“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

Mutagenesis in land plants during the end-Triassic mass extinction

 

A basaltic lava flow section from the Middle Atlas, Morocco. From Wikimedia Commons.

During the last 540 million years five mass extinction events shaped the history of the Earth. The End-Triassic Extinction at 201.51 million years (Ma) is probably the least understood of these events. Most mammal-like reptiles and large amphibians disappeared, as well as early dinosaur groups. In the oceans, this event eliminated conodonts and nearly annihilated corals, ammonites, brachiopods and bivalves. In the Southern Hemisphere, the vegetation turnover consisted in the replacement to Alisporites (corystosperm)-dominated assemblage to a Classopollis (cheirolepidiacean)-dominated one.

The mass extinction event was likely caused by the eruption of the Central Atlantic Magmatic Province (CAMP), a large igneous province emplaced during the initial rifting of Pangea. Data indicates that magmatic activity started c. 100,000 years before the endTriassic event and continued in pulses for 700,000 years. The CO2 emissions caused global warming. The SO2 emissions on mixing with water vapour in the atmosphere, caused acid rain, which in turn killed land plants and caused soil erosion.

A normal fern spore compared with mutated ones from the end-Triassic mass extinction event. Image credit: S LINDSTRÖM, GEUS

Volcanoes are also a primary source of mercury (Hg) in the global atmosphere. Mercury can cause morphologically visible abnormalities in plants and their reproductive cells (spores and pollen). A new study led by Sofie Lindström of the Geological Survey of Denmark and Greenland analized various types of abnormalities in the reproductive cells of ferns, with focus in two morphogroups: LTT-spores (laevigate, trilete fern spores with thick exine), and LCT-spores (laevigate, circular, trilete spores). The LTT-spores were produced primarily by the fern families Dipteridaceae, Dicksoniaceae, and Matoniaceae, while LCT spores were primarily produced by ferns belonging to Osmundaceae and Marattiales.

The elevated concentrations of mercury (Hg) in sedimentary rocks in North America, Greenland, England, Austria, Morocco, and Peru are linked to CAMP eruptions. This pulse of mercury also correlate with high occurrences of abnormal fern spores, indicating severe environmental stress and genetic disturbance in the parent plants. Three negative organic C-isotope excursions (CIEs) have being recognized at the end-Triassic: the Marshi, the Spelae, and the top-Tilmanni CIEs. Malformations in LTT-spores first occur sporadically in the lower pre-Marshi interval. LCT-spores are present but are generally rare in this interval. During the Spelae CIE, the occurrences of moderate to severe malformations increased and aberrant forms can encompass as much as 56% of the counted LTT-spores. This interval is associated with marked global warming, recorded by stomatal proxy data.

 

 

References:

Sofie Lindström et al. Volcanic mercury and mutagenesis in land plants during the end-Triassic mass extinction, Science Advances (2019). DOI: 10.1126/sciadv.aaw4018}

Grasby, S. E., Them, T. R., Chen, Z., Yin, R., & Ardakani, O. H. (2019). Mercury as a proxy for volcanic emissions in the geologic record. Earth-Science Reviews, 102880. doi:10.1016/j.earscirev.2019.102880

Learning from Past Climate Changes

In the last 540 million years, five mass extinction events shaped the history of the Earth. Those events were related to extreme climatic changes and were mainly caused by asteroid impacts, massive volcanic eruption, or the combination of both.  On a global scale the main forces behind climatic change are: solar forcing, atmospheric composition, plate tectonics, Earth’s biota, and of course, us. Human activity is a major driver of the dynamics of Earth system. From hunter-gatherer and agricultural communities to the highly technological societies of the 21st century, humans have driven the climate Earth system towards new, hotter climatic conditions. Until the Industrial Revolution, the average global CO2 levels fluctuated between about 170 ppm and 280 ppm. But with the beginning of the Industrial Era, that number risen above 300 ppm, currently averaging an increase of more than 2 ppm per year. The average monthly level of CO2 in the atmosphere in last April exceeded the 410 ppm for first time in history. Thus we could hit an average of 500 ppm within the next 45 years, a number that has been unprecedented for the past 50–100+ million years according to fossil plant-based CO2 estimates. This current human-driven change far exceed the rates of change driven by geophysical or biosphere forces that have altered the Earth System trajectory in the past, and it poses severe risks for health, economies and political stability. Learning from past climatic changes is critical to our future.

Planktonic foraminifera from the Sargasso Sea in the North Atlantic Ocean. (Photograph courtesy Colomban de Vargas, EPPO/SBRoscoff.)

Microfossils from deep-sea are crucial elements for the understanding of our 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. The importance of microfossils as tool for paleoclimate reconstruction was recognized early in the history of oceanography. John Murray, naturalist of the CHALLENGER Expedition (1872-1876) found that differences in species composition of planktonic foraminifera from ocean sediments contain clues about the temperatures in which they lived. The ratio of heavy and light Oxygen in foraminifera shells can reveal how cold the ocean was and how much ice existed at the time the shell formed. Another tool to reconstruct paleotemperatures is the ratio of magnesium to calcium (Mg/Ca) in foraminiferal shells. Mg2+ incorporation into foraminiferal calcite  is influenced by the temperature of the surrounding seawater, and the Mg/Ca ratios increase with increasing temperature.

Diatoms and radiolarians are susceptible to different set of dissolution parameters than calcareous fossils, resulting in a different distribution pattern at the sea floor and have been used for temperature estimates in the Pacific and in the Antarctic Oceans, especially where calcareous fossils are less abundant. Diatom assemblages are also used in reconstructions of paleoproductivity.

Scanning electron microscope image of different types of pollen grains. Image from Wikipedia.

Pollen and other palynomorphs proved to be an extraordinary tool to paleoenvironmental reconstruction too. Pollen analysis involves the quantitative examination of spores and pollen at successive horizons through a core, specially in lake, marsh or delta sediments, especially in Quaternary sediments where the parent plants are well known. This provide information on regional changes in vegetation through time, and it’s also a valuable tool for archaeologists because it gives clues about man’s early environment and his effect upon it.

Stomatal frequency of land plants, which has been shown in some species to vary inversely with atmospheric pCO2, has been used to estimate paleo-pCO2 for multiple geological time periods. Stomata are the controlled pores through which plants exchange gases with their environments, and play a key role in regulating the balance between photosynthetic productivity and water loss through transpiration.

Temple I on The Great Plaza and North Acropolis seen from Temple II in Tikal, Guatemala. From Wikimedia Commons

Paleoecological records indicate that the transition to agriculture was a fundamental turning point in the environmental history of Mesoamerica. Tropical forests were reduced by agricultural expansion associated with growing human populations. Also soil loss associated with deforestation and erosion was one of the most consequential environmental impacts associated with population expansion in the Maya lowlands. This environmental crisis ended with the collapse of the Classic Maya society.

Human activity has significantly altered the climate in less than a century. Since 1970 the global average temperature has been rising at a rate of 1.7°C per century, and the rise in global CO2 concentration since 2000 is 10 times faster than any sustained rise in CO2 during the past 800,000 years. Today the most politically unstable countries are also places where environmental degradation affected food production and water supply. Other human societies have succumbed to climate change – like the Akkadians – while others have survived by changing their behavior in response to environmental change. We have the opportunity to protect the future of our own society by learning from the mistakes of our ancestors.

References:

David Evans, Navjit Sagoo, Willem Renema, Laura J. Cotton, Wolfgang Müller, Jonathan A. Todd, Pratul Kumar Saraswati, Peter Stassen, Martin Ziegler, Paul N. Pearson, Paul J. Valdes, Hagit P. Affek. Eocene greenhouse climate revealed by coupled clumped isotope-Mg/Ca thermometry. Proceedings of the National Academy of Sciences, 2018; 201714744 DOI: 10.1073/pnas.1714744115

Nicholas P. Evans et al., Quantification of drought during the collapse of the classic Maya civilization, Science (2018); DOI: 10.1126/science.aas9871 

Will Steffen, et al.; Trajectories of the Earth System in the Anthropocene; PNAS (2018) DOI: 10.1073/pnas.1810141115

On the rise of the archosauromorphs

Proterosaurus speneri at Teyler’s Museum.

In the aftermath of the devastating Permo-Triassic mass extinction (~252 Ma), synapsid groups such as anomodonts and gorgonopsians and parareptiles such as pareiasaurs, were decimated and largely displaced by the archosauromorphs. The group, which include the ‘ruling reptiles’ (crocodylians, pterosaurs, dinosaurs, and their descendants, birds), originated during the middle–late Permian. The most basal archosauromorphs are Aenigmastropheus and Protorosaurus.

During the Triassic, the archosauromorphs achieved high morphological diversity, including aquatic or semi aquatic forms, highly specialized herbivores, massive predators, armoured crocodile-like forms, and gracile dinosaur precursors. The group constitutes an excellent empirical case to shed light on the recovery of terrestrial faunas after a mass extinction.

The Permian-Triassic boundary at Meishan, China (Photo: Shuzhong Shen)

The massive volcanic eruptions in Siberia at the end of the Permian, covered more than 2 millions of km 2 with lava flows, releasing more carbon in the atmosphere. High amounts of fluorine and chlorine increased the climatic instability, which means that the Mesozoic began under extreme hothouse conditions. Isotope studies and fossil record, indicates that temperatures in Pangaea interiors during the Early Triassic oscillated between 30 and 40 degrees Celsius, with heat peaks in the Induan and during the Early and Late Olenekian. It was suggested that during that time there was a moderate oxygen depletion that caused the low body size of the amphibian and reptilian life-forms found in those rocks.

After the mass extinction event, a distributed archosauromorph ‘disaster fauna’ dominated by proterosuchids, established for a short time. In South Africa, Proterosuchus occurs only between 5 and 14 m above the PT boundary and a similar pattern has been documented for the synapsid Lystrosaurus. During the Olenekian (1–5 million years after the extinction), archosauromorphs underwent a major phylogenetic diversification with the origins or initial diversification of major clades such as rhynchosaurs, archosaurs, erythrosuchids and tanystropheids.

Stenaulorhynchus stockleyi, a rhynchosaur from the Middle Triassic (From Wikimedia Commons)

The Mid Triassic is marked by the return of conifer-dominated forests, and the end of an interval of intense carbon perturbations, suggesting the recovery and stabilization of global ecosystems. The Anisian (5–10 Myr after the extinction) is characterized by a high diversity among the archosauromorphs with the appearance of large hypercarnivores, bizarre and highly specialized herbivores, long-necked marine predators, and gracile and agile dinosauromorphs. This phylogenetic diversity of archosauromorphs by the Middle Triassic paved the way for the ongoing diversification of the group (including the origins of dinosaurs, crocodylomorphs, and pterosaurs) in the Late Triassic, and their dominance of terrestrial ecosystems for the next 170 million years.

 

 

References:

Ezcurra MD, Butler RJ. 2018 The rise of the ruling reptiles and ecosystem recovery from the Permo-Triassic mass
extinction. Proc. R. Soc. B 285: 20180361. http://dx.doi.org/10.1098/rspb.2018.0361

Ezcurra MD. (2016) The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms. PeerJ 4:e1778 https://doi.org/10.7717/peerj.1778

Holz, M., Mesozoic paleogeography and paleoclimates – a discussion of the diverse greenhouse and hothouse conditions of an alien world, Journal of South American Earth Sciences (2015), doi: 10.1016/j.jsames.2015.01.001

Terrestrial floras at the Triassic-Jurassic Boundary in Europe.

Proportions of range-through diversities of higher taxonomic categories of microfloral elements over the Middle Triassic–Early Jurassic interval (From Barbacka et al., 2017)

Over the last 3 decades, mass extinction events  have become the subject of increasingly detailed and multidisciplinary investigations. Most of those events are associated with global warming and proximal killers such as marine anoxia. Volcanogenic-atmospheric kill mechanisms include ocean acidification, toxic metal poisoning, acid rain, increased UV-B radiation, volcanic darkness, cooling and photosynthetic shutdown. The mass extinction at the Triassic-Jurassic Boundary (TJB) has been linked to the eruption of the Central Atlantic Magmatic Province (CAMP), a large igneous province emplaced during the initial rifting of Pangea. Another theory is that a huge impact was the trigger of the extinction event. At least two craters impact were reported by the end of the Triassic. The Manicouagan Impact crater in the Côte-Nord region of Québec, Canada was caused by the impact of a 5km diameter asteroid, and it was suggested that could be part of a multiple impact event which also formed the Rochechouart crater in France, Saint Martin crater in Canada, Obolon crater in Ukraine, and the Red Wing crater in USA (Spray et al., 1998).

Photographs of some Rhaetian–Hettangian spores and pollen from the Danish Basin (From Lindström, 2015)

Most mammal-like reptiles and large amphibians disappeared, as well as early dinosaur groups. In the oceans, this event eliminated conodonts and nearly annihilated corals, ammonites, brachiopods and bivalves. In the Southern Hemisphere, the vegetation turnover consisted in the replacement to Alisporites (corystosperm)-dominated assemblage to a Classopollis (cheirolepidiacean)-dominated one. But there was no mass extinction of European terrestrial plants during the TJB. The majority of genera and a high percentage of species still existed in its later stages, and replacement seems to have been local, explainable as a typical reaction to an environmental disturbance. In Greenland, for example, the replacement of Triassic wide-leaved forms with Jurassic narrow-leaved forms was linked to the reaction of plants to increased wildfire. In Sweden, wildfire in the late Rhaetian and early Hettangian caused large-scale burning of conifer forests and ferns, and the appearance of new swampy vegetation. In Austria and the United Kingdom, conifers and seed ferns were replaced by ferns, club mosses and liverworts. In Hungary, there was a high spike of ferns and conifers at the TJB, followed by a sudden decrease in the number of ferns along with an increasing share of swamp-inhabiting conifers.

Although certain taxa/families indeed became extinct by the end of the Triassic (e.g. Peltaspermales), the floral changes across Europe were rather a consequence of local changes in topography.

References:

Maria Barbacka, Grzegorz Pacyna, Ádam T. Kocsis, Agata Jarzynka, Jadwiga Ziaja, Emese Bodor , Changes in terrestrial floras at the TriassicJurassic Boundary in Europe, Palaeogeography, Palaeoclimatology, Palaeoecology (2017), doi: 10.1016/j.palaeo.2017.05.024

S. Lindström, Palynofloral patterns of terrestrial ecosystem change during the end-Triassic event — a review, Geol. Mag., 1–23 (2015) https://doi.org/10.1017/S0016756815000552

Van de Schootbrugge, B., Quan, T.M., Lindström, S., Püttmann, W., Heunisch, C., Pross, J., Fiebig, J., Petschick, R., Röhling, H.-G., Richoz, S., Rosenthal, Y., Falkowski, P. G., 2009. Floral changes across the Triassic/Jurassic boundary linked to flood basalt volcanism. Nat. Geosci. 2, 589–594. doi: 10.1038/NGEO577.

N.R. Bonis, W.M. Kürschner, Vegetation history, diversity patterns, and climate change across the Triassic/Jurassic boundary, Paleobiology, 8 (2) (2012), pp. 240–264 https://doi.org/10.1666/09071.1

A Tale of Two Exctintions.

The permian triassic boundary at Meishan, China (Photo: Shuzhong Shen)

The Permian Triassic boundary at Meishan, China (Photo: Shuzhong Shen)

Extinction is the ultimate fate of all species. The fossil record indicates that more than 95% of all species that ever lived are now extinct. Over the last 3 decades, mass extinction events  have become the subject of increasingly detailed and multidisciplinary investigations. In 1982, Jack Sepkoski and David M. Raup identified five major extinction events in Earth’s history: at the end of the Ordovician period, Late Devonian, End Permian, End Triassic and the End Cretaceous. These five events are know as the Big Five.

The end-Permian extinction is the most severe biotic crisis in the fossil record, with as much as 95% of the marine animal species and a similarly high proportion of terrestrial plants and animals going extinct . This great crisis occurred 252 million years ago (Ma) during an episode of global warming. The End-Triassic Extinction  is probably the least understood of the big five. Most mammal-like reptiles and large amphibians disappeared, as well as early dinosaur groups. In the oceans, this event eliminated conodonts and nearly annihilated corals, ammonites, brachiopods and bivalves. Although it’s almost impossible briefly summarize all the changes in biodiversity associated with both extinction events, we can describe their broad trends.

 

Flow chart summarizing proposed cause-and-effect relationships during the end-Permian extinction (From Bond and Wignall, 2014)

Flow chart summarizing proposed cause-and-effect relationships during the end-Permian extinction (From Bond and Wignall, 2014)

Both extinction events are commonly linked to the emplacement of the large igneous provinces of the Siberian Traps and the Central Atlantic Magmatic Province. Massive volcanic eruptions with lava flows, released large quantities of sulphur dioxide, carbon dioxide, thermogenic methane and large amounts of HF, HCl, halocarbons and toxic aromatics and heavy metals into the atmosphere. Furthermore, volcanism contribute gases to the atmosphere, such as Cl, F, and CH3Cl from coal combustion, that suppress ozone formation. Acid rain likely had an impact on freshwater ecosystems and may have triggered forest dieback. Mutagenesis observed in the Lower Triassic herbaceous lycopsid Isoetales has been attributed to increased levels of UV-radiation. Charcoal records point to forest fires as a common denominator during both events. Forest dieback was accompanied by the proliferation of opportunists and pioneers, including ferns and fern allies. Moreover, both events led to major schisms in the dominant terrestrial herbivores  and apex predators, including the late Permian extinction of the pariaeosaurs and many dicynodonts and the end-Triassic loss of crurotarsans (van de Schootbrugge and Wignall, 2016).

Aberrant pollen and spores from the end-Triassic extinction interval (scale bars are 20 μm). (a) Ricciisporites tuberculatus from the uppermost Rhaetian deposits at Northern Ireland (adapted from van de Schootbrugge and Wignall, 2016)

Aberrant pollen and spores from the end-Triassic extinction interval (scale bars are 20 μm). (a) Ricciisporites
tuberculatus and b) Kraeuselisporites reissingerii (adapted from van de Schootbrugge and Wignall, 2016)

During the end-Permian Event, the woody gymnosperm vegetation (cordaitaleans and glossopterids) were replaced by spore-producing plants (mainly lycophytes) before the typical Mesozoic woody vegetation evolved. The palynological record suggests that wooded terrestrial ecosystems took four to five million years to reform stable ecosystems, while spore-producing lycopsids had an important ecological role in the post-extinction interval. A key factor for plant resilience is the time-scale: if the duration of the ecological disruption did not exceed that of the viability of seeds and spores, those plant taxa have the potential to recover (Traverse, 1988). Palynological records from across Europe provide evidence for complete loss of tree-bearing vegetation reflected in a strong decline in pollen abundance at the end of the Triassic. In the Southern Hemisphere, the vegetation turnover consisted in the replacement to Alisporites (corystosperm)-dominated assemblage to a Classopollis (cheirolepidiacean)-dominated one.

Comparison of extinction rates for calcareous organisms during the end-Permian and end-Triassic extinction event (from van de Schootbrugge and Wignall, 2016)

Comparison of extinction rates for calcareous organisms during the end-Permian and end-Triassic extinction event (from van de Schootbrugge and Wignall, 2016)

Rapid additions of carbon dioxide during extreme events may have driven surface waters to undersaturation. 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 foraminifera, planktonic coccolithophores, pteropods and other molluscs,  echinoderms, corals, and coralline algae. Both extinction events led to near-annihilation of cnidarian clades and other taxa responsible for reef construction, resulting in ‘reef gaps’ that lasted millions of years. Black shales deposited across both extinction events also contain increased concentrations of the biomarker isorenieratane, a pigment from green sulphur bacteria, suggesting that the photic zone underwent prolonged periods of high concentrations of hydrogen sulphide. Following the end-Triassic extinction, Early Jurassic shallow seas witnessed recurrent euxinia over a time span of 25 million years, culminating in the Toarcian Oceanic Anoxic Event.

 

References:

BAS VAN DE SCHOOTBRUGGE and PAUL B. WIGNALL (2016). A tale of two extinctions: converging end-Permian and end-Triassic scenarios. Geological Magazine, 153, pp 332-354. doi:10.1017/S0016756815000643.

BACHAN, A. & PAYNE, J. L. 2015. Modelling the impact of pulsed CAMP volcanism on pCO2 and δ13C across the Triassic-Jurassic transition. Geological Magazine, published online

Retallack, G.J. 2013. Permian and Triassic greenhouse crises. Gondwana Research 24:90–103.

 

Unlocking the secrets of the Crater of Doom.

Luis and Walter Alvarez at the K-T Boundary in Gubbio, Italy, 1981 (From Wikimedia Commons)

Luis and Walter Alvarez at the K-T Boundary in Gubbio, Italy, 1981 (From Wikimedia Commons)

The noble and ancient city of Gubbio laid out along the ridges of Mount Ingino in Umbria, was founded by Etruscans between the second and first centuries B.C. The city has an exceptional artistic and monumental heritage which includes marvelous examples of Gothic architecture, like the Palazzo dei Consoli and the Palazzo del Bargello. The rich history of the city is recorded in those buildings. Outside the city, there are exposures of pelagic sedimentary rocks that recorded more than 50 million years of Earth’s history. In the 1970s it was recognized that these pelagic limestones carry a record of the reversals of the magnetic field. The  K-Pg boundary occurs within a portion of the sequence formed by pink limestone containing a variable amount of clay. This limestone, know as the “Scaglia rossa”, is composed by calcareous nannofossils and planktonic foraminifera.

In 1977, Walter Alvarez – an associate professor of geology University of California, Berkeley – was collecting samples of the limestone rock for a paleomagnetism study. He found that the foraminifera from the Upper Cretaceous (notably the genus Globotruncana) disappear abruptly and are replaced by Tertiary foraminifera. The extinction of most of the nannoplankton was simultaneus with the disappearance of the foraminifera (Alvarez et al., 1980).

Forams from the Upper Cretaceous vs. the post-impact foraminifera from the Paleogene. (Images from the Smithsonian Museum of Natural History)

Forams from the Upper Cretaceous vs. the post-impact foraminifera from the Paleogene. (Images from the Smithsonian Museum of Natural History)

At Caravaca on the southeast coast of Spain, Jan Smith, a Dutch geologist, had noticed a similar pattern of changes in forams in rocks around the K-T boundary. Looking for clues, Smith contacted to Jan Hertogen who found high iridium values at the clay boundary. At the same time, Walter Alvarez  gave his father, Luis Alvarez – an American physicist who won the  Nobel Prize in Physics in 1968 – a small polished cross-section of Gubbio  K-Pg boundary rock. The Alvarez gave some samples to Frank Asaro and Helen Michel, who had developed a new technique called neutron activation analysis (NAA). They also discovered the same iridium anomaly. The sea cliff of Stevns Klint, about 50 km south of Copenhagen, shows the same pattern of extinction and iridium anomaly. Another sample from New Zeland also exhibits a spike of iridium. The phenomenon was global.

Iridium is rare in the Earth’s crust but metal meteorites are often rich in iridium. Ten years before the iridium discovery, physicist Wallace Tucker and paleontologist Dale Russell proposed  that a supernova caused the mass extinction at the K-Pg boundary. Luis Alvarez realised that  a supernova would have also released plutonium-244, but there was no plutonium in the sample at all. They concluded that the anomalous iridium concentration at the K-Pg boundary is best interpreted as the result of an asteroid impact, which would explain the iridium and the lack of plutonium. In 1980, they published their seminal paper on Science, along with Asaro and Michel, and ignited a huge controversy. 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).

A paleogeographic map of the Gulf of Mexico at the end of the Cretaceous (From Vellekoop, 2014)

A paleogeographic map of the Gulf of Mexico at the end of the Cretaceous (From Vellekoop, 2014)

In 1981, Pemex (a Mexican oil company) identified Chicxulub as the site of a massive asteroid impact. In 1991, Alan Hildebrand, William Boynton, Glen Penfield and Antonio Camargo, published a paper entitled “Chicxulub crater: a possible Cretaceous/Tertiary boundary impact crater on the Yucatan Peninsula, Mexico.” They had found the long-sought K/Pg impact crater.

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  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. Model simulations suggest that the amount of sunlight that reached Earth’s surface was reduced by approximately 20%.This decrease of sunlight caused a drastic short-term global reduction in temperature. This phenomenon is called “impact winter”. Cold and darkness lasted for a period of months to years.  Photosynthesis stopped and the food chain collapsed. This period of reduced solar radiation may only have lasted several months to decades. 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. Additionally, the vapour produced by the impact  could have led to global acid rain and a dramatic acidification of marine surface waters.

The Chicxulub asteroid impact was the final straw that pushed Earth past the tipping point.  The K-Pg extinction that followed the impact was one of the five great Phanerozoic  mass extinctions. Currently about 170 impact craters are known on Earth; about one third of those structures are not exposed on the surface and can only be studied by geophysics or drilling. Now, a new drilling platform in the the Gulf of Mexico, sponsored by the International Ocean Discovery Program (IODP) and the International Continental Scientific Drilling Program, will looking rock cores from the site of the impact. The main object is learn more about the scale of the impact, and the environmental catastrophe that ensued.

References:

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.

Alvarez, W. (1997) T. rex and the Crater of Doom. Princeton University Press, Princeton, NJ.

Hildebrand, A.R., G.T. Penfield, D.A. Kring, M. Pilkington, A. Camargo, S.B. Jacobsen, and W.V. Boynton. 1991. Chicxulub crater: A possible Cretaceous/Tertiary boundary impact crater on the Yucatán Peninsula, Mexico. Geology 19:867–71.

 

 

A Brief Introduction to The Hell Creek Formation.

Hell Creek e Fort Union contact, as seen at Mountain Goat Lake Butte, southwestern North Dakota (Adapted from Fastovsky and Bercovici, 2015)

Hell Creek- Fort Union contact, as seen at Mountain Goat Lake Butte, southwestern North Dakota (Adapted from Fastovsky and Bercovici, 2015)

The Hell Creek Formation (HCF), in the northern Great Plains of the United States, is the most studied source for understanding the changes in the terrestrial biota across the Cretaceous-Paleogene boundary, because preserves an extraordinary record comprised of fossil flora, vertebrates, invertebrates, microfossils, a range of trace fossils, and critical geochemical markers such as multiple iridium anomalies associated with the Chicxulub impact event. The HCF is a fine-grained, fluvially derived, siliciclastic unit, that occupies part of the western Williston Basin, and overlies the Fox Hills Formation (Clemens and Hartman, 2014).
The history of research focused on the Hell Creek Formation and its biota started in October 1901, when William T. Hornaday, director of the New York Zoological Society, travelled to northeastern Montana and discovered three fragments of the nasal horn of a Triceratops in the valley of Hell Creek. He showed the fossils to Henry Fairfield Osborn who decided to include the valley of Hell Creek on the list of areas to be prospected by Barnum Brown the following year.
braun

Barnum Brown working in a quarry in 1902.

In July 1902, B. Brown arrived to Hell Creek. His field crew included Dr. Richard Swann Lull, and Phillip Brooks. Brown recounted that after their arrival, he found the partial skeleton that would become the type specimen of Tyrannosaurus rex. In 1904, William H. Utterback, preparator and collector for the Carnegie Museum of Natural History, collected a fragment of a jaw of Tyrannosaurus and two skulls of Triceratops. In the summer of 1906, B. Brown returned to Montana, and a year later he published a complete manuscript about the valley of Hell Creek. The field expeditions of 1908 and 1909 were crowned by the discovery of another skeleton of T-rex. Between 1902 and 1910, Osborn, Brown, and Lull published the analysis of some of the fossil vertebrates discovered in the Hell Creek Formation, including Tyrannosaurus rex, Triceratops, and Ankylosaurus.
Micrograph of Wodehouseia spinata and a specimenBisonia niemi, from the upper part of the Hell Creek Formation (Adapted from Fastovsky and Bercovici, 2015).

Micrograph of Wodehouseia spinata and a specimen Bisonia niemi, from the upper part of the Hell Creek Formation (Adapted from Fastovsky and Bercovici, 2015).

Plants are represented by fossil leaves, seeds and cones. Fossil wood is also commonly found in the HCF as permineralized fragments. The Hell Creek macroflora is largely dominated by angiosperms including palms, associated with several ferns, conifers, and single species of cycads and Ginkgo. The study of pollen and spores has played a very important role in the identification of the K/Pg boundary in the HCF. Palynologists were the first scientists to recognize that a major, abrupt change occurred at the end of the Cretaceous. Unlike the Permian-Triassic and Triassic-Jurassic boundaries, the palynologically defined K/Pg boundary is based on the extinction of Cretaceous taxa rather than the appearance of Paleocene taxa. Intimately associated with the K/Pg boundary globally, is the so-called “fern spike”, occurring exclusively at localities where the iridium anomaly is present. (Fastovsky and Bercovici, 2015; Vajda & Bercovici, 2014.)

 

References:

Fastovsky, D. E., & Bercovici, A., The Hell Creek Formation and its contribution to the CretaceousePaleogene extinction: A short primer, Cretaceous Research (2015), http://dx.doi.org/10.1016/j.cretres.2015.07.007
Clemens, W. A., Jr., & Hartman, J. H. (2014). From Tyrannosaurus rex to asteroid impact: early studies (1901- 1980) of the Hell Creek Formation in its type area. In J. Hartman, K. R. Johnson, & D. J. Nichols (Eds.), Geological society of America special paper: 361. The Hell Creek Formation and the Cretaceous-tertiary boundary in the northern great plains (pp. 217-245).
Husson, D., Galbrun, B., Laskar, J., Hinnov, L. A., Thibault, N., Gardin, S., & Locklair, R. E. (2011). “Astronomical calibration of the Maastrichtian (late Cretaceous)”. Earth and Planetary Science Letters 305 (3): 328–340.doi:10.1016/j.epsl.2011.03.008
Johnson, K. R., Nichols, D. J., & Hartman, J. H. (2002). Hell Creek Formation: A 2001 synthesis. The Hell Creek Formation and the Cretaceous-Tertiary Boundary in the northern Great Plains: Geological Society of America Special Paper, 361, 503-510.

The Middle Permian mass extinction.

The Kapp Starostin Formation, Festningen section, Spitsbergen. The uppermost of the 3 yellow limestone beds records the Middle Permian mass extinction (Credit: Photographer: Dierk Blomeier. For David P.G. Bond and colleagues, GSA Bulletin, 2015.)

The Kapp Starostin Formation, Festningen section, Spitsbergen. The uppermost of the 3 yellow limestone beds records the Middle Permian mass extinction (Photo Credit: Dierk Blomeier. For David P.G. Bond and colleagues, GSA Bulletin, 2015.)

Extinction is the ultimate fate of all species. The fossil record indicates that more than 95% of all species that ever lived are now extinct. Individuals better adapted to environments are more likely to survive and when a species does fail, it is called a background extinction. Occasionally extinction events reach a global scale, with many species of all ecological types dying out in a near geological instant. These are mass extinctions. They were originally identified in the marine fossil record and have been interpreted as a result of catastrophic events or major environmental changes that occurred too rapidly for organisms to adapt.  Mass extinctions are probably due to a set of different possible causes like basaltic super-eruptions, impacts of asteroids, global climate changes, or continental drift.

George Cuvier, the great French anatomist and paleontologist, was the first to suggested that periodic “revolutions” or catastrophes had befallen the Earth and wiped out a number of species. But under the influence of Lyell’s uniformitarianism, Cuvier’s ideas were rejected as “poor science”. The modern study of mass extinction did not begin until the middle of the twentieth century. One of the most popular of that time was “Revolutions in the history of life” written by Norman Newell in 1967.

The fossil record shows that biodiversity in the world has been increasing dramatically for 200 million years and is likely to continue. The two mass extinctions in that period (at 201 million and 66 million years ago) slowed the trend only temporarily. Genera are the next taxonomic level up from species and are easier to detect in fossils. The Phanerozoic is the 540-million-year period in which animal life has proliferated. Chart created by and courtesy of University of Chicago paleontologists J. John Sepkoski, Jr. and David M. Raup.

Biodiversity in the fossil record.  (From Wikimedia Commons)

Over the last 3 decades, mass extinction events  have become the subject of increasingly detailed and multidisciplinary investigations. In 1982, Jack Sepkoski and David M. Raup used a simple form of time series analysis at the rank of family to distinguish between background extinction levels and mass extinctions in marine faunas, and identified five major extinction events in Earth’s history: at the end of the Ordovician period, Late Devonian, End Permian, End Triassic and the End Cretaceous. These five events are know as the Big Five. The most recently identified mass extinction occurred during the Middle Permian, about  262 million years ago, and it was first recognised in the marine realm as a turnover among foraminifera, with fusulinaceans among the principal casualties. The crisis also affected numerous other shallow-marine taxa, including corals, bryozoans, brachiopods, bivalves and ammonoids. Until now, all detailed studies have focused on equatorial sections, especially those of South China. That extinction coincide with the Emeishan large igneous province. But, new data indicates that at the same time there was two severe extinctions amongst brachiopods in northern boreal latitudes in the Kapp Starostin Formation of Spitsbergen, an island roughly 890 km north of the Norwegian mainland.

Fusulinids from the Topeka Limestone  (Upper Carboniferous of Kansas, USA) From Wikimedia Commons

Fusulinids from the Topeka Limestone (Upper Carboniferous of Kansas, USA) From Wikimedia Commons

The Kapp Starostin Formation contains cool-water boreal faunas that include abundant siliceous sponges, brachiopods, and bryozoans. The widespread and near-total loss of carbonates across the Boreal Realm also suggests a role for acidification in the crisis.  This extinction predates the end-Permian mass extinction, because a subsequent recovery of brachiopods and especially bivalves is seen in the Late Permian. This post-extinction fauna disappears 10 m below the top of the Kapp Starostin Formation and thus fails to survive until the end of the Permian (Bond et al., 2015). This is a true mass extinction because the new data suggest that about 50 per cent of all marine species died during the event.

Oceanic oxygen depletion represents a potent cause of extinction in marine settings, and is often linked with volcanic activity, warming, and transgression. However,  the role of anoxia in the wider Capitanian extinction scenario remains enigmatic. Volcanically induced effects are multiple and include acidification.

brachi

Brachiopods from the Kapp Starostin Formation (Image adapted from Bond et al., 2015)

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 foraminifera, planktonic coccolithophores, pteropods and other molluscs,  echinoderms, corals, and coralline algae. 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. But, recently, a variety of trace-element and isotopic tools have become available to infer past seawater carbonate chemistry.

Undoubtedly, the proximity of the End Permian extinction, makes difficult to determine if these events are separate or are part of a the same event.

References:

David P.G. Bond, Paul B. Wignall, Michael M. Joachimski, Yadong Sun, Ivan Savov, Stephen E. Grasby, Benoit Beauchamp and Dierk P.G. Blomeier, 2015, An abrupt extinction in the Middle Permian (Capitanian) of the Boreal Realm (Spitsbergen) and its link to anoxia and acidification, Geological Society of America Bulletin, doi: 10.1130/B31216.1

Wignall, P.B., Bond, D.P.G., Kuwahara, K., Kakuwa, Y., Newton, R.J., and Poulton, S.W., 2010, An 80 million year oceanic redox history from Permian to Jurassic pelagic sediments of the Mino-Tamba terrane, SW Japan, and the origin of four mass extinctions: Global and Planetary Change, v. 71, p. 109–123, doi:10.1016/j.gloplacha .2010.01.022.

Wignall, P.B., Bond, D.P.G., Newton, R.J., Haas, J., Hips, K., Wang, W., Jiang, H.-S., Lai, X.-L., Sun, Y.-D., Altiner, D., Védrine, S., and Zajzon, N., 2012, The Capitanian (Middle Permian) mass extinction in western Tethys: A fossil, facies and δ13C study from Hungary and Hydra Island (Greece): Palaios, v. 27, p. 78–89, doi:10.2110/palo.2011.p11-058r.

Ocean acidification and the end-Permian mass extinction

 

Permian Seafloor Photograph by University of Michigan Exhibit Museum of Natural History.

Permian Seafloor
Photograph by University of Michigan Exhibit Museum of Natural History.

About one third of the carbon dioxide released by anthropogenic activity is absorbed by the oceans. But the CO2 uptake lowers the pH and alters the chemical balance of the oceans. This phenomenon is called ocean acidification, and is occurring at a rate faster than at any time in the last 300 million years (Gillings, 2014; Hönisch et al. 2012). 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, pteropods and other molluscs,  echinoderms, corals, and coralline algae. Rapid additions of carbon dioxide during extreme events in Earth history, including the end-Permian mass extinction (252 million years ago) and the Paleocene-Eocene Thermal Maximum (PETM, 56 million years ago) may have driven surface waters to undersaturation.

Flow chart summarizing proposed cause-and-effect relationships during the end-Permian extinction (From Bond and Wignall, 2014)

Flow chart summarizing proposed cause-and-effect relationships during the end-Permian extinction (From Bond and Wignall, 2014)

The end-Permian extinction is the most severe biotic crisis in the fossil record, with as much as 95% of the marine animal species and a similarly high proportion of terrestrial plants and animals going extinct . This great crisis occurred about 252 million years ago (Ma) during an episode of global warming.  The cause or causes of the Permian extinction remain a mystery but new data indicates that the extinction had a duration of 60,000 years and may be linked to massive volcanic eruptions from the Siberian Traps. The same study found evidence that 10,000 years before the die-off, the ocean experienced a pulse of light carbon that most likely led to a spike of carbon dioxide in the atmosphere. Volcanism and coal burning also contribute gases to the atmosphere, such as Cl, F, and CH3Cl from coal combustion, that suppress ozone formation.

Image that shows field work in the United Arab Emirates. Credit: D. Astratti

Image that shows field work in the United Arab Emirates. Credit: D. Astratti

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. But, recently, a variety of trace-element and isotopic tools have become available to infer past seawater carbonate chemistry. The boron isotope composition of carbonate samples obtained from a shallow-marine platform section at Wadi Bih on the Musandam Peninsula, United Arab Emirates, allowed to reconstruct seawater pH values and atmospheric pCO2 concentrations and obtain for the very first time, direct evidence of ocean acidification in the Permo-Triassic boundary. The evidence indicates that the first phase of extinction was coincident with a slow injection of carbon into the atmosphere, and ocean pH remained stable. During the second extinction pulse, however, a rapid and large injection of carbon caused an abrupt acidification event that drove the preferential loss of heavily calcified marine biota (Clarkson et al, 2015).

The increasing evidence that the end-Permian mass extinction was precipitated by rapid release of CO2 into Earth’s atmosphere is a valuable reminder for an immediate action on global carbon emission reductions.

 

References:

Clarkson MO, Kasemann SA, Wood RA, Lenton TM, Daines SJ, Richoz S, Ohnemueller F, Meixner A, Poulton SW, Tipper ET. Ocean acidification and the Permo-Triassic mass extinction. Science, 2015 DOI: 10.1126/science.aaa0193

Feng, Q., Algeo, T.J., Evolution of oceanic redox conditions during the Permo-Triassic transition: Evidence from deepwater radiolarian facies, Earth-Sci. Rev. (2014), http://dx.doi.org/10.1016/j.earscirev.2013.12.003

Hönisch, A. Ridgwell, D. N. Schmidt, E. Thomas, S. J. Gibbs, A. Sluijs, R. Zeebe, L. Kump, R. C. Martindale, S. E. Greene, W. Kiessling, J. Ries, J. C. Zachos, D. L. Royer, S. Barker, T. M. Marchitto Jr., R. Moyer, C. Pelejero, P. Ziveri, G. L. Foster, B. Williams, The geological record of ocean acidification. Science 335, 1058–1063 (2012).

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

Seth D. Burgess, Samuel Bowring, and Shu-zhong Shen, High-precision timeline for Earth’s most severe extinction, PNAS 2014, doi:10.1073/pnas.1317692111