Thursday, 23 January 2020

Asteroid 2020 AN3 passes the Earth.

Asteroid 2020 AN3 passed by the Earth at a distance of about 3 045 800 km (7.93 times the average distance between the Earth and the Moon, or 2.04% of the distance between the Earth and the Sun), at about 1.35 am GMT on Friday 17 January 2020. There was no danger of the asteroid hitting us, though were it to do so it would have presented a considerable threat. 2020 AN3 has an estimated equivalent diameter of 160-500 m (i.e. it is estimated that a spherical object with the same volume would be 160-500 m in diameter), and an object of this size would be predicted to be capable of passing through the Earth's atmosphere relatively intact, impacting the ground directly with an explosion that would be 10 000-300 000 times as powerful as the Hiroshima bomb. Such an impact would result in an impact crater 2.5-8 km in diameter and devastation on a global scale, as well as climatic effects that would last decades or even centuries.

180 second image of 2020 AN3 taken with the Elena Planetwave 17" Telescope at Ceccano in Italy on 16 January 2020. The asteroid is the small point at the centre of the image, the longer lines are stars, their elongation being caused by the telescope tracking the asteroid over the length of the exposure. Gianluca Masi/Virtual Telescope.

2020 AN3 was discovered on 14 January 2020 (three days before its closest approach to the Earth) by the University of Arizona's Catalina Sky Survey, which is located in the Catalina Mountains north of Tucson. The designation 2020 AN3 implies that it was the 85th asteroid (object N3 - in numbering asteroids the letters A-Y, excluding I, are assigned numbers from 1 to 24, so that N3 = (24 x 3) + 13 = 85) discovered in the first half of January 2020 (period 2020 A).

The calculated orbit of 2020 AN3. Minor Planet Center.

2020 AN3 has an 1158 day (3.17 year) orbital period and an eccentric orbit tilted at an angle of 26.3° to the plane of the Solar System, which takes it from 0.97 AU from the Sun (i.e. 97% of the the average distance at which the Earth orbits the Sun) to 3.35 AU from the Sun (i.e. 335% of the average distance at which the Earth orbits the Sun, and more than twice as distant from the Sun as the planet Mars). It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). This means that close encounters between the asteroid and Earth are extremely common, with the last having occurred in January 2001 and the next predicted in December 2035. As an asteroid probably larger than 150 m in diameter that occasionally comes within 0.05 AU of the Earth, 2019 AV2 is also classified as a Potentially Hazardous Asteroid.

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Wednesday, 22 January 2020

Fluctuations in mercury and organic carbon in the peatlands of southwest China before the End Permian Extinction.

Carbon has two stable isotopes, carbon¹² and carbon¹³, of which plants preferentially incorporate carbon¹² into their tissues as it requires less energy to fix; this means that sediments with a high plant-derived carbon content (such as coal bed) will tend to be enriched in carbon¹² relative to sediment without (such as marine limestones). Furthermore, an increase in carbon in the atmosphere from burning plant matter, either as forests or coal beds, will tend to lead to an increase in the relative amount of carbon¹² in all sediments, known to geochemists as a positive organic carbon isotope excursion, whereas an increase in atmospheric carbon from other sources, such as volcanic eruptions, will tend to lead to a a drop in carbon¹² in all sediments, or a negative organic carbon isotope excursion.The Permian-Triassic mass extinction was the most severe extinction event of the Phanerozoic, both in marine and terrestrial settings, but the relative timing of these crises is debated. A negative carbon isotope excursion in both carbonate and organic matter is seen at the main extinction horizon and is usually attributed to release of volcanic carbon. Most proposed kill mechanisms for the Permian-Triassic mass extinction are linked to the effects of Siberian Traps eruptions. A spike in mercury concentrations observed at the onset of the Permian-Triassic mass extinction, thought to be derived from Siberian eruptions, provides a chemostratigraphic marker in marine records. A similar mercury enrichment event has also been documented in contemporaneous terrestrial sediments. Marine records show widespread environmental instability prior to the Permian-Triassic mass extinction, and a new study of the Sydney Basin (New South Wales, Australia), suggests that the collapse of southern high-latitude floras occurred significantly before the onset of marine extinctions roughly coincident with onset of northern high latitude marine stress.

In a paper published in the journal Geology on 3 January 2020, Daoliang Chu of the State Key Laboratory of Biogeology and Environmental Geology at the China University of Geosciences, Stephen Grasby of the Geological Survey of Canada, Haijun Song, also of the State Key Laboratory of Biogeology and Environmental Geology at the China University of Geosciences, Jacopo Dal Corso of the School of Earth and Environment at the University of Leeds, Yao Wang, again of the State Key Laboratory of Biogeology and Environmental Geology at the China University of Geosciences, Tamsin Mather of the Department of Earth Sciences at the University of Oxford, Yuyang Wu, Huyue Song, Wenchao Shu, and Jinnan Tong, once again of the State Key Laboratory of Biogeology and Environmental Geology at the China University of Geosciences, and Paul Wignall, also of the School of Earth and Environment at the University of Leeds, evaluate the timing and nature of the terrestrial crisis at the End of the Permian in southwest China by examining variations in fossil charcoal abundance from paleo–tropical peatlands to explore changes in wildfire occurrence and the carbon-isotope composition of land plant cuticles, charcoal, and bulk organic matter to track changes in the isotopic composition of atmospheric carbon dioxide. In addition they investigated sedimentary mercury concentrations, and the integration of their record with carbon isotope values permits chemostratigraphic correlation of terrestrial and marine records.

Chu et al. examined the continental Permian-Triassic transition in cored borehole ZK4703, drilled 15 km south of Fuyuan County in Yunnan Province, China, and the Chinahe outcrop section, 30 km southeastern of Xuanwei City, both from the border area between western Guizhou and eastern Yunnan in southwestern China. Latest Permian to earliest Triassic terrestrial strata in this region include, in ascending order, the fluvial-coastal swamp facies of the Xuanwei and Kayitou Formations. The former consists of sandstone, mudstone, and common coal beds. The associated plant fossils belong to the Gigantopteris flora and include Pecopterids (Tree Ferns), Gigantopterids (a morphologically advanced group of Permian Vascular Plants that disappeared in the End Permian Extinction), Lycopsiales (Giant Club Mosses), and Equisetales (Horsetails) taxa, collectively regarded as tropical rainforest-type vegetation. The Kayitou Formation (latest Permian to earliest Triassic age) is similar to the underlying Xuanwei Formation, but lacks coal and is shale dominated. Previous studies showed that the loss of the Gigantopteris flora occurred in the lowest Kayitou Formation.

Late Permian to Early Triassic palaeogeographic map showing locations of the ZK4703 core (25.54151°N, 104.28994°E) and the Chinahe section (26.13077°N, 104.35637°E) in southwestern China, and the Meishan section, south China. Chu et al. (2020).

Organic carbon isotopes, charcoal abundance, fossil plant ranges, total organic carbon, total sulphur concentrations, and aluminium and Mercury contents were assessed through the Permian-Triassic transition in the ZK4703 core and at the Chinahe outcrop. To avoid facies variation issues, only mudstone samples were processed for charcoal. Some charcoal was examined under scanning electron microscope to confirm identification. To ensure that the charcoal concentrations were not affected by variations in the nature or abundance of organic material, its abundance was normalised to phytoclast abundance and total organic carbon.

 Location map of the studied section. Chinahe section (26.13077°N, 104.35637°E) is located in the Chinahe Viliage of the Tianba town, Xuanwei City. ZK4703 core (25.54151°N, 104.28994°E), drilled in Anzichong Viliage of Dahe Town, Qujing City. Chu et al. (2020).

The proportion of carbon¹² drops sharply in the lower part of the Kayitou Formation at Chinahe, both in organic matter and charcoal (a negative organic carbon isotope excursion). At the same time bulk organic matter and palynomorphs (pollen fossils) from the ZK4703 core section also show a drop in carbon¹² values.

Cuticle and charcoal particles under binocular microscope and scanning electron microscope. Chu et al. (2020).

The abundant, peat-forming Gigantopteris flora is seen at six levels in the Xuanwei Formation at Chinahe, and is dominated by well-preserved, large leaves. Both diversity and abundance of this flora decline drastically at the very top of the formation at a level that corresponds to the onset of the negative negative organic carbon isotope excursion. Thereafter, the flora consists of a monotonous assemblage of small plants, mostly Annalepis and Peltaspermum.

 Typical Gigantopteris flora from the Xuanwei Formation of the Chinahe section. (A) Gigantopteris dictyophylloides; (B) Annularia pingloensis; (C) Lobatannularia sp.; (D) Pecopteris marginata; (E) Gigantonoclea guizhouensis; (F) Pecopteris sp.; (G) Compsopteris contracta; (H) Abundant plant leaf fossils preserved on the same bedding surface. Chu et al. (2020).

At Chinahe, the charcoal abundance is less than 300 particles per 100 g rock prior to the a negative organic carbon isotope excursion, but rises briefly above background levels during the onset of the excursion (1524 particles per 100 g at 25 m log height), and ranges from 400 to 1600 particles per 100 g in the 4 m interval of the uppermost part of the Xuanwei Formation to lower part of the Kayitou Formation. Similarly, in the ZK4703 record there is a sharp increase in charcoal abundance, from under 400 particles per 100 g below 15 m, to over 2400 particles per 100 g above 16.5 m height at the base of the Kayitou Formation. Scanning electron microscope observation shows that the charcoal preserves anatomical details and has similar preservation and structures with variable size, indicating minimal transport sorting. The reported variations in charcoal abundance do not appear to be an artifact of preservation or changes in terrestrial organic delivery, because variations in preserved phytoclasts (microscopic plant fragments) and total organic carbon do not vary with charcoal abundance.

The plant fossil ranges and species richness of the Chinahe section. (1) Peltaspermum sp.; (2) Annalepis sp.; (3) Compsopteris contracta; (4) Fascipteris densata; (5) Cladophlebis permica; (6) Annularia pingloensis; (7) Compsopteris sp.; (8) Lobatannularia heianensis; (9) Pecopteris marginata; (10) Lobatannularia cathaysiana; (11) Pecopteris guizhouensis; (12). Rajahia guizhouensis; (13) Gigantonoclea sp.; (14) Stigmaria sp.; (15) Gigantonoclea guizhouensis; (16) Gigantopteris dictyophylloides; (17) Pecopteris sp.. Chu et al. (2020).

Mudstone total organic carbon concentrations are relatively high in the Xuanwei Formation and modestly enriched concentrations persist into the lower part of Kayitou Formation before dropping at the 27 m log height at Chinahe. Both overall mercury levels and the mercury-total organic carbon ratio rise above background levels immediately above the interval with the onset of the negative organic carbon isotope excursion and increased charcoal abundance. High overall mercury levels and the mercury-total organic carbon ratios can also be observed at higher stratigraphic levels, with a peak value at 19.75 m in the ZK4703 core, which is about 50 times background levels. Overall mercury levels and the mercury-total organic carbon ratio drop to the previous baseline values above 37 m at Chinahe and 25 m in ZK4703. The weak correlation between overall mercury levels and the mercury-total organic carbon ratios suggests that the mercury fluctuations are not affected by changes in total organic carbon. Additionally, the ZK4703 core has low total sulphur contents which show no significant covariation with mercury values. Correlation between Aluminium and Mercury concentrations is also weak, indicating that mercury fluctuations are not controlled primarily by clay content, even if some mercury is probably adsorbed onto clay. Nonetheless, there is secular variability in the mercury/aluminium ratio, with very low background mercury/aluminium values below and above the mercury anomaly and enriched mercury/aluminium values within the interval.

Volcanic emissions represent one of the largest natural inputs of mercury to the atmosphere, and the mercury enrichment seen in many marine Permian-Triassic boundary sequences is thought to record large-scale Siberian Traps eruptions. Volcanic mercury emissions from this source may have been up to 10 000 milligrammes per year (roughly 14 times natural background levels). Thermogenic release of mercury from baking of organic-rich sediments on contact with Siberian Traps intrusions is another potential source of mercury. Terrestrial plants constitute a large mercury reservoir, and so wildfires can also contribute significantly to mercury fluxes to the atmosphere and freshwater environments such as those studied by Chu et al., who propose that the mercury spikes observed in terrestrial and marine successions provide a useful correlative tool between terrestrial and marine records along with carbon isotope ratios.

The onset of the main phase of marine extinctions in South China, at the top of the Clarkina yini Zone, correlates with a peak in mercury concentrations and mercury/total organic carbon ratios, while a second phase of extinctions at the top of the Isarcicella staeschi Zone corresponds to a rise in mercury concentrations and mercury/total organic carbon ratios that peaks in the following Isarcicella isarcica Zone. The relative magnitude of these peaks varies between sections: at Meishan, South China, the lower mercury/total organic carbon ratios peak is the largest, whereas at Guryul Ravine, Kashmir, the second peak is larger. Levels of organic carbon began to decline somewhat before the marine extinctions in the Clarkina changxingensis Zone.

In the terrestrial sections of southwestern China, the floral mass extinction (and charcoal peak) starts with the onset of the negative organic carbon isotope excursion. Mercury concentrations begin to slightly rise at the same time, while mercury/total organic carbon ratios shows a sharp spike at the minimum of the negative organic carbon isotope excursion. The mercury and mercury/total organic carbon ratios peak 4–6 m above the terrestrial extinction level and likely correlate with the rise in mercury/total organic carbon ratios values seen at the end–Isarcicella staeschi Zone that saw diverse taxa disappear from Triassic oceans. Thus, the terrestrial crisis seen in equatorial sections of China appears to predate the main marine extinction phase (which occurred near the low point of negative organic carbon isotope excursion), and likely dates to the late Clarkina changxingensis Zone.

Chu et al.'s results demonstrate that a synchronous onset of the negative organic carbon isotope excursion is present in the bulk organic matter, cuticle, and charcoal carbon isotope records from terrestrial settings. Changes in organic carbon values of land plant cuticles record changes in atmospheric CO₂. Chu et al. suggest that the observed negative organic carbon isotope excursion in cuticles and fossil charcoal reflects an injection of carbon¹³-depleted emissions associated with the Siberian Traps. Interestingly, in our study, the peak in mercury concentrations and mercury/total organic carbon ratios also occurred after the onset of the negative carbon isotope excursion, suggesting a decoupling between the carbon and the mercury records that could result from the source of these two elements, be it volcanic, thermogenic, continental runoff, wildfire, or a combination of different reservoirs. Such decoupling deserves further investigation because it suggests different mechanisms of carbon and mercury release and/or processing in End Permian environments.

Studies have shown insignificant or constant fractionation of carbon isotopes during the burning process, and so charcoal carbon isotope ratios are a direct record of the original wood tissue carbon isotope ratios. The gradual decrease in the proportion of carbon¹³ in terrestrial plant-derived charcoal in the studied successions indicates, as discussed also for cuticle carbon isotope ratios, a change in the proportion of carbon¹³ in the original peat and vegetation due to changes in the proportion of carbon¹³ in the atmospheric CO₂. The charcoal carbon¹³ negative shift is coeval with an increase in charcoal abundance, i.e., with increased wildfire activity suggesting that the latest Permian forests experienced recurring wildfires and regrowth while the atmosphere became more carbon¹³ depleted. Additionally, burning of terrestrial plant biomass can also increase the emission of mercuty into the atmosphere, and then this mercury can be scavenged and buried in sediments.

The intensification of wildfire activity at the time of terrestrial mass extinction provides evidence of the harmful climatic changes in the lead-up to terrestrial crisis. The Gigantopteris coastal swamp flora thrived in humid, warm equatorial locations and was unlikely to have been adapted to intense levels of wildfire, as evidenced by the low charcoal abundance prior to the extinction interval. Thus, the increased wildfires suggest a transition to more unstable conditions punctuated by dry periods that would have been detrimental to coastal swamp floras. 

Chu et al.'s study sheds new light on the temporal links between the deterioration in the terrestrial environment and floral extinction, and the geochemical changes that mark the Permian-Triassic mass extinction. Their terrestrial mercury record from the Permian-Triassic transition shows a sharp peak contemporaneous with the disappearance of Permian flora that correlates with marine mercury records. Carbon isotope data from cuticles and fossil charcoal, thought to reflect changes in the carbon isotope composition of the atmosphere, show a negative carbon isotope excursion during the terrestrial flora mass extinction interval. However, this was prior to the increase in mercury concentrations. Charcoal abundance shows that the floral extinctions coincided with an increase of wildfire activity and the carbon-cycle disruption. This likely reflects a change from persistent humidity to an unstable climate with frequent drought episodes. The temporal relationships between the events show that terrestrial disruption occurred shortly (but measurably) before the marine crisis.

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Monday, 20 January 2020

Seven missing following avalanche on Mount Annapurna, Nepal.

Seven people are missing following a landslide on Mount Annapurna, Nepal, on Saturday 18 January 2020. The missing are described as three South Korean tourists, two men and a woman in their fifties, plus a woman in her thirties, plus three Nepalese tour guides. Several other parties of hikers who were in the area at the time were evacuated safely, but rescuers were unable to locate the missing party on Saturday, and could not return to the area due to poor weather, until late on Sunday, when it was found that their last known location was covered by snow five metres deep. It is thought unlikely that they have survived.

Rescue workers on Mount Annapurna, Nepal, on 18 January 2020. Phurba Ongel Sherpa/AP.

Avalanches are caused by the mechanical failure of snowpacks; essentially when the weight of the snow above a certain point exceeds the carrying capacity of the snow at that point to support its weight. This can happen for two reasons, because more snow falls upslope, causing the weight to rise, or because snow begins to melt downslope, causing the carrying capacity to fall. Avalanches may also be triggered by other events, such as Earthquakes or rockfalls. Contrary to what is often seen in films and on television, avalanches are not usually triggered by loud noises. Because snow forms layers, with each layer typically occurring due to a different snowfall, and having different physical properties, multiple avalanches can occur at the same spot, with the failure of a weaker layer losing to the loss of the snow above it, but other layers below left in place - to potentially fail later.

Diagrammatic representation of an avalanche, showing how layering of snow contributes to these events. Expedition Earth.

Mount Annapurna is a 55 km long massif reaching 8091 m above sealevel at its highest point, with sixteen more peaks that reach over 6000 m above sealevel, making it the tenth highest mountain in the world. Annapurna was the first mountain over 8000 m to be climbed (by Maurice Herzog in 1950), and is popular with both climbers and trekkers. Nonetheless, the mountain is considered to be one of the most dangerous high mountains in the world, with 61 known fatalities since 1990 (exceeded only by Mount Kangchenjunga, also in Nepal), including 43 people killed in a single storm in October 2014, which triggered a series of avalanches in areas popular with tourists.

The South Face of Mount Annapurna. Prajwal Mohan/Wikimedia Commons.

Nepal is located entirely within the Himalayas, a range of mountains formed by uplift associated with the collision between the Indian and Eurasian tectonic plates. The Indian Plate is moving northwards at a rate of 5 cm per year, causing it to impact into Eurasia, which is also moving northward, but only at a rate of 2 cm per year. When two tectonic plates collide in this way and one or both are oceanic then one will be subducted beneath the other (if one of the plates is continental then the other will be subducted), but if both plates are continental then subduction will not fully occur, but instead the plates will crumple, leading to folding and uplift (and quite a lot of Earthquakes). The collision of the Indian and Eurasian plates has lead to the formation of the Himalayan Mountains, the Tibetan Plateau, and the mountains of southwest China, Central Asia and the Hindu Kush.

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Three killed by explosion at chemical plant in Tarragona, Spain.

Three men have died and several more remain in serious conditions following an explosion at a chemical plant in the city of Tarragona in the Catalonia Region of Spain on Tuesday 14 January 2020. Two of the men worked at the plant, one of whom was killed instantly and the other died of his injuries the following day/ However, the third man, a 59-year-old identified only as Sergio, died in his home about 2.5 km from the blast, when the building was hit by the lid of the vessel in which the explosion occurred, described as a metal plate measuring 122 by 165 centimetres, and weighing about a tonne.

The trajectory followed by a metal plate thrown from an explosion at a chemical plant in Catalonia on 14 January 2020, killing a man 2.5 km from the site. El País.

The plant where the explosion occurred was manufacturing ethylene glycol, C₂H₄O, a highly volatile gas used primarily in the manufacture of ethylene glycol, which it the major component of most commercially available anti-freezes and a precursor of polyester. Ethylene oxide is an explosive gas at normal pressures and temperatures above -10°C, and is usually stored under pressure as a liquid. However, should a vessel containing ethylene oxide develop a leak, or otherwise be compromised, the escaping gas will remain explosive at even low concentrations in the atmosphere.

Fire caused by an explosion at a chemical plant in Taragona, Spain, on 14 January 2020. Reuters.

As well as being highly explosive, ethylene oxide is also toxic and carcinogenic, which led to residents of the area being ordered to remain inside their homes until it was certain that there was no release of toxic material, although the efficient combustion of the chemical proved to have made the incident safe quite quickly. In addition to the fatalities, a further seven workers at the plant were injured in the incident, with described as remaining in a serious condition at Barcelona’s Vall d’Hebron Hospital. Local civil defence authorities have expressed extreme concern that they were not informed of the event by the site's management, but rather were called by residents of the area, delaying access to the site by firefighters, who needed to ascertain the nature of the incident before entering the facility.

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Sunday, 19 January 2020

Magnitude 6.4 Earthquake in western Xinjoang Province, China.

The China Earthquake Networks Center recorded a Magnitude 6.4 Earthquake at a depth of 16 km in the Tian Shan Mountains of northwestern Xinjiang Province, China, slightly after 9.20 pm local time (slightly after 1.20 pm GMT) on Sunday 19 January 2020. There are no reports of any damage or injuries associated with this event, but it was felt across a wide area of Xinjiang Province and neighbouring Kyrgyzstan.
The approximate location of the 19 January 2020 Xinjiang Earthquake. USGS.
The Tian Shan Mountains stretch for 2500 km across Xinjiang, Kazakhstan, Kyrgyzstan and Uzbekistan. The Tian Shan are part of the Himalayan Orogenic Belt, mountains in Central Asia pushed upwards by the collision of India and Asia. The Indian Plate is currently pushing into the Eurasian Plate from the south at a rate of 3 cm per year. Since both are continental plates, which do not subduct, the Eurasian Plate is folding and buckling, causing uplift in the Himalayas and other mountains of Central Asia. This is not a smooth process, the rocks will remain effectively stationary for log periods of time while pressure builds up, then give suddenly, releasing large amounts of energy in the form of Earthquakes.

The movement of India relative to Asia, and the blocks within the eastern part if the Eurasian Plate. University of Wollongong.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organisation Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.

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