The end-Triassic extinction: A tale of Death and Global Warming.

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

For the last 540 million years, five mass extinction events shaped the history of the Earth. The End-Triassic Extinction (ETE) is typically attributed to climate change associated with degassing of basalt flows from the central Atlantic magmatic province (CAMP) emplaced during the initial rifting of Pangea. 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.

The emplacement of CAMP started c. 100,000 years before the end-Triassic event and continued in pulses for 700,000 years. Three negative organic C-isotope excursions (CIEs) have being recognized at the end-Triassic: the Marshi, the Spelae, and the top-Tilmanni CIEs. A recent study published in Nature estimated that a single short-lived magmatic pulse would have released about 5 × 1016 mol CO2, roughly the same total amount of projected anthropogenic emissions over the 21st century, causing an increase of about 2 °C in global temperatures, and an oceanic pH decrease of about 0.15 units over 0.1 kyrs, suggesting that the end-Triassic climatic and environmental changes, driven by CO2 emissions, may have been similar to those predicted for the near future.

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

These massive volcanic eruptions with lava flows, also released large quantities of sulphur dioxide, thermogenic methane and large amounts of HF, HCl, halocarbons and toxic aromatics and heavy metals into the atmosphere, resulting in global warming, and ozone layer depletion. The high concentrations of pCO2 are indicative of ocean acidification suggesting that this may have been a marine extinction mechanism especially in relation to the scleractinian corals. Mutagenesis observed in plants and their reproductive cells (spores and pollen) were likely caused by mercury, the most genotoxic element on Earth .

The new study confirms the abundance of CO2 (up to 105 Gt volcanic CO2 degassed during CAMP emplacement) and indicates that at least part of this carbon has a middle- to lower-crust or mantle origin, suggesting that CAMP eruptions were rapid and potentially catastrophic for both climate and biosphere. Since the industrial revolution, the wave of animal and plant extinctions that began with the late Quaternary has accelerated. Australia has lost almost 40 percent of its forests, and almost 20% of the Amazon has disappeared in last five decades.Calculations suggest that the current rates of extinction are 100–1000 times above normal, or background levels. If we want to stop the degradation of our planet, we need to act now.

 

References:

Capriolo, M., Marzoli, A., Aradi, L.E. et al. Deep CO2 in the end-Triassic Central Atlantic Magmatic Province. Nat Commun 11, 1670 (2020). https://doi.org/10.1038/s41467-020-15325-6

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}

Davies, J., Marzoli, A., Bertrand, H. et al. End-Triassic mass extinction started by intrusive CAMP activity. Nat Commun 8, 15596 (2017). https://doi.org/10.1038/ncomms15596

A Short History of the Early Female Geoscientists from Argentina

Mathilde Dolgopol de Saez. Image credit: Asociación Paleontológica Argentina (A.P.A.)

Women have played various and extensive roles in the history of geology. Unfortunately, their contribution has not been widely recognised by the public or academic researchers. In the 18th and 19th centuries women’s access to science was limited, and science was usually a ‘hobby’ for intelligent wealthy women. Early female scientists were often born into influential families, like Grace Milne, the eldest child of Louis Falconer and sister of the eminent botanist and palaeontologist, Hugh Falconer; or Mary Lyell, the daughter of the geologist Leonard Horner. They collected fossils and mineral specimens, and were allowed to attend scientific lectures, but they were barred from membership in scientific societies. Thanks to the pioneer work of these women, the 20th century saw the slow but firm advance of women from the periphery of science towards the center of it.

Edelmira Inés Mórtola (1894-1973)

In Argentina, during the 1870s, public schools were organized and expanded for the training of teachers in different cities of the country. North American teachers were hired, some of whom promoted among their students the interest in pursuing university studies. Cecilia Grierson (1859-1934) was the first woman to earn a PhD in Medicine and Surgery in 1889. She was an important reference for other women, collaborating in the women’s movement in the early twentieth century.

The first papers in natural sciences signed by women were published around 1910. Edelmira Inés Mórtola was the first woman to earn her Ph. D in geology in Argentina, in 1921. She was also the first woman to work for the Dirección General de Minas, Geología, e Hidrología (DGMGH) in 1919. She focus on teaching and was an inspiring figure for young women. In 1924, she was appointed Professor at the Universidad de Buenos Aires (UBA). The Museum of Mineralogy “Dr. E. Mórtola “, that she helped to organize, honors her extraordinary career. She died on May 28, 1973.

Noemí Violeta Cattoi. Image credit: Asociación Paleontológica Argentina (A.P.A.)

Mathilde Dolgopol de Saez was born on March 6, 1901. She was one of the first female paleontologist from Argentina (graduated in 1927), along with Ana Cortelezzi (1928?), Dolores López Aranguren (1930), Andreína Bocchino de Ringuelet (1930?) y Enriqueta Vinacci Thul (1930). Unfortunately, only her thesis and the one of López Aranguren were formally published. The mayor part of her research was focused on fossil fish and birds. She died on June 27, 1957.

Noemí Violeta Cattoi was born in Buenos Aires on December 23, 1911. She received her PhD degree in Natural Science at the University of Buenos Aires, but before her graduation she was trained at the Museo Argentino de Ciencias Naturales. She was head of Paleozoology at the Museum, and adjunt professor at the Museo de la Plata. Her research was mainly focused on extinct birds and mammals from South America. She was also one of the founding member of the Asociación Paleontológica Argentina (A.P.A), along with María Bonetti de Stipanicic, Andreína B. de Ringuelet, Elsa F. de Alvarez and Hildebranda A. Castellaro. Noemí Cattoi died on January 29, 1965.

Reference:.

Rafael Herbst, Luisa M. Anzótegui, Las mujeres en la paleontología argentina, Revista del Museo de La Plata (2016) Volumen 1, Número Especial: 130-13 DOI:https://doi.org/10.24215/25456377e024

GARCIA, Susana V.. Ni solas ni resignadas: la participación femenina en las actividades científico-académicas de la Argentina en los inicios del siglo XX. Cad. Pagu [online]. 2006, n.27, pp.133-172 https://doi.org/10.1590/S0104-83332006000200007.

Link: https://www.apaleontologica.org.ar/

“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

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

Christmas edition: Geologizing with Dickens, part II.

dickens_by_watkins_1858

Charles Dickens at his desk, by George Herbert Watkins (National Portrait Gallery. From Wikimedia Commons)

Charles Dickens (1812- 1870) revitalized the traditions of Christmas, and to Victorian England, Dickens was Christmas. He had only 31, when began to write A Christmas Carol. The novella tells the story of  Ebenezer Scrooge, a bitter old man who finds salvation through the visits of the three Ghosts of Christmas (Ghost of Christmas Past, Ghost of Christmas Present, and Ghost of Christmas Yet to Come). But Dickens also contributed to the popularity of geology in the nineteenth century. Among his friends were Richard Owen and Sir Roderick Murchison. For Dickens, the ideal science is Geology. In his review of Hunt’s Poetry of Science, he wrote: “Science has gone down into the mines and coal-pits, and before the safety-lamp the Gnomes and Genii of those dark regions have disappeared … Sirens, mermaids, shining cities glittering at the bottom of quiet seas and in deep lakes, exist no longer; but in their place, Science, their destroyer, shows us whole coasts of coral reef constructed by the labours of minute creatures; points to our own chalk cliffs and limestone rocks as made of the dust of myriads of generations of infinitesimal beings that have passed away; reduces the very element of water into its constituent airs, and re-creates it at her pleasure…” (London Examiner, 1848).

In 1846, Dickens visited Naples and climbed the Mount Vesuvius. He described that experience in Pictures from Italy. He wrote: “Stand at the bottom of the great market-place of Pompeii, and look up the silent streets, through the ruined temples of Jupiter and Isis, over the broken houses with their inmost sanctuaries open to the day, away to Mount Vesuvius, bright and snowy in the peaceful distance; and lose all count of time, and heed of other things, in the strange and melancholy sensation of seeing the Destroyed and the Destroyer making this quiet picture in the sun.”

An eruption of Vesuvius circa 1845. Credit: Enrico La Pira.

An eruption of Vesuvius circa 1845. Credit: Enrico La Pira.

Mount Vesuvius is a stratovolcano, consisting of an external truncated cone, the extinct Mt. Somma,  a smaller cone represented by Vesuvius. For this reason, the volcano is also called Somma-Vesuvio. It was formed by the collision of two tectonic plates, the African and the Eurasian. When Mount Vesuvius erupted in 79 AD released deadly cloud of ash and molten rocks, and lasted eight days, burying and destroying the cities of Pompeya, Herculaneum and Stabiae. Vesuvius has the world’s oldest volcano observatory, established in 1845, and Dickens’s own magazine Household Words, frequently ran travel pieces describing the ascent and descent of Vesuvius, alongside trips to Pompei.

The same year, Dickens began to to write Dombey and Son, using his experiences in Italy to describe a violent eruption: “Hot springs and fiery eruptions, the usual attendants upon earthquakes, lent their contributions of confusion to the scene. Boiling water hissed and heaved within dilapidated walls; whence, also, the glare and roar of flames came issuing forth; and mounds of ashes blocked up rights of way, and wholly changed the law and custom of the neighbourhood”. 

Benjamin Waterhouse Hawkins unveiled the first ever sculptures of Iguanodons.

Benjamin Waterhouse Hawkins unveiled the first ever sculptures of Iguanodons.

It was an exciting time full of discoveries and the concept of an ancient Earth became part of the public understanding. The study of the Earth was central to the economic and cultural life of the Victorian Society and Literature influenced the pervasiveness of geological thinking. So when the Crystal Palace was reconstructed at Sydenham in 1854, Dickens and his Household Words were very enthusiastic. Megalosaurus became so popular that is mentioned in his novel Bleak House. In this novel the dinosaurs uncovered by the railway in Dombey and Son move centre stage: “Implacable November weather. As much mud in the streets as if the waters had but newly retired from the face of the earth, and it would not be wonderful to meet a Megalosaurus, forty feet long or so, waddling like an elephantine lizard up Holborn Hill.”  

In Bleak House and Dombey and Son, Dickens encourage reader to perceive the scene of the city as a geological fragment of a much broader spatial and temporal vision. In his last novel Our Mutual Friend (1864–65), Mr Venus, the taxidermist was slightly based on Richard Owen. By the time when Dickens wrote this novel, Owen was the curator of the Hunterian Museum of the Royal College of Surgeons. Our Mutual Friend, also exhibits  traces of the work of Lyell, Jean-Baptiste Lamarck, and Darwin.

References:

A. BUCKLAND, ‘“The Poetry of Science”: Charles Dickens, Geology and Visual and Material Culture in Victorian London’, Victorian Literature and Culture, 35 (2007), 679–94 (p. 680).

A. BUCKLAND. Novel Science: Fiction and the Invention of Nineteenth-Century Geology. Chicago, IL and London: University of Chicago Press, 2013. 400 pp. 9 plts. $45.00. ISBN 978-0-226-07968-4

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.

 

 

Application of diatoms to tsunami studies.

Lisbon earthquake and tsunami in 1755 (From Wikipedia Commons)

Lisbon earthquake and tsunami in 1755 (From Wikipedia Commons)

Diatoms are unicellular algae with golden-brown photosynthetic pigments with a fossil record that extends back to Early Jurassic. The most distinctive feature of diatoms is their siliceous skeleton known as frustule that comprise two valves. They live in aquatic environments, soils, ice, attached to trees or anywhere with humidity and their remains accumulates forming diatomite, a type of soft sedimentary rock. Diatoms are the dominant marine primary producers in the oceans and play a key role in the carbon cycle and in the removal of biogenic silica from surface waters. But diatoms are also a valuable tool in reconstructing paleoenvironmental changes because of their sensitivity to environmental factors including salinity, tidal exposure, substrate, vegetation, pH, nutrient supply, and temperature found in specific coastal wetland environments. Through years, diatoms become part of the coastal sediments, resulting in buried assemblages that represent an environmental history that can span thousands of years. Diatoms alone cannot differentiate tsunami deposits from other kinds of coastal deposits, but they can provide valuable evidence for the validity of proposed tsunami deposits (Dura et al., 2015).

Electron microscope image of Diatoms from high altitude aquatic environments of Catamarca Province, Argentina (From Maidana and Seeligmann, 2006)

Electron microscope image of Diatoms from high altitude aquatic environments of Catamarca Province, Argentina (From Maidana and Seeligmann, 2006)

Tsunami deposits can be identify by finding anomalous sand deposits in low-energy environments such as coastal ponds, lakes, and marshes. Those anomalous deposits are diagnosed using several criteria such as floral (e.g. diatoms) and faunal fossils within the deposits. The delicate valves of numerous diatom species may be unusually well preserved when removed from surface deposits and rapidly buried by a tsunami.

Diatoms within the tsunami deposits are generally composed of mixed assemblages, because tsunamis inundated coastal and inland areas, eroding, transporting, and depositing brackish and freshwater taxa. Nonetheless, problems differentiating autochthonous (in situ) and allochthonous (transported) diatoms complicates reconstructions. In general, planktonic diatoms are considered allochthonous components in modern and fossil coastal wetland assemblages, while benthic taxa can be considered as autochthonous. Diatoms can also be used to estimate tsunami run-up  by mapping the landward limit of diatom taxa transported by the tsunami.

 

References:

Hemphill-Haley, E., 1996. Diatoms as an aid in identifying late Holocene tsunami deposits. The Holocene 6, 439–448.

Tina Dura, Eileen Hemphill-Haley, Yuki Sawai, Benjamin P. Horton, The application of diatoms to reconstruct the history of subduction zone earthquakes and tsunamis, Earth-Science Reviews 152 (2016) 181–197. DOI: 10.1016/j.earscirev.2015.11.017

Armstrong, H. A., Brasier, M. D., 2005. Microfossils (2nd Ed). Blackwell, Oxford.

Barron, J.A. (2003). Appearance and extinction of planktonic diatoms during the past 18 m.y. in the Pacific and Southern oceans. “Diatom Research” 18, 203-224

The geological observations of Robert Hooke.

Ammonite fossil illustrations drawn by Robert Hooke (‘Discourse on Earthquakes’ from 1703).

Ammonite fossil illustrations drawn by Robert Hooke (‘Discourse on Earthquakes’ from 1703).

At the beginning of the sixteenth century and throughout the seventeenth century a great debate about the true nature of fossils started in Italy and extended to Europe. There was two hypothesis in dispute: the first one postulated an inorganic origin for the fossils (directly formed within rocks) and the second, which contemplated an organic origin. The court doctor to the Grand Duke of Tuscany, Nicola Steno argued that the stones called Glossopetrae or “tongue stones” looked like shark teeth because they were shark teeth deposited a long time ago. In 1667, Henry Oldenburg, the secretary of the Royal Society included an abstract of ‘The head of a shark dissected’ (Canis Carchariae Dissectum Caput) by Nicolas Steno in one of the early issues of the Philosophical Transactions. Robert Hooke (1635-1703), Curator of Experiments of the Royal Society, expressed similar ideas two years before Steno. In ‘Micrographia’ (1665) he  argued that the micro-structure of petrified wood were identical to those seen in normal wood. He also described the ‘serpentine stones’ and concluded that these stones were not formed due any ‘plastic virtue’, but were due to shells of shellfish that became filled with mud or clay or petrifying water and had over time rotted away, leaving their impressions ‘both on the containing and contained substances’ (Kusukawa, 2013).

Between 1667 and 1700, Hooke delivered a series of at least 27 lectures or ‘Discourses’ to the Royal Society on the generic subject of ‘Earthquakes’, or earth-forming processes, published in his Posthumous works (1705), and accompanied by some of Hooke’s drawings that survived among the papers of Sir Hans Sloane.

Hooke's drawing of fossil bivalves, brachiopods, belemnites, shark teeth and possibly a reptilian tooth (Copyright © The Royal Society)

Hooke’s drawing of fossil bivalves, brachiopods, belemnites, shark teeth and possibly a reptilian tooth (Copyright © The Royal Society)

Hooke’s ‘wandering poles’ theory was the first dynamic explanation of continent formation in the history of science. ‘The Earth’s rotation, he proposed, caused a bulge and thus greater altitude at the equator versus a flattening at the poles. He maintained that over time, a change in the positions of the poles on the Earth surface due to a change in the moment of inertia would cause different areas of bulging and flattening with the creation of new land or sea areas’ (Drake, 2007).

By the time that he delivered his third series of ‘Discourses’ in 1687, Hooke had arrived to three remarkable conclusions. First, that fossils were the petrified remains of once living creatures (he called ‘medals of Nature’ and part of ‘Nature’s Grammar’, to be collected like coins and read like texts) and not just twists in the rock. Second, that there had been radical changes of sea level. Third, that hill-tops in England had once formed the beds of tropical oceans as indicated by the discovered of gigantic sea shells.

Hooke’s writings were intimately connected to his birthplace: the town of Freshwater near the western edge of the Isle of Wight. Throughout his Discourses he mentioned the cliffs around Freshwater Bay from which he collected fossils. Unfortunately, many of the fossils that he collected for the Royal Society, along with his portrait as Secretary of the Society, many papers and several scientific instruments and models designed by Hooke are lost, but Hooke’s ideas were transmitted by later writers, demonstrating the continuity of the development of geological thought. Arthur Percival Rossiter even nominated him in 1935 as ‘The First English Geologist’.

Reference:

E. T. Drake, The geological observations of Robert Hooke (1635-1703) on the Isle of Wight; p19-30. Geological Society, London, Special Publications 2007, v.287; doi: 10.1144/SP287.3

Sachiko Kusukawa, Drawings of fossils by Robert Hooke and Richard Waller, Notes Rec. R. Soc. 2013 67 123-138; DOI: 10.1098/rsnr.2013.0013. Published 3 April 2013

M. J. S. Rudwick, The meaning of fossils: episodes in the history of palaeontology(University of Chicago Press, 1985)

 

The Great Acceleration.

 

Iron and Coal, 1855–60, by William Bell Scott illustrates the central place of coal and iron working in the industrial revolution (From Wikimedia Commons)

Iron and Coal, 1855–60, by William Bell Scott illustrates the central place of coal and iron working in the industrial revolution (From Wikimedia Commons)

During a meeting of the International Geosphere-Biosphere Programme (IGBP) celebrated in Mexico, in 2000, the Vice-Chair of IGBP, Paul Crutzen, proposed the use of the term Anthropocene to designate the last three centuries of human domination of earth’s ecosystems, and to mark the end of the current Holocene geological epoch. He suggested that the start date of the Anthropocene must be placed near the end of the 18th century, about the time that the industrial revolution began, and noted that such a start date would coincide with the invention of the steam engine by James Watt in 1784.

Although there is no agreement on when the Anthropocene started, researchers accept that the Anthropocene is a time span marked by human interaction with Earth’s biophysical system. It has been defined, primarily, by significant and measurable increases in anthropogenic greenhouse gas emissions from ice cores, and other geologic features including synthetic organic compounds and radionuclides. Eugene Stoermer, in an interview in 2012, proposed that the geological mark for the Anthropocene was the isotopic signature of the first atomic bomb tests. Hence,  Anthropocene deposits would be those that may include the globally distributed primary artificial radionuclide signal (Zalasiewicz et al, 2015).

 

anthropocene

Alternative temporal boundaries for the Holocene–Anthropocene boundary (calibrated in thousand of years before present) From Smith 2013

 

Human activity is a major driver of the dynamics of Earth system. After the World War II, the impact of human activity on the global environment dramatically increased. This period associated with very rapid growth in human population, resource consumption, energy use and pollution, has been called the Great Acceleration.

During the Great Acceleration, the atmospheric CO2 concentration grew, from 311 ppm in 1950 to 369 ppm in 2000 (W. Steffen et al., 2011). About one third of the carbon dioxide released by anthropogenic activity is absorbed by the oceans. When CO2 dissolves in seawater, it produce carbonic acid. The carbonic acid dissociates in the water releasing hydrogen ions and bicarbonate. Then, the formation of bicarbonate removes carbonate ions from the water, making them less available for use by organisms. Ocean acidification affects the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus in the ocean, and will directly impact in a wide range of marine organisms that build shells from calcium carbonate, like planktonic coccolithophores, molluscs,  echinoderms, corals, and coralline algae.

Clastic plastiglomerate containing molten plastic and basalt and coral fragments (Image adapted from P. Corcoran et al., 2014)

Clastic plastiglomerate containing molten plastic and basalt and coral fragments (Image adapted from P. Corcoran et al., 2013)

One important marker for the future geological record is a new type of rock formed by anthropogenically derived materials. This type of rock has been named plastiglomerate, and has been originally described on Kamilo Beach, Hawaii. This anthropogenically influenced material has great potential to form a marker horizon of human pollution, signaling the occurrence of the Anthropocene epoch (Corcoran et al., 2013).

Climate change, shifts in oceanic pH, loss of biodiversity and widespread pollution have all been identified as potential planetary tipping point. Since the industrial revolution, the wave of animal and plant extinctions that began with the late Quaternary has accelerated. Calculations suggest that the current rates of extinction are 100–1000 times above normal, or background levels. We are in the midst of  the so called “Sixth Mass Extinction”.

Dealing with the transition into the Anthropocene requires careful consideration of its social, economic and biotic effects. In his master book L’Evolution Créatrice (1907), French philosopher Henri Bergson, wrote:  “A century has elapsed since the invention of the steam engine, and we are only just beginning to feel the depths of the shock it gave us.”

 

References:

Will Steffen, Wendy Broadgate, Lisa Deutsch, Owen Gaffney, and Cornelia Ludwig. The trajectory of the Anthropocene: The Great Acceleration. The Anthropocene Review, January 16, 2015 DOI: 10.1177/2053019614564785

Jan Zalasiewicz et al. When did the Anthropocene begin? A mid-twentieth century boundary level is stratigraphically optimal. Quaternary International, published online January 12, 2015; doi: 10.1016/j.quaint.2014.11.045

Smith, B.D., Zeder, M.A., The onset of the Anthropocene. Anthropocene (2013),http://dx.doi.org/10.1016/j.ancene.2013.05.001

Ellis, E.C., 2011. Anthropogenic transformation of the terrestrial biosphere. Philosophical Transactions of the Royal Society A 369, 1010–1035.

 

A Christmas Carol: Dickens and the Little Ice Age

Scrooge's third visitor,  by John Leech. London: Chapman & Hall, 1843. First edition. (From Wikimedia Commons)

Scrooge’s third visitor, by John Leech, 1843. (From Wikimedia Commons)

Charles Dickens was born on 7 February 1812. He had only 31, when began to write A Christmas Carol in September 1843. The book was published on 19 December 1843. The novella tells the story of  Ebenezer Scrooge, a bitter old man who finds salvation through the visits of the three Ghosts of Christmas (Ghost of Christmas Past, Ghost of Christmas Present, and Ghost of Christmas Yet to Come). Dickens divided the story in five “staves”, where he describes the brutal winter and the horrors of social inequality. Scrooge is considered to be the very embodiment of winter: “No wind that blew was bitterer than he, no falling snow was more intent upon its purpose, no pelting rain less open to entreaty.”

Dickens describe the severe weather in many parts of the book: “…and they stood in the city streets on Christmas morning, where (for the weather was severe) the people made a rough, but brisk and not unpleasant kind of music in scraping the snow from the pavement in front of their dwellings, and from the tops of their houses, whence it was mad delight to the boys to see it come plumping down into the road below, and splitting into artificial little snow-storms.

A Frost Fair on the Thames at Temple Stairs by Abraham Danielsz Hondius (Abraham de Hondt), circa 1684 (From Wikimedia Commons)

Dickens grew up during the coldest years of the Little Ice Age, between 1805 to 1820. Many of the Christmas stories that are popular today were written during that period and winter landscapes were commonly depicted by artists like Pieter Bruegel, Hendrick Avercamp,  and Abraham Hondius.

The Little Ice Age (LIA) was a period that extends from the early 14th century through the mid-19th century, during which the Northern Hemisphere suffered from severe and prolonged cold winters. The period between 1600 and 1800 marks the height of the Little Ice Age.

Volcanoes are a possible cause for the LIA. The Tambora eruption on April 10, 1815, released two million tons of debris and  sulphur components into the atmosphere.  The following year was known as “the year without summer”. Charles Lyell describes the eruption in his Principles of Geology: “Great tracts of land were covered by lava, several streams of which, issuing from the crater of the Tomboro Mountain, reached the sea. So heavy was the fall of ashes, that they broke into the Resident’s house at Bima, forty miles east of the volcano, and rendered it, as well as many other dwellings… The darkness occasioned in the daytime by the ashes in Java was so profound, that nothing equal to it was ever witnessed in the darkest night.”

Reconstructed depth of the Little Ice Age varies between different studies  (From Wikimedia Commons)

Reconstructed depth of the Little Ice Age varies between different studies (From Wikimedia Commons)

Dickens revitalized the traditions of Christmas and to Victorian England, Dickens was Christmas. But he also contributed to the popularity of geology with the creation of ideas and images for public consumption, such as he did in Bleak House, with the description of the streets of London where ancient lizards roamed, and volcanoes and quakes shocked the earth.

 

References:

Charles Dickens, A Christmas Carol, Chapman & Hall, 1843.

BOER, de J.Z. & SANDERS, D.T. (2002): Volcanoes in Human History: The Far-Reaching Effects of Major Eruptions. Princeton University Press: 295

Brian M. Fagan, The Little Ice Age: How Climate Made History 1300-1850 (2001), Basic Books.

Buckland, Adelene , ‘“The Poetry of Science”: Charles Dickens, Geology and Visual and Material Culture in Victorian London’, Victorian Literature and Culture, 35 (2007), 679–94 (p. 680).