Decreases in the seawater ¹⁸⁷Os/¹⁸⁸Os ratio caused by the impact of a chondritic meteorite are indicative of projectile size, if the soluble fraction of osmium carried by the impacting body is known. ...Resulting diameter estimates of the Late Eocene and Cretaceous/Paleogene projectiles are within 50% of independent estimates derived from iridium data, assuming total vaporization and dissolution of osmium in seawater. The variations of ¹⁸⁷Os/¹⁸⁸Os and Os/Ir across the Late Eocene impact-event horizon support the main assumptions required to estimate the projectile diameter. Chondritic impacts as small as 2 kilometers in diameter should produce observable excursions in the marine osmium isotope record, suggesting that previously unrecognized impact events can be identified by this method.
The cause of the end-Cretaceous mass extinction is vigorously debated, owing to the occurrence of a very large bolide impact and flood basalt volcanism near the boundary. Disentangling their relative ...importance is complicated by uncertainty regarding kill mechanisms and the relative timing of volcanogenic outgassing, impact, and extinction. We used carbon cycle modeling and paleotemperature records to constrain the timing of volcanogenic outgassing. We found support for major outgassing beginning and ending distinctly before the impact, with only the impact coinciding with mass extinction and biologically amplified carbon cycle change. Our models show that these extinction-related carbon cycle changes would have allowed the ocean to absorb massive amounts of carbon dioxide, thus limiting the global warming otherwise expected from postextinction volcanism.
Anthropogenic activity has increased recent sediment concentrations of Pt and Pd in Boston Harbor by approximately 5 times background concentrations. Surface sediments and downcore profiles were ...investigated to evaluate Pt and Pd accumulation and behavior in urban coastal sediments. There is no clear correlation between temporal changes in Pt and Pd consumption and sediment concentration. However, Pt/Pb and Pd/Pb ratios suggest that Pt and Pd flux into the Harbor may not be decreasing with cessation of sludge input as rapidly as other metals. This is supported by the large discrepancy between fluxes associated with sludge and effluent release and those calculated from surface sediment concentrations. This evidence supports catalytic converters as a major source of Pd and Pt to Boston Harbor but cannot preclude other sources. Pd does not exhibit signs of post-burial remobilization below the mixed layer in the sediment cores, although near-surface variability in Pd concentrations may indicate a labile Pd component. Pt displays an inverse correlation with Mn above the oxic/suboxic transition, similar to behavior seen in pristine sediments where Pt is thought to be chemically mobile. This study does not support the use of Pd and Pt as tracers of recent contaminated sedimentation. However, the possibility of a labile Pt and Pd in these sediments highlights the need for further study of the biological uptake of these metals.
Morgan argues that excursions in the marine Os record are of little value for estimating impactor size. This claim is based on computer simulations of the formation of the Chicxulub crater and ...distribution of the ejecta, which are difficult to validate. More important, by narrowly focusing on the Cretaceous-Tertiary event Morgan's comment misses the broader implications of our study.
High resolution records (ca. 100 kyr) of Os isotope composition (
187Os
/
188Os) in bulk sediments from two tropical Pacific sites (ODP Sites 1218 and 1219) capture the complete Late Eocene
187Os
/
...188Os excursion and confirm that the Late Eocene
187Os
/
188Os minimum, earlier reported by Ravizza and Peucker-Ehrenbrink Earth Planet. Sci. Lett. 210 (2003) 151–165, is a global feature. Using the astronomically tuned age models available for these sites, it is suggested that the Late Eocene
187Os
/
188Os minimum can be placed at 34.5
±
0.1 Ma in the marine records. In addition, two other distinct features of the
187Os
/
188Os excursion that are correlatable among sections are proposed as chemostratigraphic markers which can serve as age control points with a precision of ca. ±
0.1 Myr. We propose a speculative hypothesis that higher cosmic dust flux in the Late Eocene may have contributed to global cooling and Early Oligocene glaciation (Oi-1) by supplying bio-essential trace elements to the oceans and thereby resulting in higher ocean productivity, enhanced burial of organic carbon and draw down of atmospheric CO
2. To determine if the hypothesis that enhanced cosmic dust flux in the Late Eocene was a cause for the
187Os
/
188Os excursion can be tested by using the paired bulk sediment and leachate Os isotope composition;
187Os
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188Os were also measured in sediment leachates. Results of analyses of leachates are inconsistent between the south Atlantic and the Pacific sites, and therefore do not yield a robust test of this hypothesis. Comparison of
187Os
/
188Os records with high resolution benthic foraminiferal
δ
18O records across the Eocene–Oligocene transition suggests that
187Os flux to the oceans decreased during cooling and ice growth leading to the Oi-1 glaciation, whereas subsequent decay of ice-sheets and deglacial weathering drove seawater
187Os
/
188Os to higher values. Although the precise timing and magnitude of these changes in weathering fluxes and their effects on the marine
187Os
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188Os records are obscured by recovery from the Late Eocene
187Os
/
188Os excursion, evidence of the global influence of glaciation on supply of Os to the ocean is robust as it has now been documented in both Pacific and Atlantic records.
Abstract
The “Search for life”, which may be extinct or extant on other planetary bodies is one of the major goals of NASA planetary exploration missions. Finding such evidence of biological residue ...in a vast planetary landscape is an enormous challenge. We have developed a highly sensitive instrument, the “Compact Color Biofinder”, which can locate minute amounts of biological material in a large area at video speed from a standoff distance. Here we demonstrate the efficacy of the Biofinder to detect fossils that still possess strong bio-fluorescence signals from a collection of samples. Fluorescence images taken by the Biofinder instrument show that all
Knightia
spp. fish fossils analysed from the Green River formation (Eocene, 56.0–33.9 Mya) still contain considerable amounts of biological residues. The biofluorescence images support the fact that organic matter has been well preserved in the Green River formation, and thus, not diagenetically replaced (replaced by minerals) over such a significant timescale. We further corroborated results from the Biofinder fluorescence imagery through Raman and attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopies, scanning electron microscopy, energy dispersive X-ray spectroscopy (SEM–EDS), and fluorescence lifetime imaging microscopy (FLIM). Our findings confirm once more that biological residues can survive millions of years, and that using biofluorescence imaging effectively detects these trace residues in real time. We anticipate that fluorescence imaging will be critical in future NASA missions to detect organics and the existence of life on other planetary bodies.
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