Very large collisions in the asteroid belt could lead temporarily to a substantial increase in th... more Very large collisions in the asteroid belt could lead temporarily to a substantial increase in the rate of impacts of meteorites on Earth. Orbital simulations predict that fragments from such events may arrive considerably faster than the typical transit times of meteorites falling today, because in some large impacts part of the debris is transferred directly into a resonant orbit with Jupiter. Such an efficient meteorite delivery track, however, has not been verified. Here we report high-sensitivity measurements of noble gases produced by cosmic rays in chromite grains from a unique suite of fossil meteorites preserved in approximately 480 million year old sediments. The transfer times deduced from the noble gases are as short as approximately 10(5) years, and they increase with stratigraphic height in agreement with the estimated duration of sedimentation. These data provide powerful evidence that this unusual meteorite occurrence was the result of a long-lasting rain of meteorit...
We are using atom-probe tomography to clarify the origin of meteoritic nanodiamonds. We report ne... more We are using atom-probe tomography to clarify the origin of meteoritic nanodiamonds. We report new data and revised analytical protocols in our continuing efforts to quantitatively determine the C-isotopic ratios of individual ~3 nm nanodiamonds.
ABSTRACT Dead time effects in time-of-flight secondary ion mass spectrometry are well known and c... more ABSTRACT Dead time effects in time-of-flight secondary ion mass spectrometry are well known and can be corrected for using Poisson statistics. Laser-induced desorption, however, introduces nonlinearity in the evaporation process resulting in highly fluctuating signals that make proper dead time correction much more challenging. Here, we propose a modified dead time correction procedure that overcomes such obstacles using data from correlated detection events from different isotopes of a single element. Provided the signals are not affected by unresolved mass interferences, this dead time correction enables us to obtain meaningful isotope ratios as demonstrated for atom probe tomography data of carbon from nanodiamonds and of silicon.
We present new data from the novel application of atom-probe tomography to the study of nanodiamo... more We present new data from the novel application of atom-probe tomography to the study of nanodiamonds from the meteorite Allende. The mean meteoritic ^12C/^13C peak ratio is higher than that of our standards, but there are instrumental artifacts.
Atom-probe tomography is an analytical method that has considerable potential in cosmochemistry. ... more Atom-probe tomography is an analytical method that has considerable potential in cosmochemistry. We summarize results from nanodiamonds and presolar SiC.
ABSTRACT We show new Al-Mg data from a search for FUN CAIs by LA-MC-ICP-MS. We observe a wide ran... more ABSTRACT We show new Al-Mg data from a search for FUN CAIs by LA-MC-ICP-MS. We observe a wide range in stable-isotope fractionation between and within different CAIs.
ABSTRACT We quantify abundances and elemental compositions of acid-resistant minerals in unequili... more ABSTRACT We quantify abundances and elemental compositions of acid-resistant minerals in unequilibrated L chondrite Mezö-Madaras. The results from this study will serve as a proxy to classify extraterrestrial minerals found in sediments and fossil meteorites.
Very large collisions in the asteroid belt could lead temporarily to a substantial increase in th... more Very large collisions in the asteroid belt could lead temporarily to a substantial increase in the rate of impacts of meteorites on Earth. Orbital simulations predict that fragments from such events may arrive considerably faster than the typical transit times of meteorites falling today, because in some large impacts part of the debris is transferred directly into a resonant orbit with Jupiter. Such an efficient meteorite delivery track, however, has not been verified. Here we report high-sensitivity measurements of noble gases produced by cosmic rays in chromite grains from a unique suite of fossil meteorites preserved in approximately 480 million year old sediments. The transfer times deduced from the noble gases are as short as approximately 10(5) years, and they increase with stratigraphic height in agreement with the estimated duration of sedimentation. These data provide powerful evidence that this unusual meteorite occurrence was the result of a long-lasting rain of meteorit...
We are using atom-probe tomography to clarify the origin of meteoritic nanodiamonds. We report ne... more We are using atom-probe tomography to clarify the origin of meteoritic nanodiamonds. We report new data and revised analytical protocols in our continuing efforts to quantitatively determine the C-isotopic ratios of individual ~3 nm nanodiamonds.
ABSTRACT Dead time effects in time-of-flight secondary ion mass spectrometry are well known and c... more ABSTRACT Dead time effects in time-of-flight secondary ion mass spectrometry are well known and can be corrected for using Poisson statistics. Laser-induced desorption, however, introduces nonlinearity in the evaporation process resulting in highly fluctuating signals that make proper dead time correction much more challenging. Here, we propose a modified dead time correction procedure that overcomes such obstacles using data from correlated detection events from different isotopes of a single element. Provided the signals are not affected by unresolved mass interferences, this dead time correction enables us to obtain meaningful isotope ratios as demonstrated for atom probe tomography data of carbon from nanodiamonds and of silicon.
We present new data from the novel application of atom-probe tomography to the study of nanodiamo... more We present new data from the novel application of atom-probe tomography to the study of nanodiamonds from the meteorite Allende. The mean meteoritic ^12C/^13C peak ratio is higher than that of our standards, but there are instrumental artifacts.
Atom-probe tomography is an analytical method that has considerable potential in cosmochemistry. ... more Atom-probe tomography is an analytical method that has considerable potential in cosmochemistry. We summarize results from nanodiamonds and presolar SiC.
ABSTRACT We show new Al-Mg data from a search for FUN CAIs by LA-MC-ICP-MS. We observe a wide ran... more ABSTRACT We show new Al-Mg data from a search for FUN CAIs by LA-MC-ICP-MS. We observe a wide range in stable-isotope fractionation between and within different CAIs.
ABSTRACT We quantify abundances and elemental compositions of acid-resistant minerals in unequili... more ABSTRACT We quantify abundances and elemental compositions of acid-resistant minerals in unequilibrated L chondrite Mezö-Madaras. The results from this study will serve as a proxy to classify extraterrestrial minerals found in sediments and fossil meteorites.
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