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.

 

 

Darwin’s Fossil Mammals.

Portrait of Charles Darwin painted by George Richmond (1840)

Portrait of Charles Darwin painted by George Richmond (1840)

When Charles Darwin arrived to South America, he was only 22 years old. He was part of the second survey expedition of HMS Beagle. During the first two years of his voyage aboard HMS Beagle, Darwin collected a considerable number of fossil mammals from various South American localities. He sent all the specimens, to his mentor John Stevens Henslow. The samples were deposited in the Royal College of Surgeons where Richard Owen began its study. Between 1837 and 1845, Owen described eleven taxa, including: Toxodon platensis, Macrauchenia patachonica, Equus curvidens, Scelidotherium leptocephalum, Mylodon darwinii and Glossotherium sp. Previous to this expedition, the first news of “fossils” in South American were reported by early Spanish explorers, and George Cuvier, in 1796,  published the first scientific work about Megatherium americanum, based on the specimen recovered by Fray Manuel Torres from Lujan, Buenos Aires, Argentina.

Darwin recovered his first fossil at Punta Alta (Buenos Aires Province, Argentina) on September 23, 1832, and continued collecting intermittently at this locality until October 16. Later, he went to Monte Hermoso and returned to Punta Alta between August 29 – 31, 1833. Then, he moved to Guardia del Monte (Buenos Aires Province); the Rio Carcarañá (Santa Fe Province, Argentina), and the Bajada Santa Fe (Paraná, Entre Ríos Province, Argentina). After a short stay in Uruguay, Darwin returned to Argentina and collected his last specimens at Puerto San Julián (Santa Cruz Province) in 1834. During his journey between Buenos Aires and Santa Fe he wrote “We may therefore conclude that the whole area of the Pampas is one wide sepulchre for these extinct quadrupeds” (Voyage of the Beagle, Chapter VII, Oct. 1833).

Fossil Toxodon on display at Bernardino Rivadavia Natural Sciences Museum.

Fossil Toxodon on display at Bernardino Rivadavia Natural Sciences Museum.

Toxodon was named by Owen based on a large skull purchased by Darwin. He paid 18 pence for it. Darwin described it as “one of the strangest animals, ever discovered…” Owen bestowed the name because its upper incisors were strongly arched (Toxodon means “arched tooth”). He also recognized Toxodon as “A gigantic extinct mammiferous animal, referable to the Order Pachydermata, but with affinities to the Rodentia, Edentata, and Herbivorous Cetacea”. Toxodonts shares a number of dental, auditory and tarsal specializations. They had  short hippopotamus-like head with broad jaws filled with bow shaped teeth and incisors, a massive skeleton with short stout legs with three functional toes. The estimated weight is over a tonne. About the different groups that appeared to be related to Toxodon, Darwin stated:“How wonderfully are the different orders, at the present time so well separated, blended together in different points of the structure of Toxodon”

A recent phylogenetic analysis indicates that Toxodon is most closely related to perissodactyls, a group that includes rhinos, tapirs, and horses.

Macrauchenia patachonica by Robert Bruce Horsfall.

Macrauchenia patachonica by Robert Bruce Horsfall.

Macrauchenia, meaning “big neck,” was named by Owen based on limb bones and vertebrae collected by Darwin in January 1834 at Puerto San Julian, in Santa Cruz Province, Argentina. The bizarre animal had a camel-like body, with sturdy legs, a long neck and a relatively small head. Owen described as “A large extinct Mammiferous Animal, referrible to the Order Pachydermata; but with affinities to the Ruminantia, and especially to the Camelidae”. Macrauchenia is now considered among the more derived native South American litopterns. Darwin also made inferences about the environment which Macrauchenia lived: “Mr. Owen… considers that they form part of an animal allied to the guanaco or llama, but fully as large as the true camel. As all the existing members of the family of Camelidae are inhabitants of the most sterile countries, so we may suppose was this extinct kind… It is impossible to reflect without the deepest astonishment, on the changed state of this continent. Formerly it must have swarmed with great monsters, like the southern parts of Africa, but now we find only the tapir, guanaco, armadillo, capybara; mere pigmies compared to antecedents races… Since their loss, no very great physical changes can have taken place in the nature of the Country. What then has exterminated so many living creatures?…We are so profoundly ignorant concerning the physiological relations, on which the life, and even health (as shown by epidemics) of any existing species depends, that we argue with still less safety about either the life or death of any extinct kind” (Voyage of the Beagle, Chapter IX, Jan. 1834).

Scelidotherium leptocephalum, Muséum national d'Histoire naturelle, Paris (From Wikimedia Commons)

Scelidotherium leptocephalum, Muséum national d’Histoire naturelle, Paris (From Wikimedia Commons)

Darwin recovered fossil remains of at least five species of giant ground sloth. In a letter sent to John Stevens Henslow in November, 1832, Darwin listed the fossils collected, among which he emphasized “… the upper jaw & head of some very large animal, with 4 square hollow molars — & the head greatly produced infront. — I at first thought it belonged either to the Megalonyx or Megatherium.” Darwin decided in favor of Megatherium based on the presence of osteoderms collected in the same formation, but Owen (1838-1840) recognized the specimens assigned by Darwin to Megatherium as glyptodonts, toxodonts, and large ground sloths (Fernicola et al., 2009; Allmon 2015). Scelidotherium, was described by Owen on the basis of the only nearly complete skeleton found by Darwin at Punta Alta (Buenos Aires Province). Darwin considered the specimen as “allied to the Rhinoceros”. Scelidotherium is distinctive by an elongated, superficially anteater-like head. Another sloth, Mylodon was named by Richard Owen on the basis of a nearly complete lower jaw with teeth, which was found by Charles Darwin at Punta Alta (Buenos Aires Province). Owen (1839b) erected Mylodon for two species, Mylodon darwini and Mylodon harlani. The former species was based on a left dentary from Punta Alta (Buenos Aires Province), whereas the second was based on a cast of a mandible from North America.

Fossil mammals collected by Charles Darwin in South America during the voyage of H.M.S. Beagle (From Allmon, 2015).

Fossil mammals collected by Charles Darwin in South America during the voyage of H.M.S. Beagle (From Allmon, 2015).

Darwin also found fossil horse teeth assignable to the modern genus Equus. The two molars from Argentina were recovered from Punta Alta (Buenos Aires Province) and Bajada Santa Fe (Entre Rios Province), and represent the first fossil horses found in South America. He wrote: “Certainly it is a marvellous event in the history of animals that a native kind should have disappeared to be succeeded in after ages by the countless herds introduced with the Spanish colonist! (1839, p. 150).

By the end of the expedition, Darwin was already earned a name as a geologist and fossil collector. He narrated his experiences in his book “Journal of Researches into the Geology and Natural History of the Various Countries visited by H.M.S. Beagle, under the Command of Captain FitzRoy, R.N. from 1832 to 1836″, published in 1839 and later simply known as “The Voyage of the Beagle”. When Darwin wrote his memories in 1858, he described the expedition in one strong and powerful sentence: “the voyage of the Beagle has been by far the most important event in my life and has determined my whole career”.

 

References:

Warren D. Allmon (2015): Darwin and palaeontology: a re-evaluation of his interpretation of the fossil record, Historical Biology, DOI: 10.1080/08912963.2015.1011397

Fernicola JC, Vizcaíno SF, de Iuliis G. 2009. The fossil mammals collected by Charles Darwin in South America during his travels on board the HMS Beagle. Revista de la Asocición Geológica Argentina. 64(1):147–159.

Fariña, Richard A.; Vizcaíno, Sergio F.; De Iuliis, Gerry (2013). Megafauna. Giant Beasts of Pleistocene South America. Indiana University Press.

 

Palynology of the Ischigualasto Formation.

Ischigualasto-perfil-gusano-montañas

Image from Ischigualasto Park (http://www.ischigualasto.gob.ar/)

Ischigualasto is an arid, sculpted valley, in northwest Argentina (San Juan Province), limiting to the north with the Talampaya National Park, in La Rioja Province. Both areas belong to the same geological formation: the Ischigualasto-Villa Unión Basin which is centered on a rift zone that accumulated thick terrestrial deposits during the Triassic. This basin preserves a complete and continuous fossiliferous succession of continental Triassic rocks.

The Ischigualasto Formation is known worldwide for its tetrapod assemblage, which included the oldest known record of dinosaurs. Adolf Stelzner in 1889 published the first data on the geology of Ischigualasto, but it was not until 1911, that Bondenbender briefly refers to the fossils of the site. Several thin volcanic ash horizons, indicates that the deposition of the Ischigualasto Formation began at the Carnian Stage (approximately 228 mya), and consists of four lithostratigraphic members which in ascending order include the La Peña Member, the Cancha de Bochas Member, the Valle de la Luna Member, and the Quebrada de la Sal Member.

1–3. Retusotriletes herbstii sp. nov; 4–5. Rogalskaisporites cicatricosus; 6. Rugulatisporites

1–3. Retusotriletes herbstii sp. nov; 4–5. Rogalskaisporites cicatricosus; 6. Rugulatisporites

During the Late Triassic two distinct microfloras have been recognised in the southern hemisphere: the Ipswich microflora and the Onslow microflora. The Ipswich province, characterized by the abundance of bisaccate pollen, monosulcate pollen and trilete spores, evolved in southern and eastern Australia, Transantarctic Mountains region, South Africa and Argentina. The Onslow province is a mixture of Gondwanan and European taxa recognized in of north-western Australia, Madagascar, East Africa, Indian, and East Antarctic (Cesari and Colombi; 2013).

The recognition of Carnian European species in the Valle de la Luna Member of the Ishchigualasto Formation expands the distribution of the Onslow-type palynofloras. This assemblage was recovered from the site known as “El Hongo” in the Provincial Park, and contain the diagnostic “Onslow” species: Samaropollenites speciosus, Enzonalasporites vigens, Patinasporites densus, Vallatisporites ignacii, Ovalipollis pseudoalatus and Cycadopites stonei. This assemblage indicates that the Valle de la Luna Member was likely deposited under more humid conditions. It also implies the existence of a latitudinal floral belt from Timor (through the Circum-Mediterranean area) to western Argentina.

 

References:

Cesari, Silvia N., Colombi, Carina, Palynology of the late Triassic ischigualasto formation, Argentina: Paleoecological and paleogeographic implications, Palaeogeography, Palaeoclimatology, Palaeoecology (2016), doi: 10.1016/j.palaeo.2016.02.023

Césari, S. N., Colombi, C. E., 2013. A new Late Triassic phytogeographical scenario in westernmost Gondwana. Nature communications, 4.

Spalletti, L. A. Artabe, A. E. & Morel, E. M. Geological factors and evolution of southwestern Gondwana Triassic plants. Gondwana Res. 6, 119–134 (2003).

 

The Pliocene Warm Period, an analogue of a future warmer Earth.

 

Tuktoyuktuk Beach on the Arctic Ocean (From Wikipedia)

Tuktoyuktuk Beach on the Arctic Ocean (From Wikipedia)

Microfossils from deep-sea are crucial elements for our understanding of past and present oceans. Their skeletons take up chemical signals from the sea water, in particular isotopes of oxygen and carbon. Over millions of years, these skeletons accumulate in the deep ocean to become a major component of biogenic deep-sea sediments. The incorporation of Mg/Ca into the calcite of marine organisms, like foraminifera, is widely used to reconstruct the thermal evolution of the oceans throughout the Cenozoic. Planktic foraminifer Globigerinoides ruber is perhaps one of the most widely used species for reconstructing past sea-surface conditions. Additionally, Mg/Ca–oxygen isotope measurements of benthic foraminifera may be related to global ice volume and by extension, sea level (Evans et al., 2016). 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 contains clues about the temperatures in which they lived.

Scanning Electron Micrographs of Globigerinoides ruber (adapted from Thirumalai et al., 2014)

Scanning Electron Micrographs of Globigerinoides ruber (adapted from Thirumalai et al., 2014)

The most recent investigations have focused on unravelling the Pliocene Warm Period, a period proposed as a possible model for future climate. The analysis of the evolution of the major ice sheets and the temperature of the oceans indicates that during the middle part of the Pliocene epoch (3.3 Ma–3 Ma), global warmth reached temperatures similar to those projected for the end of this century, about 2°–3°C warmer globally on average than today.

The mid-Pliocene is used as an analog to a future warmer climate because it’s geologically recent and therefore similar to today in many aspects like the land-sea configuration, ocean circulation, and faunal and flora distribution. Mid- Pliocene sediments containing fossil proxies of climate are abundant worldwide, and many mid- Pliocene species are extant, making faunal and floral paleotemperature proxies based on modern calibrations possible (Robinson et al., 2012).

Surface air temperature anomalies of (top) the late 21st century and (bottom) the mid-Pliocene (from Robinson et al., 2012)

Surface air temperature anomalies of (top) the late 21st century and (bottom) the mid-Pliocene (from Robinson et al., 2012)

Foraminiferal Mg/Ca data suggest that the Pliocene tropics were the same temperature or cooler than present. At high latitudes, mid- Pliocene sea surface temperatures (SSTs) were substantially warmer than modern SSTs. These warmer temperatures were reflected in the vegetation of Iceland, Greenland, and Antarctica. Coniferous forests replaced tundra in the high latitudes of the Northern Hemisphere. Additionally, the Arctic Ocean may have been seasonally free of sea-ice, and were large fluctuations in ice cover on Greenland and West Antarctica (Dolan et al., 2011; Lunt et al., 2012).  These results highlights the importance of the Pliocene Warm Period to better understand future warm climates and their impacts.

Reference:

David Evans, Chris Brierley, Maureen E. Raymo, Jonathan Erez, Wolfgang Müller; Planktic foraminifera shell chemistry response to seawater chemistry: Pliocene–Pleistocene seawater Mg/Ca, temperature and sea level change; Earth and Planetary Science Letters, Volume 438, 15 March 2016, Pages 139-148

Jochen Knies, Patricia Cabedo-Sanz, Simon T. Belt, Soma Baranwal, Susanne Fietz, Antoni Rosell-Mel. The emergence of modern sea ice cover in the Arctic Ocean. Nature Communications, 2014; 5: 5608 DOI: 10.1038/ncomms6608

Robinson, M.; Dowsett, H. J.; Chandler, M. A. (2008). “Pliocene role in assessing future climate impacts”; Eos 89 (49): 501–502.

Dorothea Bate: cave explorer and paleontologist.

dorothea bate

Dorothea Bate excavating in Bethlehem 1935.

During the 18th and 19th centuries women’s access to science was limited, and science was usually a ‘hobby’ for intelligent wealthy women. A good example is Barbara Hastings (1810–1858), 20th Baroness Grey de Ruthyn and Marchioness of Hastings. A special case was Mary Anning, ‘the greatest fossilist the world ever knew’. Scientists like William Buckland or Henry de la Beche owe their achievements to Mary’s work. 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.

Dorothea Bate was one of these pioneer women. She was born in Carmarthen in South Wales in 1878.  She was one of the last generation of Victorians, and witnessed the significant challenge to traditional ideas about women’s submissive place within society. When Dorothea was 10 years old, her family moved to South Wales where she begins to collect insects, stones, fossils, ferns, and flowers. She also learned how to dissect birds and small mammals. Her first passion was ornithology, and when she was 19, she went to London and asked for a job at the British Museum. She was taken to the Bird Room. That was the beginning of her association with the British Museum that was to last for more than 50 years.

Dorothea Bate c. 1906, by her sister Leila Luddington.

Dorothea Bate drawing by her sister Leila Luddington (1906).

Her first paper , published by Henry Woodward in the Geological Magazine in 1901, was a report on the Wye valley fossils. In the paper, she describes the fossils of small rodents from the last ice age recovered from the “Merlin’s Cave”, a place particularly dangerous to reach. That same year, she embarked on the first of her pioneering explorations of the Mediterranean islands. She visited Cyprus and became the first paleontologist to search systematically the limestone caves of the island and discover its extinct fossil fauna. In 1904, she went to Crete, then the scene of spectacular archaeological discoveries. In Cyprus and Crete, Dorothea found the fossilized remains of dwarf elephant, Elephas cypriotes Bate and Elephas creticus Bate (Bate 1903, 1907).

In 1909, after a five-year hiatus resulting in part from her parents’ reluctance to allow her to travel abroad alone, she went to the Balearic Islands. Invited by her good friend the Reverend Robert Ashington Bullen, Dorothea started her journey in Mallorca, where she discovered and described a bizarre goat-antelope with rat-like teeth, which she named Myotragus balearicus. Between 1903 and 1914, Dorothea wrote more than 15 papers on her Mediterranean discoveries. Unfortunately, in the early 1900s, a woman could not be elected a fellow of a learned society, nor present her own paper, so Henry Woodward presented them for her.

Dorothea Bate in 1938 (Copyright Natural History Museum, London.)

Dorothea Bate in 1938 (Copyright Natural
History Museum, London.)

In 1924, although women remained ineligible for permanent staff positions, Dorothea was named Curator of Aves and Pleistocene Mammals. She worked at Mount Carmel with Cambridge archaeologist and prehistorian, Dorothy Garrod, in a pioneering work on the relationship between fauna, climate change and the environment. In 1940 she was awarded with the prestigious Wollaston Fund of the Geological Society. Shortly after, she was elected a Fellow of this Society. Eight years later, she was appointed Officer-in-Charge of the Tring Museum in Hertfordshire, an outpost where the Natural History Museum’s collections had been evacuated during World War Two.

Despite her delicate health, she continued working until her dead on 13 January 1951.

References:

SHINDLER, K. (2007): A knowledge unique: the life of the pioneering explorer and palaeontologist, Dorothea Bate (1878-1951).

BUREK, C. V. & HIGGS, B. (eds) The Role of Women in the History of Geology. Geological Society, London, Special Publications, 281, 1–8. DOI: 10.1144/SP281.1.

Bate, D.M.A. 1914. On the Pleistocene ossiferous deposits of the Balearic islands. Geological Magazine, 6: 337-345.

Wyse Jackson, Patrick N.; Mary E. Spencer Jones (2007). “The quiet workforce: the various roles of women in geological and natural history museums during the early to mid-1900s”, Geological Society of London. pp. 97–113.

 

 

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 First 100 Million Years of Avian History.

The basal avian Sapeornis chaoyangensis (From Wikimedia Commons)

The basal avian Sapeornis chaoyangensis (From Wikimedia Commons)

Birds originated from a theropod lineage more than 150 million years ago. By the Early Cretaceous, they diversified, evolving into a number of groups of varying anatomy and ecology. In recent years, several discovered fossils of theropods and early birds have filled the morphological, functional, and temporal gaps along the line to modern birds. Most of these fossils are from the Jehol Biota of northeastern China, dated between approximately 130.7 and 120 million years ago. The Jehol Biota is formed from two formations: the Yixian Formation, and the Jiufotang Formation, and contain the most diversified avifauna known to date. Among them was the long bony-tailed Jeholornis, only slightly more derived than Archaeopteryx, that lived with Sapeornis, Confuciusornis, and the earliest members of Enantiornithes and Ornithuromorpha. The last two groups, form the clade Ornithothoraces, characterized by a keeled sternum, elongate coracoid, narrow furcula, and reduced hand.

Ornithuromorphs, include Gansus, Patagopteryx, Yixianornis, and Apsaravis, which form a grade on the line to Ornithurae, a derived subgroup that includes modern birds and their closest fossil relatives (Brusatte et al., 2015).

The single best record of a Cretaceous neornithine is the partial skeleton of Vegavis from the latest Cretaceous (around 68–66 million years ago) of Antarctica.

Zhenyuanlong suni (photo by Junchang Lu¨ ) from the Jehol Biota.

Zhenyuanlong suni (photo by Junchang Lu) from the Jehol Biota.

Anatomical features like aspects of egg shape, ornamentation, microstructure, and porosity of living birds trace their origin to the maniraptoran theropods, such as oviraptorosaurs and troodontids. In addition, some preserving brooding postures, are known for four oviraptorosaurs, two troodontids, a dromaeosaur, and one basal bird providing clear evidence for parental care of eggs.

In birds, particularly their forebrains, are expanded relative to body size. Birds also exhibit the most advanced vertebrate visual system, with a highly developed ability to distinguish colors over a wide range of wavelengths.

Feathers were once considered to be unique avialan structures. The megalosaurus Sciurumimus, the compsognathus Sinosauropteryx, and a few other dinosaurs, document the appearance of primitive feathers. Zhenyuanlong suni, from the Yixian Formation, provides the first evidence of well-developed pennaceous feathers in a large, non-flying dromaeosaur. Evidence indicates that the earliest feathers evolved in non-flying dinosaurs, likely for display and/or thermoregulation, and later were co-opted into flight structures in the earliest birds (Brusatte et al., 2015).

The basal avian Jeholornis prima.

The basal avian Jeholornis prima.

The evolution of flight involved a series of adaptive changes at the morphological and molecular levels, like the fusion and elimination of some bones and the pneumatization of the remaining ones. Archaeopteryx lacked a bony sternum and a compensatory specialized gastral basket for anchoring large flight muscles (O’Connor et al., 2015), while Jelohornis had several derived flight-related features of modern birds like fused sacral vertebrae, an elongated coracoid with a procoracoid process, a complex sternum, a narrow furcula, and curved scapula. In Enantiornithines, their robust pygostyle appears to have been unable to support the muscles that control the flight feathers on the tail in modern birds. The increased metabolism associated with homeothermy and powered flight requires an efficient gas exchange process during pulmonary ventilation. Recent anatomical and physiological studies show that alligators, and monitor lizards exhibit respiratory systems and unidirectional breathing akin to those of birds, which indicate that unidirectional breathing is a primitive characteristic of archosaurs or an even more inclusive group with the complex air-sac system evolving later within Archosauria.

The earliest diversification of extant birds (Neornithes) occurred during the Cretaceous period and after the mass extinction event at the Cretaceous-Paleogene (K-Pg) boundary, the Neoaves, the most diverse avian clade, suffered a rapid global expansion and radiation. A genome-scale molecular phylogeny indicates that nearly all modern ordinal lineages were formed within 15 million years after the extinction, suggesting a particularly rapid period of both genetic evolution and the formation of new species. Today, with more than 10500 living species, birds are the most species-rich class of tetrapod vertebrates.

 

References:

Brusatte, S. L., O’Connor, J. K., and Jarvis, E. D. 2015. The origin and diversification of birds. Current Biology, 25, R888-R898

Padian, K., and Chiappe, L.M. (1998). The origin and early evolution of birds. Biol. Rev. 73, 1–42.

Puttick, M. N., Thomas, G. H. and Benton, M. J. (2014), HIGH RATES OF EVOLUTION PRECEDED THE ORIGIN OF BIRDS. Evolution, 68: 1497–1510. doi: 10.1111/evo.12363 A.

Xing Xu, Zhonghe Zhou, Robert Dudley, Susan Mackem, Cheng-Ming Chuong, Gregory M. Erickson, David J. Varricchio, An integrative approach to understanding bird origins, Science, Vol. 346 no. 6215, DOI: 10.1126/science.1253293.

Letters from Father Tolkien.

tolkien

John Ronald Reuel Tolkien was born on January 3, 1892, in Bloemfontein, South Africa, and died on September 2, 1973, in Bournemouth, England. He grew up in the waning days of the Victorian Era, and died along with the Swinging London. He saw the horror of the war, and the memories of his experiences as an officer in World War I were sublimated in his fiction. As he wrote in the Introduction to the second edition of The Lord of the Rings: “it seems now often forgotten that to be caught by youth in 1914 was no less hideous an experience than to be involved in 1939 and the following years. By 1918 all but one of my close friends were dead”.

He started writing stories for his children as early as 1920, when he first sent to John, the eldest son, a letter purporting to be from Father Christmas. The letters were written over a period of 20 years to entertain Tolkien’s children each Christmas. He also created the envelopes, and designed his own stamps. In the letters, Tolkien documented the adventures and misadventures of Father Christmas and his helpers. There are some similarities between the early letters and The Hobbit. Even more, Laurence and Martha Krieg in the journal Mythlore suggested that Gandalf himself may have been developed from Father Christmas.

FatherChristmasLetters_1932

Cave Drawings with Goblin Graffiti from the Father Christmas Letter of 1932.

In the letter for 1932, Father Christmas rescues the North Polar Bear from the caves and finds Goblin wall paintings. It’s a wonderful piece full of mammoths, bison, and goblin scribblings. Tolkien wrote: “must be very old, because the Goblin fighters are sitting on drasils: a very queer sort of dwarf ‘dachshund’ horse creature… I believe the Red Gnomes finished them off, somewhere about Edward the Fourth’s time.” 

It has been suggested that the painting was copied from Baldwin Brown’s The Art of the Cave Dweller: A Study of the Earliest Artistic Activities of Man. In his work, Brown emphasized that the primitive hunter must naturally have become a keen observer of nature. The first cave paintings were found in 1870 in Altimira, Spain. The Lascaux Caves, near the village of Montignac, in France, contain some of the best-known Upper Paleolithic art, estimated in 17,300 years old. During the Pleistocene and the early Holocene, most of the terrestrial megafauna became extinct. It was a deep global-scale event. Europe witnessed the extinction of several large mammalian herbivores, such as steppe bison Bison priscus, woolly mammoth Mammuthus primigenius, woolly rhinoceros Coelodonta antiquitatis and giant deer Megaloceros giganteus. The patterns exhibited by the Late Quaternary megafauna extinction (LQE) indicated a close link with the geography of human evolution and expansion.

Tolkien also anticipated some of the tenets of modern environmentalism in the imagined world of Middle-earth and the races with which it is peopled.

References:

The Father Christmas Letters. By J.R.R. Tolkien; Allen and Unwin (1976).

THE ART OF THE CAVE DWELLER: a study of the earliest Artistic Activities of Man. By G. Baldwin Brown. John Murray. 1928. pp. xix, 280. 18s.

 

 

The Chañares Formation and the origin of dinosaurs.

The Chañares Formation (© 2012 Idean)

The Chañares Formation (© 2012 Idean)

The Chañares Formation crops out in the Ischigualasto-Villa Unión Basin, formed along the western margin of South America  during the  breakup  of  Gondwana. It represents one of the most continuous continental Triassic succesions in South America. These beds were explored by Alfred Romer and Jensen (1966) in their report on the geology of the Rio Chañares and Rio Gualo region.

Located in Talampaya National Park (La Rioja Province), the Chañares Formation is characterized at its base by a sandstone–siltstone fluvial facies with distinct lower and upper levels. The lower levels are composed of light olive grey fine-grained sandstones with abundant small brown carbonate concretions. The upper levels include fine-grained sandstones and siltstones that preserve vertebrate remains (Mancuso et al., 2014).

Geological map of the Chañares–Gualo area in Talampaya National Park (From Marsicano et al., 2015)

Geological map of the Chañares–Gualo area in Talampaya National Park (From Marsicano et al., 2015)

Volcanism played an important role in the generation and preservation of the Chañares Formation’s exceptional tetrapod fossil record. The diverse and well-preserved tetrapod assemblage includes proterochampsids, pseudosuchians, ornithodirans, large dicynodonts and smaller cynodonts. Almost all dinosauromorphs are preserved in diagenetic concretions that erode out of a thick siltstone interval 15–20 m above the base of the formation, and include Lagosuchus talampayensis, Marasuchus lilloensis Lewisuchus admixtus and Pseudolagosuchus major.

Analysing the ratio of U–Pb inside the zircon crystals found in the rocks assigns the Chañares Formation to the Late Triassic, specifically the early Carnian (236–234 Ma), between 5 to 10 million years younger than previous estimate. This also suggests a similarly age for the lower Santa Maria Formation in southern Brazil, because it shares with the Chañares assemblage a variety of tetrapod genera and species unknown from anywhere else. The new results provide the basis to construct a robust framework for calibrating the timing of macro-evolutionary patterns related to the origin and early diversification of dinosaurs in Gondwana (Marsicano et al., 2015). It also suggests there was little compositional difference between the Chañares assemblage and the earliest dinosaur assemblage from the lower part of the Ischigualasto succession, where dinosauromorphs (including dinosaurs) are a minority, with synapsids still dominant. Only 15 million years later dinosaurs begin to dominate the ecosystem.

Artist’s reconstruction of the Chanares environment during the Middle Triassic. (From Mancusso et al., 2014. Art by Jorge Fernando Herrman.)

Artist’s reconstruction of the Chanares environment during the Middle Triassic. (From Mancusso et al., 2014. Art by Jorge Fernando Herrman.)

 

References:

Marsicano, C. A., Irmis, R. B., Mancuso, A. C., Mundil, R. & Chemale, F., The precise temporal calibration of dinosaur origins, Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1512541112 (2015).

Brusatte SL, et al. (2010) The origin and early radiation of dinosaurs. Earth Sci Rev 101:68100.

Mancuso AC, Gaetano LC, Leardi JM, Abdala F, Arcucci AB (2014) The ChañaresFormation: A window to a Middle Triassic tetrapod community. Lethaia 47:244265.

Romer AS, Jensen J (1966) The Chañares (Argentina) Triassic reptile fauna. II. Sketch of the geology of the Rio Chañares, Rio Gualo region. Breviora 252:1–20.