A fossil winonaite-like meteorite in Ordovician limestone: A piece of the impactor that broke up the L-chondrite parent body?

AbstractAbout a quarter of all meteorites falling on Earth today originate from the breakup of the L-chondrite parent body ∼470 Ma ago, the largest documented breakup in the asteroid belt in the past ∼3 Ga. A window into the flux of meteorites to Earth shortly after this event comes from the recovery of about 100 fossil L chondrites (1–21 cm in diameter) in a quarry of mid-Ordovician limestone in southern Sweden. Here we report on the first non-L-chondritic meteorite from the quarry, an 8 cm large winonaite-related meteorite of a type not known among present-day meteorite falls and finds. The noble gas data for relict spinels recovered from the meteorite show that it may be a remnant of the body that hit and broke up the L-chondrite parent body, creating one of the major asteroid families in the asteroid belt. After two decades of systematic recovery of fossil meteorites and relict extraterrestrial spinel grains from marine limestone, it appears that the meteorite flux to Earth in the mid-Ordovician was very different from that of today

Rare meteorites common in the Ordovician period

© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. Most meteorites that fall today are H and L type ordinary chondrites, yet the main belt asteroids best positioned to deliver meteorites are LL chondrites 1,2. This suggests that the current meteorite flux is dominated by fragments from recent asteroid breakup events 3,4 and therefore is not representative over longer (100-Myr) timescales. Here we present the first reconstruction of the composition of the background meteorite flux to Earth on such timescales. From limestone that formed about one million years before the breakup of the L-chondrite parent body 466 Myr ago, we have recovered relict minerals from coarse micrometeorites. By elemental and oxygen-isotopic analyses, we show that before 466 Myr ago, achondrites from different asteroidal sources had similar or higher abundances than ordinary chondrites. The primitive achondrites, such as lodranites and acapulcoites, together with related ungrouped achondrites, made up ∼15-34% of the flux compared with only ∼0.45% today. Another group of abundant achondrites may be linked to a 500-km cratering event on (4) Vesta that filled the inner main belt with basaltic fragments a billion years ago 5. Our data show that the meteorite flux has varied over geological time as asteroid disruptions create new fragment populations that then slowly fade away from collisional and dynamical evolution. The current flux favours disruption events that are larger, younger and/or highly efficient at delivering material to Earth

Managing Insect and Mite Pests of Texas Corn.

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Сенсибилизация к аллергенам клещей домашней пыли у детей

ДЫХАТЕЛЬНАЯ ГИПЕРЧУВСТВИТЕЛЬНОСТЬАЛЛЕРГОЗЫ РЕСПИРАТОРНЫЕГИПЕРСЕНСИБИЛИЗАЦИЯ РЕСПИРАТОРНАЯРЕСПИРАТОРНАЯ АЛЛЕРГИЯАЛЛЕРГЕНЫКЛЕЩИ ПЫЛЕВЫЕ ДОМАШНИЕDERMATOPHAGOIDES PTERONYSSINUSDERMATOPHAGOIDES FARINAEСЕНСИБИЛИЗАЦИЯ БИОЛОГИЧЕСКАЯСЕНСИБИЛИЗАЦИЯ К АЛЛЕРГЕНАМДЕТИОБЗОР ЛИТЕРАТУРЫАллергические заболевания представляют серьезную проблему современной медицины. Сенсибилизация к ингаляционным аллергенам является одним из ключевых факторов формирования респираторных аллергозов. Среди аэроаллергенов важное значение играют аллергенные компоненты домашней пыли – клещи Dermatophagoides pteronyssinus и Dermatophagoides farinae, составляющие до 90% акарофауны жилых помещений. В формировании сенсибилизации к клещам домашней пыли также предполагается роль индивидуальных источников аллергенов. Сенсибилизация к мажорным компонентам аллергена клещей домашней пыли ассоциируется с риском развития бронхиальной астмы, к минорным (Der p 10) – риском развития перекрестных реакций с тропомиозином других беспозвоночных, тропомиозином человека. Аллергены клещей домашней пыли (Der p 2 и Der f 2) могут быть ответственны за симптомы оральной клещевой анафилаксии, а также способствовать развитию сенсибилизации к бактериальным антигенам Staphylococcus aureus и Escherichia coli. В 1 части статьи изложены биология и источники клеща домашней пыли. Представлена классификация аллергенов, пути сенсибилизации и распространенность сенсибилизации к клещу домашней пыли у детей.Allergic diseases are a serious problem in modern medicine. Sensitization to inhalation allergens is one of the key factors in the formation of respiratory allergoses. Among aeroallergens, allergenic components of domestic dust play an important role – mites Dermatophagoides pteronyssinus and Dermatophagoides farinae, that make up to 90% of the acarofauna of residential premises. In the formation of sensitization to domestic dust mites, the role of individual sources of allergens is also considered. Sensitization to the major components of the domestic dust mite allergens is associated with the risk of developing bronchial asthma, to minor ones (Der p 10) – the risk of cross-reactions with tropomyosin of other invertebrates, human tropomyosin. Domestic dust mite allergens (Der p 2 and Der f 2) may be responsible for the symptoms of oral tick-born anaphylaxis as well as for the development of sensitization to bacterial antigens of Staphylococcus aureus and Escherichia coli. Part 1 of this article outlines biology and sources of the domestic dust mite. The classification of allergens, sensitization pathways and the prevalence of sensitization to domestic dust mite in children are presented