“Lucifer’s Hammer killed the dinosaurs”

Lucifer’s Hammer Hardcover (1977)

The end of the Mesozoic era at ca. 66 million years ago (Ma) is marked by one of the most severe biotic crisis in Earth’s history: the Cretaceous-Paleogene (K-Pg) mass extinction. During the event, three-quarters of the plant and animal species on Earth disappeared, including non-avian dinosaurs, pterosaurs, marine reptiles, ammonites, and planktonic foraminifera. Two planetary scale disturbances were linked to this mass extinction event: the eruption of the Deccan Traps large igneous province, and the collision of an asteroid of more than 10 km in diameter with the Yucatan Peninsula.

“Lucifer’s Hammer”, written by Larry Niven and Jerry Pournelle, was the first major science fiction novel to try to deal realistically with the planetary emergency of an impact event. It was published in 1977. Almost at the same time, the discovery of anomalously high abundance of iridium and other platinum group elements in the Cretaceous/Palaeogene (K-Pg) boundary led to the hypothesis that an asteroid collided with the Earth and caused one of the most devastating events in the history of life.

Gravity anomaly map of the Chicxulub impact structure (From Wikimedia Commons)

“Lucifer’s Hammer killed the dinosaurs,” said US physicist Luis Alvarez, in a lecture on the geochemical evidence he and his son found of a massive impact at the end of the Cretaceous period. A year later, Pemex (a Mexican oil company) identified Chicxulub as the site of this massive asteroid impact. The crater is more than 180 km (110 miles) in diameter and 20 km (10 miles) in depth. The impact released an estimated energy equivalent of 100 teratonnes of TNT, induced earthquakes, shelf collapse around the Yucatan platform, and widespread tsunamis that swept the coastal zones of the surrounding oceans.

The event also produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere. Global forest fires might have raged for months. Photosynthesis stopped and the food chain collapsed. The combination of dust and aerosols precipitated a severe impact winter in the decades after impact. Ocean acidification was the trigger for mass extinction in the marine realm. Acidification affects the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus in the ocean and interferes with a range of processes including growth, calcification, development, reproduction and behaviour in a wide range of marine organisms like planktonic coccolithophores, foraminifera, echinoderms, corals, and coralline algae. Additionaly, ocean acidification can intensify the effects of global warming, in a dangerous feedback loop.

The Deccan traps

Early work speculated that the Chicxulub impact triggered large-scale mantle melting and initiated the Deccan flood basalt eruption. Precise dating of both, the impact and the flood basalts, show that the earliest eruptions of the Deccan Traps predate the impact. But, the Chicxulub impact, and the enormous Wai Subgroup lava flows of the Deccan Traps continental flood basalts appear to have occurred very close together in time. Marine volcanism also provides a potential source of oceanic acidification, but a recemt study by Yale University indicates that the sudden ocean acidification was caused by the Chicxulub bolide impact (and not by the volcanic activity) that vaporised rocks containing sulphates and carbonates, causing sulphuric acid and carbonic acid to rain down. The evidence came from the shells of planktic and benthic foraminifera. More recently, a new study focused on carbon cycle modeling and paleotemperature records shows that the Chicxulub impact was the primary driver of the end-Cretaceous mass extinction.The global temperature compilation reveals that ~50% of Deccan Trap CO2 outgassing occurred well before the impact. Additionalty, the Late Cretaceous warming event attributed to Deccan degassing is of a comparable size to small warming events in the Paleocene and early Eocene.

References:
P.M. Hull et al., “On impact and volcanism across the Cretaceous-Paleogene boundary,” Science (2019). Vol. 367, Issue 6475, pp. 266-272 https://science.sciencemag.org/content/367/6475/266

Alvarez, L., W. Alvarez, F. Asaro, and H.V. Michel. 1980. Extraterrestrial cause for the Cretaceous-Tertiary extinction: Experimental results and theoretical interpretation. Science 208:1095–1108.

Michael J. Henehan el al., “Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact,” PNAS (2019). www.pnas.org/cgi/doi/10.1073/pnas.1905989116

Ocean acidification and the end-Cretaceous mass extinction

Heterohelix globulosa foraminifera isolated from the K-Pg boundary clay at Geulhemmerberg in the Netherlands. Image credit: Michael J. Henehan/PNAS

The Cretaceous–Paleogene extinction that followed the Chicxulub impact was one of the five great Phanerozoic mass extinctions. Three-quarters of the plant and animal species on Earth disappeared, including non-avian dinosaurs, pterosaurs, marine reptiles, ammonites, and planktonic foraminifera. The impact released an estimated energy equivalent of 100 teratonnes of TNT, induced earthquakes, shelf collapse around the Yucatan platform, and widespread tsunamis that swept the coastal zones of the surrounding oceans. The event also produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere. Global forest fires might have raged for months. Photosynthesis stopped and the food chain collapsed. The impacto also caused sudden ocean acidification, impacting marine ecosystems and the carbon cycle. Around the time of the impact, 23,000 to 230,000 cubic miles of magma erupted out of the mid-ocean ridges, all over the globe. One of the largest eruptive events in Earth’s history. This pulse of global marine volcanism played an important role in the environmental crisis at the end of the Cretaceous. Marine volcanism also provides a potential source of oceanic acidification, but a new study by Yale University indicates that the sudden ocean acidification was caused by the Chicxulub bolide impact (and not by the volcanic activity) that vaporised rocks containing sulphates and carbonates, causing sulphuric acid and carbonic acid to rain down. The evidence came from the shells of planktic and benthic foraminifera.

Foraminifera are crucial elements for our understanding of past and present oceans. Their skeletons take up chemical signals from the sea water, in particular isotopes of oxygen and carbon. Over millions of years, these skeletons accumulate in the deep ocean to become a major component of biogenic deep-sea sediments. Ocean acidification in the geological record is often inferred from a decrease in the accumulation and preservation of CaCO3 in marine sediments, potentially indicated by an increased degree of fragmentation of foraminiferal shells. In the early 1990’s it was recognised that the boron isotopic composition of marine carbonates was determined largely by ocean pH. Usingy the boron isotope-pH proxy to planktic and benthic foraminifera, the new study determinated the ocean pH drop following the Chicxulub impact.

The Cretaceous/Palaeogene extinction boundary clay at Geulhemmerberg Cave. Image credit: Michael J. Henehan

The boron isotope composition of carbonate samples obtained from a shallow-marine sample site (Geulhemmerberg Cave, The Netherlands) preserved sediments from the first 100 to 1000 years after the asteroid’s impact. The data from the Geulhemmerberg Cave indicate a marked ∼0.25 pH unit surface ocean acidification event within a thousand years. This change in pH corresponds to a rise in atmospheric partial pressure of CO2 (pCO2) from ∼900 ppm in the latest Maastrichtian to ∼1,600 ppm in the immediate aftermath of bolide impact.

Ocean acidification was the trigger for mass extinction in the marine realm. Acidification affects the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus in the ocean and interferes with a range of processes including growth, calcification, development, reproduction and behaviour in a wide range of marine organisms like planktonic coccolithophores, foraminifera, echinoderms, corals, and coralline algae. Additionaly, ocean acidification can intensify the effects of global warming, in a dangerous feedback loop.

Anthropogenic climate change and ocean acidification resulting from the emission of vast quantities of CO2 and other greenhouse gases pose a considerable threat to ecosystems and modern society. Since the Industrial Revolution the pH within the ocean surface has decreased ~0.1 pH and is predicted to decrease an additional 0.2 – 0.3 units by the end of the century. This underlines the urgency for immediate action on global carbon emission reductions.

 

 

References:

Michael J. Henehan el al., “Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact,” PNAS (2019). www.pnas.org/cgi/doi/10.1073/pnas.1905989116

Kump, L.R., T.J. Bralower, and A. Ridgwell. 2009. Ocean acidification in deep time. Oceanography 22(4):94–107, https://doi.org/10.5670/oceanog.2009.100.

 

Aftermath: The first day of the Cenozoic

Gravity anomaly map of the Chicxulub impact structure (From Wikimedia Commons)

In the late ’70, the discovery of anomalously high abundance of iridium and other platinum group elements in the Cretaceous/Palaeogene (K-Pg) boundary led to the hypothesis that an asteroid collided with the Earth and caused one of the most devastating events in the history of life. In 1981, Pemex (a Mexican oil company) identified Chicxulub as the site of this massive asteroid impact. The crater is more than 180 km (110 miles) in diameter and 20 km (10 miles) in depth, making the feature one of the largest confirmed impact structures on Earth. The Cretaceous–Paleogene extinction that followed the Chicxulub impact was one of the five great Phanerozoic mass extinctions. The impact released an estimated energy equivalent of 100 teratonnes of TNT, induced earthquakes, shelf collapse around the Yucatan platform, and widespread tsunamis that swept the coastal zones of the surrounding oceans. The event also produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere. Global forest fires might have raged for months. Photosynthesis stopped and the food chain collapsed.

The Chicxulub impact site is the only known impact structure on Earth with an unequivocal peak ring but it is buried and only accessible through drilling. In April to May 2016, a team by International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) drilled the Chicxulub peak ring offshore. The core recovered during the expedition provides a window into the immediate aftermath of the impact.

Timeline of events recorded inside the impact crater.

The recovered core was divided into 4 Units. The Unit 1 is 111.63-m-thick postimpact sedimentary rock. The Unit 2 is 104.28-m thick and dominantly suevite. The Unit 3 is 25.41-m-thick impact melt rock, with some clasts present. The Unit 4 consists of shocked granitic target rocks, preimpact sheet intrusions, and intercalations of suevite and impact melt rock. There are high abundances of charcoal in Unit 1. The charcoal likely originated from impact-related combustion of forested landscapes surrounding the Gulf of Mexico. Data indicate that Chicxulub impact released sufficient thermal radiation to ignite flora up to 1,000 to 1,500 km from the impact site. The upper few centimeters of the unit 2 contain abundant reworked Maastrichtian planktic foraminifera that indicate redeposition of sediments that were unconsolidated at the time of the impact.

The lack of evaporites in the recovered sedimentary section, supports the impact generated sulfate aerosol production and extinction mechanisms, including global cooling and limitations on photosynthesis. Core samples also revealed that a high-temperature hydrothermal system was established within the crater but the appearance of burrowing organisms within years of the impact indicates that the hydrothermal system did not adversely affect seafloor life. These impact-generated hydrothermal systems are hypothesized to be potential habitats for early life on Earth and other planets.

 

References:

Sean P. S. Gulick, Timothy J. Bralower, Jens Ormö, Brendon Hall, Kliti Grice, Bettina Schaefer, Shelby Lyons, Katherine H. Freeman, Joanna V. Morgan, Natalia Artemieva, Pim Kaskes, Sietze J. de Graaff, Michael T. Whalen, Gareth S. Collins, Sonia M. Tikoo, Christina Verhagen, Gail L. Christeson, Philippe Claeys, Marco J. L. Coolen, Steven Goderis, Kazuhisa Goto, Richard A. F. Grieve, Naoma McCall, Gordon R. Osinski, Auriol S. P. Rae, Ulrich Riller, Jan Smit, Vivi Vajda, Axel Wittmann, and the Expedition 364 Scientists. The first day of the Cenozoic. PNAS, 2019 DOI: 10.1073/pnas.1909479116

Morgan, J. V., Gulick, S. P. S., Bralower, T., Chenot, E., Christeson, G., Claeys, P., … Zylberman, W. (2016). The formation of peak rings in large impact craters. Science, 354(6314), 878–882. doi:10.1126/science.aah6561

Christopher M. Lowery et al. Rapid recovery of life at ground zero of the end-Cretaceous mass extinction, Nature (2018). DOI: 10.1038/s41586-018-0163-6

Life finds a way.

 

Site M0077 in the Chicxulub crater as seen using gravity data. From Lowery et al., 2018.

In the late ’70, the discovery of anomalously high abundance of iridium and other platinum group elements in the Cretaceous/Palaeogene (K-Pg) boundary led to the hypothesis that an asteroid collided with the Earth and caused one of the most devastating events in the history of life. In 1981, Pemex (a Mexican oil company) identified Chicxulub as the site of this massive asteroid impact. The crater is more than 180 km (110 miles) in diameter and 20 km (10 miles) in depth, making the feature one of the largest confirmed impact structures on Earth.

The impact released an estimated energy equivalent of 100 teratonnes of TNT, induced earthquakes, shelf collapse around the Yucatan platform, and widespread tsunamis that swept the coastal zones of the surrounding oceans. The event also produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere. The decrease of sunlight caused a drastic short-term global reduction in temperature (15 °C on a global average, 11 °C over the ocean, and 28 °C over land). While the surface and lower atmosphere cooled, the tropopause became much warmer, eliminate the tropical cold trap and allow water vapor mixing ratios to increase to well over 1,000 ppmv in the stratosphere. Those events accelerated the destruction of the ozone layer. During this period, UV light was able to reach the surface at highly elevated and harmful levels. Additionally, the vapour produced by the impact  could have led to global acid rain and a dramatic acidification of marine surface waters.

The Cretaceous/Palaeogene mass extinction eradicated almost three-quarters of the plant and animal species on Earth including non-avian dinosaurs, pterosaurs, marine reptiles, and ammonites. Global forest fires might have raged for months. Photosynthesis stopped and the food chain collapsed. Marine environments lost about half of their species, and almost 90% of Foraminifera species went extinct. But life always finds a way, and 30,000 years after the impact, a thriving ecosystem was present within the Chicxulub crater.

The evidence comes from the recent joint expedition of the International Ocean Discovery Program and International Continental Drilling Program. The team sampled the first record of the few hundred thousand years immediately after the impact within the Chicxulub crater. This sample includes foraminifera, calcareous nannoplankton, trace fossils and geochemical markers for high productivity. The lowermost part of the limestone sampled also contains the lowest occurrence of Parvularugoglobigerina eugubina, the first trochospiral planktic foraminifera, which marks the base of Zone Pα. This biozone was defined at Gubbio (Italy) to precisely characterise the Cretaceous/Paleogene boundary.

3 Early Danian foraminifer abundances and I/(Ca+Mg) oxygenation proxy. From Lowery et al., 2018.

P. eugubina was a low to middle latitude taxon with an open-ocean affinity and has an extremely variable morphology. Other foraminifer of the same genus (P. extensa, P. alabamensis) and Guembelitria cretacea were found at the same core. The nannofossil assemblage includes opportunistic groups that can tolerate high environmental stress such as Thoracosphaera and Braarudosphaera, but unlike the foraminifera, there are no clear stratigraphic trends in overall nannoplankton abundance. Discrete, but clear trace fossils, including Planolites and Chondrites, characterize the upper 20cm of the transitional unit. Nevertheless, the study also shows that photosynthetic phytoplankton struggled to recover for millions of years after the event.

Core samples also revealed that porous rocks in the center of the Chicxulub crater had remained hotter than 300 °C for more than 100,000 years. The high-temperature hydrothermal system was established within the crater but the appearance of burrowing organisms within years of the impact indicates that the hydrothermal system did not adversely affect seafloor life. These impact-generated hydrothermal systems are hypothesized to be potential habitats for early life on Earth and other planets.

 

Reference:

Christopher M. Lowery et al. Rapid recovery of life at ground zero of the end-Cretaceous mass extinction, Nature (2018). DOI: 10.1038/s41586-018-0163-6

Charles G. Bardeen, Rolando R. Garcia, Owen B. Toon, and Andrew J. Conley, On transient climate change at the Cretaceous−Paleogene boundary due to atmospheric soot injections, PNAS 2017 ; published ahead of print August 21, 2017 DOI: 10.1073/pnas.1708980114

Brugger J.G. Feulner, and S. Petri (2016), Baby, it’s cold outside: Climate model simulations of the effects of the asteroid impact at the end of the CretaceousGeophys. Res. Lett.43,  doi:10.1002/2016GL072241.

 

 

Volcanism, the Chicxulub impact and the K-Pg event.

The Deccan traps

It was the best of times. It was the worst of times. The end of the Mesozoic era at ca. 66 million years ago (Ma) is marked by one of the most severe biotic crisis in Earth’s history: the Cretaceous-Paleogene (K-Pg) mass extinction. During the event, three-quarters of the plant and animal species on Earth disappeared, including non-avian dinosaurs, other vertebrates, marine reptiles and invertebrates, planktonic foraminifera and ammonites. Marine ecosystems lost about half of their species while freshwater environments shows low extinction rates, about 10% to 22% of genera.

Two events were linked to this mass extinction: the eruption of the Deccan Traps large igneous province, and the Chicxulub meteorite impact. Early work speculated that the Chicxulub impact triggered large-scale mantle melting and initiated the Deccan flood basalt eruption. Precise dating of both, the impact and the flood basalts, show that the earliest eruptions of the Deccan Traps predate the impact. But, the Chicxulub impact, and the enormous Wai Subgroup lava flows of the Deccan Traps continental flood basalts appear to have occurred very close together in time. Recent studies suggest a possible association between the Chicxulub impact and variations in the progression of Deccan Traps eruptions. Seismic modeling indicates that the impact could have generated seismic energy densities of order 0.1–1.0 J/m3 throughout the upper ∼200 km of Earth’s mantle, sufficient to trigger volcanic eruptions worldwide.

Gravity anomaly map of the Chicxulub impact structure (From Wikimedia Commons)

The oceanic crust records the history of temporal variations in seafloor magmatism continuously and at high resolution through geologic time. Around the time of the Chicxulub impact, 23,000 to 230,000 cubic miles of magma erupted out of the mid-ocean ridges, all over the globe. One of the largest eruptive events in Earth’s history. This pulse of global marine volcanism played an important role in the environmental crisis at the end of the Cretaceous, through magmatism by extruding large volumes of basalt and releasing volcanic gases or through enhanced hydrothermal venting driven by magmatic intrusion. Marine volcanism also provides a potential source of oceanic acidification.

The Chicxulub impact released an estimated energy equivalent of 100 teratonnes of TNT and produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere. The decrease of sunlight caused a drastic short-term global reduction in temperature (15 °C on a global average, 11 °C over the ocean, and 28 °C over land). While the surface and lower atmosphere cooled, the tropopause became much warmer, eliminate the tropical cold trap and allow water vapor mixing ratios to increase to well over 1,000 ppmv in the stratosphere. Those events accelerated the destruction of the ozone layer. During this period, UV light was able to reach the surface at highly elevated and harmful levels.

 

References:

Joseph S. Byrnes and Leif Karlstrom, Anomalous K-Pg–aged seafloor attributed to impact-induced mid-ocean ridge magmatism, Sci Adv 4 (2), eaao2994, DOI: 10.1126/sciadv.aao2994

Charles G. Bardeen, Rolando R. Garcia, Owen B. Toon, and Andrew J. Conley, On transient climate change at the Cretaceous−Paleogene boundary due to atmospheric soot injections, PNAS 2017 ; published ahead of print August 21, 2017 DOI: 10.1073/pnas.1708980114

The Winds of Winter

Gravity anomaly map of the Chicxulub impact structure (From Wikimedia Commons)

Almost thirty years ago, the discovery of anomalously high abundance of iridium and other platinum group elements in the Cretaceous/Palaeogene (K-Pg) boundary led to the hypothesis that an asteroid collided with the Earth and caused one of the most devastating events in the history of life. The impact created the 180-kilometre wide Chicxulub crater causing widespread tsunamis along the coastal zones of the surrounding oceans and released an estimated energy equivalent of 100 teratons of TNT and produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere.

Three-quarters of the plant and animal species on Earth disappeared, including non-avian dinosaurs, other vertebrates, marine reptiles and invertebrates, planktonic foraminifera and ammonites. Marine ecosystems lost about half of their species while freshwater environments shows low extinction rates, about 10% to 22% of genera.

A time-lapse animation showing severe cooling due to sulfate aerosols from the Chicxulub asteroid impact 66 million years ago (Credit: PKI)

The decrease of sunlight caused a drastic short-term global reduction in temperature (15 °C on a global average, 11 °C over the ocean, and 28 °C over land). While the surface and lower atmosphere cooled, the tropopause became much warmer, eliminate the tropical cold trap and allow water vapor mixing ratios to increase to well over 1,000 ppmv in the stratosphere. Those events accelerated the destruction of the ozone layer. During this period, UV light was able to reach the surface at highly elevated and harmful levels. This phenomenon is called “impact winter”.

Recent drilling of the peak ring of the Chicxulub impact crater has been used to create 3-D numerical simulations of the crater formation. It was estimate that the angle of impact at Chicxulub was ~60° with a downrange direction to the southwest. The new study indicates that the impact may have released around three times as much sulfur and much less carbon dioxide compared with previous calculations, suggesting that surface temperatures were likely to have been significantly reduced for several years and ocean temperatures affected for hundreds of years after the Chicxulub impact.

 

References:

Artemieva, N., Morgan, J., & Expedition 364 Science Party (2017). Quantifying the release of climate-active gases by large meteorite impacts with a case study of Chicxulub. Geophysical Research DOI: 10.1002/2017GL074879

 

Charles G. Bardeen, Rolando R. Garcia, Owen B. Toon, and Andrew J. Conley, On transient climate change at the Cretaceous−Paleogene boundary due to atmospheric soot injections, PNAS 2017 ; published ahead of print August 21, 2017 DOI: 10.1073/pnas.1708980114

Brugger J.G. Feulner, and S. Petri (2016), Baby, it’s cold outside: Climate model simulations of the effects of the asteroid impact at the end of the CretaceousGeophys. Res. Lett.43,  doi:10.1002/2016GL072241.

 

Dark skies at the end of the Cretaceous

A time-lapse animation showing severe cooling due to sulfate aerosols from the Chicxulub asteroid impact 66 million years ago (Credit: PKI)

Thirty years ago, the discovery of anomalously high abundance of iridium and other platinum group elements in the Cretaceous/Palaeogene (K-Pg) boundary led to the hypothesis that an asteroid collided with the Earth and caused one of the most devastating events in the history of life. The impact created the 180-kilometre wide Chicxulub crater causing widespread tsunamis along the coastal zones of the surrounding oceans and released an estimated energy equivalent of 100 teratons of TNT and produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere. Three-quarters of the plant and animal species on Earth disappeared. Marine ecosystems lost about half of their species while freshwater environments shows low extinction rates, about 10% to 22% of genera.

Recent studies suggest that the amount of sunlight that reached Earth’s surface was reduced by approximately 20%. Photosynthesis stopped and the food chain collapsed. The decrease of sunlight caused a drastic short-term global reduction in temperature (15 °C on a global average, 11 °C over the ocean, and 28 °C over land). While the surface and lower atmosphere cooled, the tropopause became much warmer, eliminate the tropical cold trap and allow water vapor mixing ratios to increase to well over 1,000 ppmv in the stratosphere. Those events accelerated the destruction of the ozone layer. During this period, UV light was able to reach the surface at highly elevated and harmful levels.

Gravity anomaly map of the Chicxulub impact structure (From Wikimedia Commons)

In 1980, Walter Alvarez and his father, Luis Alvarez ignited a huge controversy when they concluded that the anomalous iridium concentration at the K-Pg boundary is best interpreted as the result of an asteroid impact. They even calculated the size of the asteroid (about 7 km in diameter) and the crater that this body might have caused (about 100–200 km across). In 1981, Pemex (a Mexican oil company) identified Chicxulub as the site of a this massive asteroid impact. The crater is more than 180 km (110 miles) in diameter and 20 km (10 miles) in depth, making the feature one of the largest confirmed impact structures on Earth.

 

References:

Charles G. Bardeen, Rolando R. Garcia, Owen B. Toon, and Andrew J. Conley, On transient climate change at the Cretaceous−Paleogene boundary due to atmospheric soot injections, PNAS 2017 ; published ahead of print August 21, 2017 DOI: 10.1073/pnas.1708980114

Brugger J.G. Feulner, and S. Petri (2016), Baby, it’s cold outside: Climate model simulations of the effects of the asteroid impact at the end of the CretaceousGeophys. Res. Lett.43,  doi:10.1002/2016GL072241.

Climate model simulations at the end of the Cretaceous.

gg_60212w_crater

Artist’s reconstruction of Chicxulub crater 66 million years ago.

About thirty years ago, the discovery of anomalously high abundance of iridium and other platinum group elements in the Cretaceous/Palaeogene (K-Pg) boundary led to the hypothesis that a 10 km asteroid collided with the Earth and caused one of the most devastating events in the history of life. The impact created the 180-kilometre wide Chicxulub crater causing widespread tsunamis along the coastal zones of the surrounding oceans and released an estimated energy equivalent of 100 teratons of TNT and produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere.

To model the climatic effects of the impact, a team of scientist from the Potsdam Institute for Climate Impact Research (PIK), use literature information from geophysical impact modeling indicating that for a 2.9 km thick target region consisting of 30% evaporites and 70% water-saturated carbonates and a dunite projectile with 50% porosity, a velocity of 20 km/s and a diameter between 15 and 20 km, a sulfur mass of 100 Gt is produced. This is about 10,000 times the amount of sulfur released during the 1991 Pinatubo eruption. Additionally, for a sulfur mass of 100 Gt, about 1400 Gt of carbon dioxide are injected into the atmosphere, corresponding to an increase of the atmospheric CO2 concentration by 180 ppm. There could be additional CO2 emissions from ocean outgassing and perturbations of the terrestrial biosphere, adding a total of 360 ppm and 540 ppm of CO2. The main result is a severe and persistent global cooling in the decades after the impact. Global annual mean temperatures over land dropped to -32C in the coldest year and continental temperatures in the tropics reaching a mere -22C. This model is supported by a migration of cool, boreal dinoflagellate species into the subtropic Tethyan realm directly across the K–Pg boundary interval and the ingression of boreal benthic foraminifera into the deeper parts of the Tethys Ocean, interpreted to reflect millennial timescale changes in the ocean circulation after the impact (Vellekoop, 2014).

A time-lapse animation showing severe cooling due to sulfate aerosols from the Chicxulub asteroid impact 66 million years ago (Credit: PKI)

A time-lapse animation showing severe cooling due to sulfate aerosols from the Chicxulub asteroid impact 66 million years ago (Credit: PKI)

References:

Brugger J., G. Feulner, and S. Petri (2016), Baby, it’s cold outside: Climate model simulations of the effects of the asteroid impact at the end of the Cretaceous, Geophys. Res. Lett., 43,  doi:10.1002/2016GL072241.

Alvarez, L. W., W. Alvarez, F. Asaro, and H. V. Michel (1980), Extraterrestrial Cause for the Cretaceous-Tertiary Extinction, Science, 208 (4448), 1095{1108, doi: 10.1126/science.208.4448.1095.

Galeotti, S., H. Brinkhuis, and M. Huber (2004), Records of post Cretaceous-Tertiary boundary millennial-scale cooling from the western Tethys: A smoking gun for the impact-winter hypothesis?, Geology, 32, 529, doi:10.1130/G20439.1

Johan Vellekoop, Appy Sluijs, Jan Smit, Stefan Schouten, Johan W. H. Weijers, Jaap S. Sinningh Damsté, and Henk Brinkhuis, Rapid short-term cooling following the Chicxulub impact at the Cretaceous–Paleogene boundary, PNAS (2014) doi: 10.1073/pnas.1319253111