of chromosomes which happens frequently, often rendering the green-beard effect a transient state. However, Wang et al. has shown in one of the species where the effect is common (fire ants), recombination cannot occur due to a large genetic transversion, essentially forming a supergene. This, along with homozygote inviability at the green-beard loci allows for the extended maintenance of the green-beard effect.

Equally, cheaters may not be able to invade the green-beard population if the mechanism for preferential treatment and the phenotype are intrinsically linked. In budding yeast (Saccharomyces cerevisiae), the dominant allele FLO1 is responsible for flocculation (self-adherence between cells) which helps protect them against harmful substances such as ethanol. While 'cheater' yeast cells occasionally find their way into the biofilm-like substance that is formed from FLO1 expressing yeast, they cannot invade as the FLO1 expressing yeast will not bind to them in return, and thus the phenotype is intrinsically linked to the preference.

Parental care

In The Selfish Gene, Dawkins reported that some question the idea that parental investment (parental care) contributes to inclusive fitness. The distinctions between the kind of beneficiaries nurtured (collateral versus descendant relatives) and the kind of fitnesses used (inclusive versus personal) in the parsing of nature are independent concepts. This orthogonality can best be understood in a thought experiment: Consider a model of a population of animals such as crocodiles or tangle web spiders. Some species or populations of these spiders and reptiles exhibit parental care, while closely related species or populations lack it. Assume that in these animals a gene, called a, codes for parental care, and its other allele, called A, codes for an absence thereof. The aa homozygotes care for their young, and AA homozygotes don't, and the heterozygotes behave like aa homozygotes if a is dominant, and like AA homozygotes if A is dominant, or exhibit some kind of intermediate behavior if there is partial dominance. Other kinds of animals could be considered in which all individuals exhibit parental care, but variation among them would be in the quantity and quality thereof. 

If one considers a life cycle as extending from conception to conception, and an animal is an offspring of parents with poor parental care, then the higher mortality with poor care could be considered a diminution of the offspring's expected fitness. 

Alternatively, if one considers the life cycle as extending from weaning to weaning, the same mortality would be considered a diminution in the parents' fecundity, and therefore a diminution of the parent's fitness. 

In Hamilton's paradigm, fitnesses calculated according to in the weaning-to-weaning perspective are inclusive fitnesses, and fitnesses calculated in the conception-to-conception perspective are personal fitnesses. This distinction is independent of whether the altruism involved in child rearing is toward descendants or toward collateral relatives, as when aunts and uncle rear their nieces and nephews. 

Inclusive fitness theory was developed in order to better understand collateral altruism, but this does not mean that it is limited to collateral altruism. It applies just as well to parental care. Which perspective one chooses does not affect the animals but just one's understanding.

Parent offspring conflict and optimization

Early writings on inclusive fitness theory (including Hamilton 1964) used K in place of B/C. Thus Hamilton's rule was expressed as is the necessary and sufficient condition for selection for altruism. 

Where B is the gain to the beneficiary, C is the cost to the actor and r is the number of its own offspring equivalents the actor expects in one of the offspring of the beneficiary. r is either called the coefficient of relatedness or coefficient of relationship, depending on how it is computed. The method of computing has changed over time, as has the terminology. It is not clear whether or not changes in the terminology followed changes in computation.

Robert L. Trivers (1974) defined "parent-offspring conflict" as any case where 

${\displaystyle 1$

i.e., K is between 1 and 2. The benefit is greater than the cost, but is less than twice the cost. 

In this case, the parent would wish the offspring to behave as if r is 1 between siblings, although it is actually presumed to be 1/2 or closely approximated by 1/2.

In other words, a parent would wish its offspring to give up ten offspring in order to raise 11 nieces and nephews. The offspring, when not manipulated by the parent, would require at least 21 nieces and nephews to justify the sacrifice of 10 of its own offspring.

The parent is trying to maximize its number of grandchildren, while the offspring is trying to maximize the number of its own offspring equivalents (via offspring and nieces and nephews) it produces. If the parent cannot manipulate the offspring and therefore loses in the conflict, the grandparents with the fewest grandchildren seem to be selected for. In other words, if the parent has no influence on the offspring's behavior, grandparents with fewer grandchildren increase in frequency in the population.

By extension, parents with the fewest offspring will also increase in frequency.

This seems to go against Ronald A. Fisher's "Fundamental Theorem of Natural Selection" which states that the change in fitness over the course of a generation equals the variance in fitness at the beginning of the generation. Variance is defined as the square of a quantity— standard deviation — and as a square must always be positive (or zero). That would imply that e fitness could never decrease as time passes. This goes along with the intuitive idea that you can't select for lower fitness.

During parent-offspring conflict the number of stranger equivalents reared per offspring equivalents reared is going down.

It is considerations of this phenomenon that have caused Orlove (1979) and Grafen (2006) to say that nothing is being maximized.

According to Trivers (1974), if Freud had tried to explain intra-family conflict after Hamilton instead of before him, he would have attributed the motivation for the conflict and for the to resource allocation issues rather than sexual jealousy.

Incidentally, when k=1 or k=2, the average number of offspring per parent stays constant as time goes by. When k<1 k="" or="">2 then the average number of offspring per parent increases as time goes by.

The term "gene" can refer to a locus (location) on an organism's DNA—a section that codes for a particular trait. Alternative versions of the code at that location are called "alleles." If there are two alleles at a locus, one of which codes for altruism and the other for selfishness, an individual who has one of each is said to be a heterozygote at that locus. If the heterozygote uses half of its resources raising its own offspring and the other half helping its siblings raise theirs, that condition is called codominance. If there is codominance the "2" in the above argument is exactly 2.

If by contrast the altruism allele is more dominant, then the 2 in the above would be replaced by a number smaller than 2. If the selfishness allele is the more dominant, something greater than 2 would replace the 2. (Orlove 1975)

Criticism

A 2010 paper by Martin Nowak, Corina Tarnita, and E. O. Wilson suggested that standard natural selection theory is superior to inclusive fitness theory, stating that the interactions between cost and benefit cannot be explained only in terms of relatedness. This, Nowak said, makes Hamilton's rule at worst superfluous and at best ad hoc. Gardner in turn was critical of the paper, describing it as "a really terrible article", and along with other co-authors has written a reply, submitted to Nature.

In work prior to Nowak et al. (2010), various authors derived different versions of a formula for ${\displaystyle r}$, all designed to preserve Hamilton's rule. Orlove noted that if a formula for ${\displaystyle r}$ is defined so as to ensure that Hamilton's rule is preserved, then the approach is by definition ad hoc. However, he published an unrelated derivation of the same formula for ${\displaystyle r}$ – a derivation designed to preserve two statements about the rate of selection – which on its own was similarly ad hoc. Orlove argued that the existence of two unrelated derivations of the formula for ${\displaystyle r}$ reduces or eliminates the ad hoc nature of the formula, and of inclusive fitness theory as well. The derivations were demonstrated to be unrelated by corresponding parts of the two identical formulae for ${\displaystyle r}$ being derived from the genotypes of different individuals. The parts that were derived from the genotypes of different individuals were terms to the right of the minus sign in the covariances in the two versions of the formula for ${\displaystyle r}$. By contrast, the terms left of the minus sign in both derivations come from the same source. One study suggest the c/b ratio be considered as a continuum of this behavioral trait rather than discontinuous in nature. From this approach fitness transactions can be better observed because there is more to what is happening to affect an individual's fitness than just losing and gaining (Engles, W.R. 1982).

Tipping points in the climate system

From Wikipedia, the free encyclopedia

 

Possible tipping elements in the climate system.

 

A tipping point in the climate system is a threshold that, when exceeded, can lead to large changes in the state of the system. Potential tipping points have been identified in the physical climate system, in impacted ecosystems, and sometimes in both. For instance, feedback from the global carbon cycle is a driver for the transition between glacial and interglacial periods, with orbital forcing providing the initial trigger. Earth's geologic temperature record includes many more examples of geologically rapid transitions between different climate states.

Climate tipping points are of particular interest in reference to concerns about climate change in the modern era. Possible tipping point behaviour has been identified for the global mean surface temperature by studying self-reinforcing feedbacks and the past behavior of Earth's climate system. Self-reinforcing feedbacks in the carbon cycle and planetary reflectivity could trigger a cascading set of tipping points that lead the world into a hothouse climate state.

Large-scale components of the Earth system that may pass a tipping point have been referred to as tipping elements. Tipping elements are found in the Greenland and Antarctic ice sheets, possibly causing tens of meters of sea level rise. These tipping points are not always abrupt. For example, at some level of temperature rise the melt of a large part of the Greenland ice sheet and/or West Antarctic Ice Sheet will become inevitable; but the ice sheet itself may persist for many centuries. Some tipping elements, like the collapse of ecosystems, are irreversible.

Definition

The IPCC AR5 defines a tipping point as an irreversible change in the climate system. It states that the precise levels of climate change sufficient to trigger a tipping point remain uncertain, but that the risk associated with crossing multiple tipping points increases with rising temperature. A more broad definition of tipping points is sometimes used as well, which includes abrupt but reversible tipping points.

In mathematics tipping points have been characterised into three types dependent on the underlying mechanisms:

• Bifurcation-induced tipping: System changes abruptly or qualitatively following a slow passage through a bifurcation (eg. Atlantic Meridional Overturning Circulation (AMOC) collapse)
• Noise-induced tipping: Transitions due to random fluctuations/internal variability of the system (eg. Dansgaard-Oeschger events)
• Rate-induced tipping: Failure to track a continuously (slowly) changing steady state (eg. Compost bomb instability)

In the context of climate change, an "adaptation tipping point" has been defined as "the threshold value or specific boundary condition where ecological, technical, economic, spatial or socially acceptable limits are exceeded."

Tipping points for global temperature

There are many positive and negative feedbacks to global temperatures and the carbon cycle that have been identified. The IPCC reports that feedbacks to increased temperatures are net positive for the remainder of this century, with the impact of cloud cover the largest uncertainty. IPCC carbon cycle models show higher ocean uptake of carbon corresponding to higher concentration pathways, but land carbon uptake is uncertain due to the combined effect of climate change and land use changes.

The geologic record of temperature and greenhouse gas concentration allows climate scientists to gather information on climate feedbacks that lead to different climate states, such as the Late Quaternary (past 1.2 million years), the Pliocene period five million years ago and the Cretaceous period, 100 million years ago. Combining this information with the understanding of current climate change resulted in the finding that "A 2 °C warming could activate important tipping elements, raising the temperature further to activate other tipping elements in a domino-like cascade that could take the Earth System to even higher temperatures".

The speed of tipping point feedbacks is a critical concern and the geologic record often fails to provide clarity as to whether past temperature changes have taken only a few decades or many millennia of time. For instance, a tipping point that was once feared to be abrupt and overwhelming is the release of clathrate compounds buried in seabeds and seabed permafrost, but that feedback is now thought to be chronic and long term.

Some individual feedbacks may be strong enough to trigger tipping points on their own. A 2019 study predicts that if greenhouse gases reach three times the current level of atmospheric carbon dioxide that stratocumulus clouds could abruptly disperse, contributing an additional 8 degrees Celsius of warming.

Runaway greenhouse effect

The runaway greenhouse effect is used in astronomical circles to refer to a greenhouse effect that is so extreme that oceans boil away and render a planet uninhabitable, an irreversible climate state that happened on Venus. The IPCC Fifth Assessment Report states that "a 'runaway greenhouse effect'—analogous to Venus—appears to have virtually no chance of being induced by anthropogenic activities." Venus-like conditions on the Earth require a large long-term forcing that is unlikely to occur until the sun brightens by a few tens of percents, which will take a few billion years.

While a runaway greenhouse effect on Earth is virtually impossible, there are indications that Earth could enter a moist greenhouse state that renders large parts of Earth uninhabitable if the climate forcing is large enough to make water vapour (H₂O) a major atmospheric constituent. Conceivable levels of human-made climate forcing would increase water vapour to about 1% of the atmosphere's mass, thus increasing the rate of hydrogen escape to space. If such a forcing were entirely due to CO₂, the weathering process would remove the excess atmospheric CO₂ well before the ocean was significantly depleted.

Tipping elements

Large scale tipping elements

A smooth or abrupt change in temperature can trigger global-scale tipping points. In the cryosphere these include the irreversible melting of Greenland and Antarctic ice sheets. In Greenland, a positive feedback cycle exists between melting and surface elevation. At lower elevations, temperatures are higher, leading to additional melting. This feedback loop can become so strong that irreversible melting occurs. Marine ice sheet instability could trigger a tipping point in West Antarctica. Crossing either of these tipping points leads to accelerated global sea level rise.

When fresh water gets released as a consequence of Greenland melting, a threshold may be crossed which leads to disruption of the thermohaline circulation. The thermohaline circulation transports heat northward which is important for temperature regulation in the Atlantic region. Risks for a complete shutdown are low to moderate under the Paris agreement levels of warming.

Other examples of possible large scale tipping elements are a shift in El Niño–Southern Oscillation. After crossing a tipping point, the warm phase (El Niño) would start to occur more often. Lastly, the southern ocean, which now absorbs a lot of carbon, might switch to a state where it does not do this anymore.

Regional tipping elements

Climate change can trigger regional tipping points as well. Examples are the disappearance of Arctic sea ice, the establishment of woody species in tundra, permafrost loss, the collapse of the monsoon of South Asia and a strengthening of the West African monsoon which would lead to greening of the Sahara and Sahel. Deforestation may trigger a tipping point in rainforests (i.e. Savannization in the Amazon rainforest, ...). As rain forests recycle a large part of their rainfall, when a portion of the forest is destroyed local droughts may threaten the remainder. Finally, boreal forests are considered a tipping element as well. Local warming causes trees to die at a higher rate than before, in proportion to the rise in temperature. As more trees die, the woodland becomes more open, leading to further warming and making forests more susceptible to fire. The tipping point is difficult to predict, but is estimated to be between 3–4 °C of global temperature rise.

Cascading tipping points

Crossing a threshold in one part of the climate system may trigger another tipping element to tip into a new state. These are so-called cascading tipping points. Ice loss in West Antarctica and Greenland will significantly alter ocean circulation. Sustained warming of the northern high latitudes as a result of this process could activate tipping elements in that region, such as permafrost degradation, loss of Arctic sea ice, and Boreal forest dieback. This illustrates that even at relatively low levels of global warming, relatively stable tipping elements may be activated.

Early warning signals

For some of the tipping points described above, it may be possible to detect whether that part of the climate system is getting closer to a tipping point. All parts of the climate system are sometimes disturbed by weather events. After the disruption, the system moves back to its equilibrium. A storm may damage sea ice, which grows back after the storm has passed. If a system is getting closer to tipping, this restoration to its normal state might take increasingly longer, which can be used as a warning sign of tipping.

Changes in the Arctic

A 2019 UNEP study indicates that now at least for the Arctic and the Greenland ice sheet a tipping point has already been reached. Because of dewing of permafrost soil, more methane (in addition to other short-lived climate pollutant) could enter the atmosphere earlier than previously predicted and the loss of reflecting ice shields has started a powerful positive feedback loop leading to ever higher temperatures. The resulting accelerating climate instability in the polar region has potential to affect the global climate, outdating previous predictions about the point in the future when global tipping will occur. 

In June 2019, satellite images from around the Arctic showed burning fires that are farther north and of greater magnitude than at any time in the 16-year satellite record, and some of the fires appear to have ignited peat soils. Peat is an accumulation of partially decayed vegetation and is an efficient carbon sink. Scientists are concerned because the long-lasting peat fires release their stored carbon back to the atmosphere, contributing to further warming. The fires in June 2019, for example, released as much carbon dioxide as Sweden's annual greenhouse gas emissions.

Tipping point effects

If the climate tips into a hothouse Earth scenario, some scientists warn of food and water shortages, hundreds of millions of people being displaced by rising sea levels, unhealthy and unlivable conditions, and coastal storms having larger impacts. Runaway climate change of 4–5 °C can make swathes of the planet around the equator uninhabitable, with sea levels up to 60 metres (197 ft) higher than they are today. Humans cannot survive if the air is too moist and hot, which would happen for the majority of human populations if global temperatures rise by 11–12 °C, as land masses warm faster than the global average. Effects like these have been popularized in books like The Uninhabitable Earth and The End of Nature.

Central Atlantic magmatic province

From Wikipedia, the free encyclopedia

 

The Central Atlantic magmatic province (CAMP) is the Earth's largest continental large igneous province, covering an area of roughly 11 million km². It is composed mainly of basalt that formed before Pangaea broke up in the Mesozoic Era, near the end of the Triassic and the beginning of the Jurassic periods. The subsequent breakup of Pangaea created the Atlantic Ocean, but the massive igneous upwelling provided a legacy of basaltic dikes, sills, and lavas now spread over a vast area around the present central North Atlantic Ocean, including large deposits in northwest Africa, southwest Europe, as well as northeast South and southeast North America (found as continental tholeiitic basalts in subaerial flows and intrusive bodies). The name and CAMP acronym were proposed by Andrea Marzoli (Marzoli et al. 1999) and adopted at a symposium held at the 1999 Spring Meeting of the American Geophysical Union.

The CAMP volcanic eruptions occurred about 201 million years ago and split into four pulses lasting for over ~600,000 years. The resulting large igneous province is, in area covered, the most extensive on earth. The volume of magma flow of ~2–3 × 10⁶ km³ makes it one of the most voluminous as well.

This geologic event is associated with the Triassic–Jurassic extinction event.

Connected magma flows

Location of large residual elements of the Central Atlantic magmatic province

 

Although some connections among these basalts had long been recognized, in 1988 they were linked as constituting a single major flood basalt province (Rampino & Stothers 1988). The basaltic sills of similar age (near 200 Ma, or earliest Jurassic) and composition (intermediate-Ti quartz tholeiite) which occur across the vast Amazon River basin of Brazil were linked to the province in 1999 (Marzoli et al. 1999). Remnants of CAMP have been identified on four continents (Africa, Europe, North America and South America) and consist of thoeliitic basalts formed during the opening of the Atlantic Ocean basin during the breakup of the Pangean supercontinent (Blackburn et al. 2013).

Geographical extent

The province has been described as extending within Pangaea from present-day central Brazil northeastward about 5000 km across western Africa, Iberia, and northwestern France, and from the interior of western Africa westward for 2500 km through eastern and southern North America (McHone 2000). If not the largest province by volume, the CAMP certainly encompasses the greatest area known, roughly 11 million km², of any continental large igneous province. 

Nearly all CAMP rocks are tholeiitic in composition, with widely separated areas where basalt flows are preserved, as well as large groups of diabase (dolerite) sills or sheets, small lopoliths, and dikes throughout the province. Dikes occur in very large individual swarms with particular compositions and orientations. CAMP activity is apparently related to the rifting and breakup of Pangaea during the Late Triassic through Early Jurassic periods, and the enormous province size, varieties of basalt, and brief time span of CAMP magmatism invite speculation about mantle processes that could produce such a magmatic event as well as rift a supercontinent (Wilson 1997), (McHone 2000).

Connection with the Triassic-Jurassic boundary and the associated mass extinction event

In 2013 the CAMP's connection to the end-Triassic extinction, with major extinctions that enabled dinosaur domination of land, became more firmly established. Until 2013, the uncertainties in the geochronologic dates had been too coarse to confirm that the volcanic eruptions were correlated with major climate changes. The work by Blackburn et al. demonstrated a tight synchroneity between the earliest volcanism and extinction of large populations using zircon uranium-lead (U-Pb) dating. They further demonstrated that the magmatic eruptions as well as the accompanying atmospheric changes were split into four pulses lasting for over ~600,000 years (Blackburn et al. 2013).

Before that integration, two hypotheses were in debate. One hypothesis was based especially on studies on Triassic-Jurassic basins from Morocco where CAMP lava flows are outcropping (e.g., Marzoli et al. 2004), whereas the other was based on end-Triassic extinction data from eastern North American basins and lava flows showing an extremely large turnover in fossil pollen, spores (sporomorphs), and vertebrates (Whiteside et al. 2007), respectively.

Morocco

A basaltic lava flow section from the Middle Atlas, Morocco

 

The thickest lava flow sequences of the African CAMP are in Morocco, where there are basaltic lava piles more than 300 metres thick. The most-studied area is Central High Atlas, where the best preserved and most complete basaltic lava piles are exposed. According to geochemical, petrographic and isotopic data four distinct tholeiitic basaltic units were recognized and can be placed throughout the Central High Atlas: Lower, Intermediate, Upper and Recurrent basalts. 

The Lower and Intermediate units are constituted by basaltic andesites, whereas the Upper and Recurrent units have basaltic composition. From Lower to Recurrent unit, we observe:

• a progressive decrease of eruption rate (the Lower and the Intermediate units represent over 80% of preserved lava volume);
• a trend going from intersertal to porphyritic texture;
• a progressive depletion of incompatible element contents in the basalts, possibly linked to a progressive depletion of their mantle source.

Isotopic analyses

Ages were determined by ⁴⁰Ar/³⁹Ar analysis on plagioclase (Knight et al. 2004), (Verati et al. 2007), (Marzoli et al. 2004). These data show indistinguishable ages (199.5±0.5 Ma) from Lower to Upper lava flows, from central to northern Morocco. Therefore, CAMP is an intense, short magmatic event. Basalts of the Recurrent unit are slightly younger (mean age: 197±1 Ma) and represent a late event. Consistently, the Upper and Recurrent basalts are separated by a sedimentary layer that locally reaches a thickness of circa 80 m.

Magnetostratigraphy

According to magnetostratigraphic data, the Moroccan CAMP events were divided into five groups, differing in paleomagnetic orientations (declination and inclination) (Knight et al. 2004). Each group is composed by a smaller number of lava flows (i.e., a lower volume) than the preceding one. These data suggest that they were created by five short magma pulses and eruption events, each one possibly <400 a="" all="" are="" brief="" by="" characterized="" except="" flow="" for="" href="https://en.wikipedia.org/wiki/Paleomagnetism" lava="" long.="" normal="" polarity="" sequences="" title="Paleomagnetism" years="">paleomagnetic

reversal yielded by one lava flow and by a localized interlayered limestone in two distinct section of the High Atlas CAMP.

Palynological analyses

Palynological data from sedimentary layers samples at the base of four lava flow sequences constrain the onset of the CAMP, since there is no evidence of depositional hiatus or tectonic deformation at the bottom of the lava flow piles (Marzoli et al. 2004). The palynological assemblage observed in these basal layers is typical of Late Triassic age, similar to that of the uppermost Triassic sedimentary rocks of eastern North America . Samples from interlayered limestone in lava flows provided unreliable palynological data. One limestone bed from the top to the central High Atlas upper basalts yielded a Late Triassic palynological assemblage. However, the observed sporomorphs in this sample are rare and poorly preserved.

Conclusions

All of these data indicate that the basaltic lava flows of the Central Atlantic magmatic province in Morocco were erupted at c. 200 Ma and spanned the Tr-J boundary. Thus, it is very possible that there is a connection between this magmatic event and the Tr-J boundary climatic and biotic crisis that led to the mass-extinction.

Eastern North America

Basal contact of the North Mountain section of Fundy basin, Nova Scotia, Canada

 

The North American portion of the CAMP lava flows crop out in various sections in the basins of Newark, Culpeper, Hartford, Deerfield, i.e. the Newark Supergroup in New England (USA), and in the Fundy Basin in Nova Scotia (Canada). The CAMP is here constituted by rare olivine- and common quartz-normative basalts showing a great lateral extension and a maximum thickness up to 1 km. The basaltic flows occur on top of continental fluvial and lacustrine sedimentary units of Triassic age. ⁴⁰Ar/³⁹Ar data (on plagioclase) indicate for these basaltic units an absolute age of 198-200 Ma (Hames et al. 2003) bringing this magmatic event undoubtedly close to the Triassic-Jurassic (Tr-J) boundary. Thus it is necessary to determine whether it straddles the boundary or not: if not, then the CAMP could not be a cause of the Late Triassic extinction event. For example, according to Whiteside et al. 2007 there are palynological, geochemical, and magnetostratigraphic evidences that the CAMP postdates the Tr-J boundary.

Magnetostratigraphy

In the Newark basin a magnetic reversal (E23r) is observed just below the oldest basalts and more or less in the same position as a palynologic turnover, interpreted as the Tr-J boundary. In Morocco, two reversal have been detected in two lava flow sequences. Two distinct correlations between the Moroccan and the Newark magnetostratigraphy have been proposed. Marzoli et al. 2004 suggest that the Tr-J boundary is located above the lower reverse polarity level which is positioned more or less at the base of the Intermediate basalt unit of Morocco. These two levels can be correlated with chron E23r of the Newark Basin, therefore the North American CAMP Basalts postdate the Tr–J boundary whereas part of the Moroccan CAMP was erupted within the Triassic. Contrarily, Whiteside et al. 2007 propose that these two levels could be earliest Jurassic intervals of reverse polarity not sampled in the Newark Basin Sequence (many more lava flows are present in the Moroccan Succession than in the Newark Basin), but observed in Early Jurassic sedimentary sequences of the Paris Basin of France. Reverse polarity intervals in America could be present within North Mountain (Fundy basin, Nova Scotia) which are poorly sampled even if previous magnetostratigraphy analysis in this sequence showed only normal polarity, or in the Scots Bay Member of the Fundy basin which have never been sampled. There is only one outcrop in the CAMP of America where reverse polarity is observable: a CAMP–related (about 200 Ma) dike in North Carolina. Whiteside et al. 2007 suggest that reverse polarity intervals in this dike could be of post Triassic age and correlated with the same events in Morocco.

Palynological analyses

The Tr-J boundary is not officially defined, but most workers recognise it in continental strata by the last appearance of index taxa such as Ovalipollis ovalis, Vallasporites ignatii and Patinasporites densus or, in marine sections, by the first appearance of the ammonite Psiloceras planorbis. In the Newark basin the palynological turnover event (hence the Tr-J boundary mass extinction) occurs below the oldest CAMP lava flows. The same can be said for the Fundy, Hartford and Deerfield Basins. In the investigated Moroccan CAMP sections (Central High Atlas Basin), sedimentary layers sampled immediately below the oldest basaltic lava flows, apparently contain Triassic taxa (e.g., P. densus), and were thus defined as Triassic in age as at least the lowest lava flows (Marzoli et al. 2004). Still, a different interpretation is suggested by Whiteside et al. 2007: the sampled sedimentary strata are quite deformed and this can mean that some sedimentary units could be lacking (eroded or structurally omitted). With respect to the Triassic pollens found in some sedimentary units above the Upper Unit basalts, they could have been reworked, so they don’t represent a completely reliable constraint.

Geochemical analyses

CAMP lava flows of North America can be geochemically separated in three units: the older ones are classified as high titanium quartz normative (HTQ) basalts (TiO₂ = 1.0-1.3 wt%); these are followed by lava flows classified as low titanium quartz normative (LTQ) basalts (TiO₂ = ca. 0.8-1.3 wt%); and then by the youngest lava flow unit classified as high titanium iron quartz normative (HTIQ) basalts (TiO₂ = 1.4-1.6 wt%). According to Whiteside et al. 2007, geochemical analyses based upon titanium, magnesium and silicon contents show a certain correlation between the lower North American lava flows and the Lower Unit of the Moroccan CAMP, thus reinforcing the conclusion that the Moroccan basalts postdate the Tr-J boundary. 

Therefore, according to these data, CAMP basalts shouldn’t be included among the direct causes of the Tr-J mass extinction.

Triassic–Jurassic extinction event

From Wikipedia, the free encyclopedia

(H)

K–Pg

Tr–J

P–Tr

Cap

Late D

O–S

Millions of years ago

The blue graph shows the apparent percentage (not the absolute number) of marine animal genera becoming extinct during any given time interval. It does not represent all marine species, just those that are readily fossilized. The labels of the traditional "Big Five" extinction events and the more recently recognised End-Capitanian extinction event are clickable hyperlinks; see Extinction event for more details.

The Triassic–Jurassic extinction event marks the boundary between the Triassic and Jurassic periods, 201.3 million years ago, and is one of the major extinction events of the Phanerozoic eon, profoundly affecting life on land and in the oceans. In the seas, a whole class (conodonts) and 23–34% of marine genera disappeared. On land, all archosaurs other than crocodylomorphs (Sphenosuchia and Crocodyliformes) and Avemetatarsalia (pterosaurs and dinosaurs), some remaining therapsids, and many of the large amphibians became extinct.

Effects

This event vacated terrestrial ecological niches, allowing the dinosaurs to assume the dominant roles in the Jurassic period. This event happened in less than 10,000 years and occurred just before Pangaea started to break apart. In the area of Tübingen (Germany), a Triassic–Jurassic bonebed can be found, which is characteristic for this boundary.

The extinction event marks a floral turnover as well. About 60% of the diverse monosaccate and bisaccate pollen assemblages disappear at the Tr–J boundary, indicating a major extinction of plant genera. Early Jurassic pollen assemblages are dominated by Corollina, a new genus that took advantage of the empty niches left by the extinction.

Statistical analysis of marine losses at this time suggests that the decrease in diversity was caused more by a decrease in speciation than by an increase in extinctions.

Marine vertebrates

Fish did not suffer a mass extinction at the end of the Triassic. The late Triassic in general did experience a gradual drop in actinopterygiian diversity after an evolutionary explosion in the middle Triassic. Though this may have been due to falling sea levels or the Carnian pluvial event, it may instead be a result of sampling bias considering that middle Triassic fish have been more extensively studied than late Triassic fish. Despite the apparent drop in diversity, neopterygiians (which include most modern bony fish) suffered less than more "primitive" actinopterygiians, indicating a biological turnover where modern groups of fish started to supplant earlier groups.

Like fish, marine reptiles experienced a substantial drop in diversity between the middle Triassic and the Jurassic. However, their extinction rate at the Triassic–Jurassic boundary was not elevated. The highest extinction rates experienced by Mesozoic marine reptiles actually occurred at the end of the Ladinian stage, which corresponds to the end of the middle Triassic. The only marine reptile families which went extinct at or slightly before the Triassic–Jurassic boundary were the placochelyids (the last family of placodonts), and giant ichthyosaurs such as shastasaurids and shonisaurids. Nevertheless, some authors have argued that the end of the Triassic acted as a genetic "bottleneck" for ichthyosaurs, which never regained the level of anatomical diversity and disparity which they possessed during the Triassic.

Terrestrial vertebrates

One of the earliest pieces of evidence for a late Triassic extinction was a major turnover in terrestrial tetrapods such as amphibians, reptiles, and synapsids. Edwin H. Colbert drew parallels between the system of extinction and adaptation between the Triassic–Jurassic and Cretaceous-Paleogene boundaries. He recognized how dinosaurs, lepidosaurs (lizards and their relatives), and crocodyliforms (crocodilians and their relatives) filled the niches of more ancient groups of amphibians and reptiles which were extinct by the start of the Jurassic. Olson (1987) estimated that 42% of all terrestrial tetrapods went extinct at the end of the Triassic, based on his studies of faunal changes in the Newark Supergroup of eastern North America. More modern studies have debated whether the turnover in Triassic tetrapods was abrupt at the end of the Triassic, or instead more gradual.

During the Triassic, amphibians were mainly represented by large, crocodile-like members of the order Temnospondyli. Although the earliest lissamphibians (modern amphibians like frogs and salamanders) did appear during the Triassic, they would become more common in the Jurassic while the temnospondyls diminished in diversity past the Triassic–Jurassic boundary. Although the decline of temnospondyls did send shockwaves through freshwater ecosystems, it was probably not as abrupt as some authors have suggested. Brachyopoids, for example, survived until the Cretaceous according to new discoveries in the 1990s. Several temnospondyl groups did go extinct near the end of the Triassic despite earlier abundance, but it is uncertain how close their extinctions were to the end of the Triassic. The last known metoposaurids ("Apachesaurus") were from the Redonda Formation, which may have been early Rhaetian or late Norian. Gerrothorax, the last known plagiosaurid, has been found in rocks which are probably (but not certainly) Rhaetian, while a capitosaur humerus was found in Rhaetian-age deposits in 2018. Therefore, plagiosaurids and capitosaurs were likely victims of an extinction at the very end of the Triassic, while most other temnospondyls were already extinct.

Terrestrial reptile faunas were dominated by archosauromorphs during the Triassic, particularly phytosaurs and members of Pseudosuchia (the reptile lineage which leads to modern crocodilians). In the early Jurassic and onwards, dinosaurs and pterosaurs became the most common land reptiles, while small reptiles were mostly represented by lepidosauromorphs (such as lizards and tuatara relatives). Among pseudosuchians, only small crocodylomorphs did not go extinct by the end of the Triassic, with both dominant herbivorous subgroups (such as aetosaurs) and carnivorous ones (rauisuchids) having died out. Phytosaurs, drepanosaurs, trilophosaurids, tanystropheids, and procolophonids, which were other common reptiles in the late Triassic, had also become extinct by the start of the Jurassic. However, pinpointing the extinction of these different land reptile groups is difficult, as the last period of the Triassic (the Rhaetian) and the first period of the Jurassic (the Hettangian) each have few records of large land animals. Out of the different groups known to have gone extinct in the late Triassic, only phytosaurs, procolophonids, and possibly some basal paracrocodylomorphs are known from fossils considered to be near the Triassic-Jurassic boundary, and other groups may have died out earlier.

Current theories

Several explanations for this event have been suggested, but all have unanswered challenges.

Gradual processes

Gradual climate change, sea-level fluctuations, or a pulse of oceanic acidification during the late Triassic may have reached a tipping point. However, the effect of such processes on Triassic animal and plant groups is not well understood. 

The extinctions at the end of the Triassic were initially attributed to gradually changing environments. Within his 1958 study recognizing biological turnover between the Triassic and Jurassic, Edwin H. Colbert's 1958 proposal was that this extinction was a result of geological processes decreasing the diversity of land biomes. He considered the Triassic period to be an era of the world experiencing a variety of environments, from towering highlands to arid deserts to tropical marshes. On the other hand, the Jurassic period was much more uniform both in climate and elevation due to excursions by shallow seas.

Later studies noted a clear trend towards increased aridification towards the end of the Triassic. Although high-latitude areas like Greenland and Australia actually became wetter, most of the world experienced more drastic changes in climate as indicated by geological evidence. This evidence includes an increase in carbonate and evaporite deposits (which are most abundant in dry climates) and a decrease in coal deposits (which primarily form in humid environments such as coal forests). In addition, the climate may have become much more seasonal, with long droughts interrupted by severe monsoons.

Geological formations in Europe seem to indicate a drop in sea levels in the late Triassic, and then a rise in the early Jurassic. Although falling sea levels have sometimes been considered a culprit for marine extinctions, evidence is inconclusive since many sea level drops in geological history are not correlated with increased extinctions. However, there is still some evidence that marine life was affected by secondary processes related to falling sea levels, such as decreased oxygenation (caused by sluggish circulation), or increased acidification. These processes do not seem to have been worldwide, but they may explain local extinctions in European marine fauna.

Extraterrestrial impact

The Manicouagan reservoir in Quebec, a massive crater formed by a Late Triassic impact. Radiometric dating has determined that it is about 13 million years older than the Triassic–Jurassic boundary, and thus an unlikely candidate for a mass extinction.

 

Some have theorized that an impact from an asteroid or comet may have caused the Triassic–Jurassic extinction, similar to the extraterrestrial object which was the main factor in the Cretaceous–Paleogene extinction about 66 million years ago, as evidenced by the Chicxulub crater in Mexico. However, so far no impact crater of sufficient size has been dated to precisely coincide with the Triassic–Jurassic boundary. 

Nevertheless, the late Triassic did experience several impacts, including the second-largest confirmed impact in the Mesozoic. The Manicouagan Reservoir in Quebec is one of the most visible large impact craters on Earth, and at 100 km (62 mi) in diameter it is tied with the Eocene Popigai crater in Siberia as the fourth-largest impact crater on Earth. Olsen et al. (1987) were the first scientists to link the Manicouagan crater to the Triassic–Jurassic extinction, citing its age which at the time was roughly considered to be late Triassic. More precise radiometric dating by Hodych & Dunning (1992) has shown that the Manicouagan impact occurred about 214 million years ago, about 13 million years before the Triassic–Jurassic boundary. Therefore, it could not have been responsible for an extinction precisely at the Triassic–Jurassic boundary. Nevertheless, the Manicougan impact did have a widespread effect on the planet; a 214-million-year-old ejecta blanket of shocked quartz has been found in rock layers as far away as England and Japan. There is still a possibility that the Manicouagan impact was responsible for a small extinction midway through the late Triassic at the Carnian–Norian boundary, although the disputed age of this boundary (and whether an extinction actually occurred in the first place) makes it difficult to correlate the impact with extinction. Onoue et al. (2016) alternatively proposed that the Manicouagan impact was responsible for a marine extinction in the middle of the Norian which impacted radiolarians, sponges, conodonts, and Triassic ammonoids. Thus, the Manicouagan impact may have been partially responsible for the gradual decline in the latter two groups which culminated in their extinction at the Triassic–Jurassic boundary. The boundary between the Adamanian and Revueltian land vertebrate faunal zones, which involved extinctions and faunal changes in tetrapods and plants, was possibly also caused by the Manicouagan impact, although discrepancies between magnetochronological and isotopic dating lead to some uncertainty.

Other Triassic craters are closer to the Triassic–Jurassic boundary but also much smaller than the Manicouagan reservoir. The eroded Rochechouart crater in France has most recently been dated to 201±2 million years ago, but at 25 km (16 mi) across (possibly up to 50 km (30 mi) across originally), it appears to be too small to have affected the ecosystem. Other putative or confirmed Triassic craters include the 80 km (50 mi) wide Puchezh-Katunki crater in Eastern Russia (though it may be Jurassic in age), the 40 km (25 mi) wide Saint Martin crater in Manitoba, the 15 km (9 mi) wide Obolon' crater in Ukraine, and the 9 km (6 mi) wide Red Wing Creek structure in North Dakota. Spray et al. (1998) noted an interesting phenomenon, that being how the Manicoagan, Rochechoart, and Saint Martin craters all seem to be at the same latitude, and that the Obolon' and Red Wing craters form parallel arcs with the Rochechoart and Saint Martin craters, respectively. Spray and his colleagues hypothesized that the Triassic experienced a "multiple impact event", a large fragmented asteroid or comet which broke up and impacted the earth in several places at the same time. Such an impact has been observed in the present day, when Comet Shoemaker-Levy 9 broke up and hit Jupiter in 1992. However, the "multiple impact event" hypothesis for Triassic impact craters has not been well-supported; Kent (1998) noted that the Manicouagan and Rochechoart craters were formed in eras of different magnetic polarity, and radiometric dating of the individual craters has shown that the impacts occurred millions of years apart.

Volcanic eruptions

Massive volcanic eruptions, specifically the flood basalts of the Central Atlantic Magmatic Province (CAMP), would release carbon dioxide or sulfur dioxide and aerosols, which would cause either intense global warming (from the former) or cooling (from the latter). The record of CAMP degassing shows several distinct pulses of carbon dioxide immediately following each major pulse of magmatism, at least two of which amount to a doubling of atmospheric CO₂.

The isotopic composition of fossil soils of the Late Triassic and Early Jurassic has been tied to a large negative carbon isotope excursion (Whiteside et al. 2010). Carbon isotopes of lipids (n-alkanes) derived from leaf wax and lignin, and total organic carbon from two sections of lake sediments interbedded with the CAMP in eastern North America have shown carbon isotope excursions similar to those found in the mostly marine St. Audrie’s Bay section, Somerset, England; the correlation suggests that the end-Triassic extinction event began at the same time in marine and terrestrial environments, slightly before the oldest basalts in eastern North America but simultaneous with the eruption of the oldest flows in Morocco (Also suggested by Deenen et al., 2010), with both a critical CO
2 greenhouse and a marine biocalcification crisis.

Contemporaneous CAMP eruptions, mass extinction, and the carbon isotopic excursions are shown in the same places, making the case for a volcanic cause of a mass extinction. The catastrophic dissociation of gas hydrates (suggested as one possible cause of the largest mass extinction of all time, the so-called "Great Dying" at the end of the Permian Period) may have exacerbated greenhouse conditions.

Some scientists reject the volcanic eruption theory, because the Newark Supergroup, a section of rock that records the Triassic–Jurassic boundary, contains no ash-fall horizons and the first basalt flows lie around 10 m above the transition zone. However, updated dating protocol and wider sampling has generally confirmed that most (but not all) volcanic activity occurred before the boundary.