Global fire at the Cretaceous–Tertiary boundary

Wolbach, Wendy S.; Gilmour, I.; Anders, E.; Orth, C. J.; Brooks, R. R.

doi:10.1038/335744e0

Cited by 6 publications

(11 citation statements)

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“…[15] It has been suggested that global firestorms would initiate convection and rainfall that would wash smoke and soot out of the atmosphere and inhibit global distribution of that soot that is observed in the K-Pg boundary sediments in Europe and New Zealand [Wolbach et al, 1985[Wolbach et al, , 1988. Toon et al [2007Toon et al [ , p. 1994 and Turco et al [1990] argued that in major fires the soot production is so great that it will overseed the resulting cumulus clouds, thereby severely inhibiting rainfall.…”

Section: Charcoal Evidencementioning

confidence: 99%

“…[3] Evidence supporting global fires includes the results of physical modeling of the upper atmosphere obtained by Melosh et al [1990], Goldin and Melosh [2009], and others; the presence of reentrant ejecta as a global layer of spherules near the iridium-containing layer [Smit, 1999]; soot in the iridium anomaly layer [Wolbach et al, 1988]; a "fern spike" of spores with an absence of Cretaceous pollen types in sediments above the K-Pg boundary Tschudy et al, 1984;Tschudy and Tschudy, 1986;Vajda et al, 2001]; and a fungal spore spike in the same sediments [Vajda and McLoughlin, 2004]. These data imply the complete destruction of global terrestrial communities within days to months after the impact [Schulte et al, 2010[Schulte et al, , p. 1218, to which Robertson et al [2004a] added evidence from the observed terrestrial survival patterns: No non-aquatic vertebrate much larger than a squirrel survived.…”

Section: Introductionmentioning

confidence: 99%

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K‐Pg extinction: Reevaluation of the heat‐fire hypothesis

et al. 2013

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[1] The global debris layer created by the end-Cretaceous impact at Chicxulub contained enough soot to indicate that the entire terrestrial biosphere had burned. Preliminary modeling showed that the reentry of ejecta would have caused a global infrared (IR) pulse sufficient to ignite global fires within a few hours of the Chicxulub impact. This heat pulse and subsequent fires explain the terrestrial survival patterns in the earliest Paleocene, because all the surviving species were plausibly able to take shelter from heat and fire underground or in water. However, new models of the global IR heat pulse as well as the absence of charcoal and the presence of noncharred organic matter have been said to be inconsistent with the idea of global fires that could have caused the extinctions. It was suggested that the soot in the debris layer originated from the impact site itself because the morphology of the soot, the chain length of polycyclic aromatic hydrocarbons, and the presence of carbon cenospheres were said to be inconsistent with burning the terrestrial biosphere. These assertions either are incorrect or have alternate explanations that are consistent with global firestorms. We show that the apparent charcoal depletion in the Cretaceous-Paleogene layer has been misinterpreted due to the failure to correct properly for sediment deposition rates. We also show that the mass of soot potentially released from the impact site is far too low to supply the observed soot. However, global firestorms are consistent with both data and physical modeling.

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Section: Charcoal Evidencementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

K‐Pg extinction: Reevaluation of the heat‐fire hypothesis

et al. 2013

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“…[5] The hypothesis that major wildfires were a consequence of the K-Pg impact came from the discovery of large amounts of soot in boundary clays [Wolbach et al, 1985[Wolbach et al, , 1988. Measurements at 11 sites around the globe, including North America, Europe, Turkmenistan, and New Zealand, were used to calculate mean values of 11 ± 3 and 2.2 ± 0.7 mg cm À2 for elemental carbon and soot, respectively .…”

Section: Observational Data Used To Support the Wildfire Hypothesismentioning

confidence: 99%

“…[2] The anomalous deposits found at the K-Pg boundary worldwide and long since altered to clays have been linked to a large meteorite impact that formed the Chicxulub structure in the Yucatán, Mexico, and triggered the end-Cretaceous mass extinctions [Alvarez et al, 1980;Schulte et al, 2010]. The discovery of large amounts of soot in K-Pg boundary clays suggested that global wildfires were one of the environmental consequences of this catastrophic impact [Wolbach et al, 1985[Wolbach et al, , 1988. Further support for this hypothesis came from the observed negative shift in δ 13 C in marine K-Pg boundary sites [Ivany and Salawitch, 1993] and the PAH (polycyclic aromatic hydrocarbon) record at distal K-Pg sites [Venkatesan and Dahl, 1989;Arinobu et al, 1999].…”

Section: Introductionmentioning

confidence: 99%

Revisiting wildfires at the K‐Pg boundary

2013

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[1] The discovery of large amounts of soot in clays deposited at the Cretaceous-Paleogene (K-Pg) boundary and linked to the~65 Ma Chicxulub impact crater led to the hypothesis that major wildfires were a consequence of the asteroid impact. Subsequently, several lines of evidence, including the lack of charcoal in North American sites, were used to argue against global wildfires. Close to the impact site fires are likely to be directly ignited by the impact fireball, whereas globally they could be ignited by radiation from the reentry of hypervelocity ejecta. To-date, models of the latter have yet to take into account that ejection -and thus the emission of thermal radiation-is asymmetric and dependent on impact angle. Here, we model: (1) the impact and ejection of material, (2) the ballistic continuation of ejecta around a spherical Earth, and (3) the thermal pulse delivered to the Earth's surface when ejecta reenters the atmosphere. We find that thermal pulses in the downrange direction are sufficient to ignite flora several thousand kilometers from Chicxulub, whereas pulses at most sites in the uprange direction are too low to ignite even the most susceptible plant matter. Our analyses and models suggest some fires were ignited by the impact fireball and ejecta reentry, but that the nonuniform distribution of thermal radiation across the surface of the Earth is inconsistent with the ignition of fires globally as a direct and immediate result of the Chicxulub impact. Instead, we propose that the desiccation of flora by ejecta reentry, as well as the effects of postimpact global cooling/darkness, left much of the terrestrial flora prone to fires, and that the volume of soot in the global K-Pg layer is explained by a combination of syn-and postimpact wildfires.

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“…This study targets the atmosphere after sufficient cooling has taken place. The deposition of energy is also expected to generate fires, which produces large amounts of soot [e.g., Wolbach et al, 1988]. Soot absorbs radiation in the UV region and leads to a reduction in the downward flux at the surface and the absorption of UV radiation in the stratosphere.…”

Section: Atmospheric Models After An Asteroid Impactmentioning

confidence: 99%

Effects of a large asteroid impact on ultra‐violet radiation in the atmosphere

Ishida

Kaiho

Asano

2007

Geophysical Research Letters

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The effects of sulfate aerosols produced as a result of an asteroid impact on the ultra‐violet (UV) radiation are investigated by radiative transfer calculations. After an impact, a reduction in the solar incident radiation and ozone depletion are expected to occur, each of which, in turn, are counteract their on effects on the UV radiation. We estimate reasonable ranges for the amounts of sulfate aerosols and ozone depletion after an impact, and calculate the UV radiation at the Earth's surface, besides absorption in the stratosphere, by changing the aerosol and ozone concentrations within the ranges. The calculation results reveal that the UV‐B (0.28–0.315 μm) radiation depends on both aerosol and ozone concentrations. The reflection of UV‐B radiation by sulfate aerosols cancels out the increase in surface UV‐B radiation due to ozone depletion. This study suggests that, immediately after the Chicxulub impact event, the UV‐B radiation at the Earth's surface would not increase as compared to the pre‐impact levels, since large amount of sulfate aerosols would exist in the stratosphere. Several years after the impact, the UV‐B radiation would increase, because most of the sulfate aerosols would be removed from the atmosphere but their amount would still be enough to destroy ozone and keep it below the harmful level for terrestrial life. In case of the Chicxulub impact, an increase in the UV‐B radiation would have occurred several years after the impact and might have contributed to the mass extinction at the end of the Cretaceous period.

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Global fire at the Cretaceous–Tertiary boundary

Cited by 6 publications

References 0 publications

K‐Pg extinction: Reevaluation of the heat‐fire hypothesis

K‐Pg extinction: Reevaluation of the heat‐fire hypothesis

Revisiting wildfires at the K‐Pg boundary

Effects of a large asteroid impact on ultra‐violet radiation in the atmosphere

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