Meteoroid, Bolide and Meteorite «Chelyabinsk»

This paper presents the brief review of Chelyabinsk group of meteoroid, bolide and meteorite "Chelyabinsk" investigations. Height of the maximum of the main flash of Chelyabinsk bolide is 30 km. Only 1% of meteoroid mass arrived to the Earth surface in the form of meteorites while the most part of meteoroid became dust. During four days the dust had circumnavigated the globe and formed stratospheric dust belt. This new dust belt, located above the Junge aerosol layer, has persisted over at least a three-month period. The mass distribution of found meteorites is lognormal. This shape argues that fragmentation process of initial body happened randomly and in a cascade way. Transparent or translucent mineral filaments firmly linked to the particles were found in the meteoritic dust. In metallic phases of the meteorite mainly Fe-rich compounds exist. Very interesting topics of next research are magnetic properties of Fe-Ni phase, because of cosmic synthesis conditions. Meteoroids like "Chelyabinsk" fall on average once every 30 years. Therefore the problem of "asteroid and comet danger" should be expanded to the problem of "meteoroid, asteroid and comet danger".

Crises and extinction in the fossil record—a role for ultraviolet radiation?

A number of natural events can cause ozone depletion, including asteroid and comet impacts, large-scale volcanism involving the stratospheric injection of chlorine, and close cosmic events such as supernovae. These events have previously been postulated to have been sole or contributory causes of mass extinctions. Following such events, UV-B radiation would have been elevated at the surface of the earth. The possibilities for detecting elevated UV-B as a kill mechanism in the fossil record are discussed. In the case of impact events and large-scale volcanism, the taxa affected by increases in UV-B radiation are likely to be similar to those affected by cooling and by the initial drop in irradiance caused by stratospheric dust injection. Thus UV-B may synergistically exacerbate the effects of these other environmental changes and contribute to stress in the biosphere, although UV-B alone is unlikely to cause a mass extinction. By the same token, however, this similarity in affected taxa is likely to make delineating the involvement of UV-B radiation in the fossil record more difficult. Cosmic events such as supernovae may produce smaller extinction events, but ones that are “cleaner” UV catastrophes without the involvement of other environmental changes.

Climate-Volcanism Feedback and the Toba Eruption of ∼74,000 Years Ago

A general feedback between volcanism and climate at times of transition in the Quaternary climate record is suggested, exemplified by events accompanying the Toba eruption (∼74,000 yr ago), the largest known late Quaternary explosive volcanic eruption. The Toba paroxysm occurred during the δ18O stage 5a-4 transition, a period of rapid ice growth and falling global sea level, which may have been a factor in creating stresses that triggered the volcanic event. Toba is estimated to have produced between 1015 and 1016 g of fine ash and sulfur gases lofted in co-ignimbrite ash clouds to heights of at least 32 ± 5 km, which may have led to dense stratospheric dust and sulfuric acid aerosol clouds. These conditions could have created a brief, dramatic cooling or "volcanic winter," followed by estimated annual Northern Hemisphere surface-temperature decreases of ∼3° to 5°C caused by the longer-lived aerosols. Summer temperature decreases of ⩾10°C at high northern latitudes, adjacent to regions already covered by snow and ice, might have increased snow cover and sea-ice extent, accelerating the global cooling already in progress. Evidence for such climate-volcanic feedback, following Milankovitch periodicities, is found at several climatic transitions.