An impressive amount of evidence supports the proposal of Alvarez et al. that the Cretaceous era was ended abruptly by the impact of a comet or asteroid. The recent discovery of an apparently global soot layer at the Cretaceous/Tertiary boundary indicates that global wildfires were somehow ignited by the impact. Here we show that the thermal radiation produced by the ballistic re-entry of ejecta condensed from the vapour plume of the impact could have increased the global radiation flux by factors of 50 to 150 times the solar input for periods ranging from one to several hours. This great increase in thermal radiation may have been responsible for the ignition of global wildfires, as well as having deleterious effects on unprotected animal life.
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"A significant perturbation of the global carbon cycle has been predicted from extinctions themselves, as well as from impact and volcanic eruption near the K–T boundary. It was hypothesized that atmospheric CO 2 would rise dramatically across the K–T transition due to massive amounts of CO 2 from Chicxulub's target carbonate-rich lithologies and the projectile (O'Keefe and Ahrens, 1989; Agrinier et al., 2001; Kring, 2007), from widespread large wildfires (Melosh et al., 1990; Wolbach et al., 1990; Ivany and Salawitch, 1993; Durda and Kring, 2004), from intruded or impacted coal or hydrocarbons (Belcher et al., 2005; Harvey et al., 2008; Belcher et al., 2009), from reduction in worldwide marine primary productivity (D'Hondt et al., 1998; Aberhan et al., 2007; Maruoka et al., 2007), and from degassing of mantle volatiles during several short eruptions of the Deccan Traps (Courtillot et al., 1986; Officer et al., 1987; Self et al., 2006; Kring, 2007; Chenet et al., 2009). Estimated atmospheric CO 2 concentrations across the K–T transition are tests of these hypotheses. "
[Show abstract][Hide abstract] ABSTRACT: A dramatic change in atmospheric composition has been postulated because of global carbon cycle disruption during the Cretaceous (K)–Tertiary (T) transition following the Chicxulub impact and Deccan Trap eruptions. Here, pedogenic carbonates were collected fromdrill core of a borehole (SK-1 (N)) straddling the Late Cretaceous and early Paleocene strata in the Songliao Basin, northeast China, to reconstruct atmospheric CO2 concentrations using a paleosol paleobarometer. Our estimates for atmospheric pCO2 from paleosol carbonates range between 277±115 ppmv and 837±164 ppmv between 67.8 Ma and 63.1 Ma. One large (~66–65.5 Ma) and several small CO2 spikes (~64.7–~64.2 Ma) during the latest Maastrichtian to earliest Danian are reported here and incorporatedwith previously published pCO2 estimates also estimated frompaleosol carbonates. These CO2 spikes are attributed to one-million-year-long emplacement of the large Deccan flood basalts along with the extraterrestrial impact at the K–T boundary.
"1. Introduction  The K-Pg extinction that followed the Chicxulub impact was one of the five great Phanerozoic marine mass extinctions in terms of both loss of genera and the restructuring of communities [Sepkoski, 2002; Rohde and Muller, 2005; McGhee et al., 2004, 2013; Sheehan et al., 1996]. A heat pulse and subsequent fires appear to explain terrestrial species extinctions following the asteroid impact [Melosh et al., 1990; Wolbach et al., 1988; Robertson et al., 2004; 2013]. Those heat effects would have had little direct effect on aquatic environments because water would provide shelter from the impact-generated heat pulse, but the subsequent " impact winter " is another matter altogether. "
[Show abstract][Hide abstract] ABSTRACT: The Chicxulub asteroid impact produced massive extinction in terrestrial environments
most likely through an intense heat pulse and subsequent widespread fires. Aquatic
environments were shielded from this heat and fire but nevertheless showed massive
extinction in marine environments and, for reasons unexplained, far less extinction in
freshwater environments. Extinction in marine environments resulted from the effects of an
“impact winter” caused by dust and smoke in the atmosphere that extinguished sunlight at
the Earth’s surface for a period of months to years. The resulting cessation of photosynthesis
caused a globally extensive extinction of phytoplankton taxa. Because aquatic ecosystems,
unlike terrestrial environments, are strongly dependent on daily photosynthetic output by
autotrophs, loss of phytoplankton likely caused catastrophic mortality and extinction in
aquatic ecosystems. Other potential causes of mortality in aquatic ecosystems include lower
ambient temperatures and anoxia due to the lack of photosynthetic oxygen. Inland waters,
although probably subject to high mortality, showed lower proportionate extinction than
marine environments probably because of the greater potential among the freshwater taxa for
dormancy, the greater efficiency of reaeration by rapid flow to offset oxygen demand,
abundant thermal refugia fed by groundwater at moderate temperatures, and preadaptation of
freshwater taxa to a great degree of environmental variability. In addition, detrital feeders
appear to have had low extinction rates in either marine or freshwater environments, but
again freshwater taxa would have been favored by higher renewal rates of detrital organic
matter as a result of their direct hydrologic contact with soil.
Full-text · Article · Jul 2013 · Journal of Geophysical Research Atmospheres
"Their kinetic energy was converted upon reentry to IR radiation [Melosh et al., 1990]. This energy would have been approximately equal to 1 Mt hydrogen bomb explosions at 6 km spacing around the entire planet. "
[Show abstract][Hide abstract] ABSTRACT: 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.
Full-text · Article · Mar 2013 · Journal of Geophysical Research Atmospheres