The parent body of the ca. 480 kyr-old Tunguska-like impact over Antarctica.

第2回極域科学シンポジウム/第34回南極隕石シンポジウム 11月17日（木） 国立国語研究所 2階講

Preservation and detectability of shock-induced magnetization

An understanding of the effects of hypervelocity impacts on the magnetization of natural samples is required for interpreting paleomagnetic records of meteorites, lunar rocks, and cratered planetary surfaces. Rocks containing ferromagnetic minerals have been shown to acquire shock remanent magnetization (SRM) due to the passage of a shock wave in the presence of an ambient magnetic field. In this study, we conducted pressure remanent magnetization (PRM) acquisition experiments on a variety of natural samples as an analog for SRM acquisition at pressures ranging up to 1.8 GPa. Comparison of the alternating field (AF) and thermal demagnetization behavior of PRM confirms that AF demagnetization is a more efficient method for removing SRM overprints than thermal demagnetization because SRM may persist to unblocking temperatures approaching the Curie temperatures of magnetic minerals. The blocking of SRM to high temperatures suggests that SRM could persist without being eradicated by viscous relaxation over geologic timescales. However, SRM has been rarely observed in natural samples likely because of two factors: (1) other forms of impact-related remanence (e.g., thermal remanent magnetization from impact-related heating or chemical remanent magnetization from postimpact hydrothermal activity) are often acquired by target rocks that overprint SRM, and (2) low SRM acquisition efficiencies may prevent SRM from being distinguished from the underlying primary remanence or other overprints due to its low magnetization intensity

Controlled-atmosphere thermal demagnetization and paleointensity analyses of extraterrestrial rocks

We describe a system for conducting thermal demagnetization of extraterrestrial rocks in a controlled atmosphere appropriate for a wide range of oxygen fugacities within the stability domain of iron. Thermal demagnetization and Thellier-Thellier paleointensity experiments on lunar basalt synthetic analogs show that the controlled atmosphere prevents oxidation of magnetic carriers. When combined with multidomain paleointensity techniques, this opens the possibility of highly accurate thermal demagnetization and paleointensity measurements on rocks from the Moon and asteroids.United States. National Aeronautics and Space Administration (Grant NNX12AH80G)

Paleomagnetism. Solar nebula magnetic fields recorded in the Semarkona meteorite.

Magnetic fields are proposed to have played a critical role in some of the most enigmatic processes of planetary formation by mediating the rapid accretion of disk material onto the central star and the formation of the first solids. However, there have been no experimental constraints on the intensity of these fields. Here we show that dusty olivine-bearing chondrules from the Semarkona meteorite were magnetized in a nebular field of 54 ± 21 microteslas. This intensity supports chondrule formation by nebular shocks or planetesimal collisions rather than by electric currents, the x-wind, or other mechanisms near the Sun. This implies that background magnetic fields in the terrestrial planet-forming region were likely 5 to 54 microteslas, which is sufficient to account for measured rates of mass and angular momentum transport in protoplanetary disks.This is the accepted manuscript. The final version is available from Science at http://www.sciencemag.org/content/346/6213/1089.abstract

Linking global drivers of agricultural trade to on-the-ground impacts on biodiversity.

Consumption of globally traded agricultural commodities like soy and palm oil is one of the primary causes of deforestation and biodiversity loss in some of the world's most species-rich ecosystems. However, the complexity of global supply chains has confounded efforts to reduce impacts. Companies and governments with sustainability commitments struggle to understand their own sourcing patterns, while the activities of more unscrupulous actors are conveniently masked by the opacity of global trade. We combine state-of-the-art material flow, economic trade, and biodiversity impact models to produce an innovative approach for understanding the impacts of trade on biodiversity loss and the roles of remote markets and actors. We do this for the production of soy in the Brazilian Cerrado, home to more than 5% of the world´s species. Distinct sourcing patterns of consumer countries and trading companies result in substantially different impacts on endemic species. Connections between individual buyers and specific hot spots explain the disproportionate impacts of some actors on endemic species and individual threatened species, such as the particular impact of European Union consumers on the recent habitat losses for the iconic giant anteater (Myrmecophaga tridactyla). In making these linkages explicit, our approach enables commodity buyers and investors to target their efforts much more closely to improve the sustainability of their supply chains in their sourcing regions while also transforming our ability to monitor the impact of such commitments over time.UK Global Food Security programme (Project 304 BB/N02060X/1

Using supply chain data to monitor zero deforestation commitments: an assessment of progress in the Brazilian soy sector

Zero deforestation commitments (ZDCs) are voluntary initiatives where companies or countries pledge to eliminate deforestation from their supply chains. These commitments offer much promise for sustainable commodity production, but are undermined by a lack of transparency about their coverage and impacts. Here, using state-of-the-art supply chain data, we introduce an approach to evaluate the impact of ZDCs, linking traders and international markets to commodity-associated deforestation in the sub-national jurisdictions from which they source. We focus on the Brazilian soy sector, where we find that ZDC coverage is increasing, but under-represents the Cerrado biome where most soy-associated deforestation currently takes place. Though soy-associated deforestation declined in the Amazon after the introduction of the Soy Moratorium, we observe no change in the exposure of companies or countries adopting ZDCs to soy-associated deforestation in the Cerrado. We further assess the formulation and implementation of these ZDCs and identify several systematic weaknesses that must be addressed to increase the likelihood that they achieve meaningful reductions in deforestation in future. As the 2020 deadline for several of these commitments approaches, our approach can provide independent monitoring of progress toward the goal of ending commodity-associated deforestation