Luann Becker

Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling

A carbon-rich black layer, dating to ≈12.9 ka, has been previously identified at ≈50 Clovis-age sites across North America and appears contemporaneous with the abrupt onset of Younger Dryas (YD) cooling. The in situ bones of extinct Pleistocene megafauna, along with Clovis tool assemblages, occur below this black layer but not within or above it. Causes for the extinctions, YD cooling, and termination of Clovis culture have long been controversial. In this paper, we provide evidence for an extraterrestrial (ET) impact event at ≅12.9 ka, which we hypothesize caused abrupt environmental changes that contributed to YD cooling, major ecological reorganization, broad-scale extinctions, and rapid human behavioral shifts at the end of the Clovis Period. Clovis-age sites in North American are overlain by a thin, discrete layer with varying peak abundances of (i) magnetic grains with iridium, (ii) magnetic microspherules, (iii) charcoal, (iv) soot, (v) carbon spherules, (vi) glass-like carbon containing nanodiamonds, and (vii) fullerenes with ET helium, all of which are evidence for an ET impact and associated biomass burning at ≈12.9 ka. This layer also extends throughout at least 15 Carolina Bays, which are unique, elliptical depressions, oriented to the northwest across the Atlantic Coastal Plain. We propose that one or more large, low-density ET objects exploded over northern North America, partially destabilizing the Laurentide Ice Sheet and triggering YD cooling. The shock wave, thermal pulse, and event-related environmental effects (e.g., extensive biomass burning and food limitations) contributed to end-Pleistocene megafaunal extinctions and adaptive shifts among PaleoAmericans in North America.

Extraterrestrial helium trapped in fullerenes in the Sudbury impact structure.

Fullerenes (C60 and C70) in the Sudbury impact structure contain trapped helium with a 3He/4He ratio of 5.5 × 10−4 to 5.9 × 10−4. The 3He/4He ratio exceeds the accepted solar wind value by 20 to 30 percent and is higher by an order of magnitude than the maximum reported mantle value. Terrestrial nuclear reactions or cosmic-ray bombardment are not sufficient to generate such a high ratio. The 3He/4He ratios in the Sudbury fullerenes are similar to those found in meteorites and in some interplanetary dust particles. The implication is that the helium within the C60 molecules at Sudbury is of extraterrestrial origin.

Fullerenes and interplanetary dust at the Permian-Triassic boundary.

We recently presented new evidence that an impact occurred approximately 250 million years ago at the Permian-Triassic boundary (PTB), triggering the most severe mass extinction in the history of life on Earth. We used a new extraterrestrial tracer, fullerene, a third carbon carrier of noble gases besides diamond and graphite. By exploiting the unique properties of this molecule to trap noble gases inside of its caged structure (helium, neon, argon), the origin of the fullerenes can be determined. Here, we present new evidence for fullerenes with extraterrestrial noble gases in the PTB at Graphite Peak, Antarctica, similar to PTB fullerenes from Meishan, China and Sasayama, Japan. In addition, we isolated a (3)He-rich magnetic carrier phase in three fractions from the Graphite Peak section. The noble gases in this magnetic fraction were similar to zero-age deep-sea interplanetary dust particles (IDPs) and some magnetic grains isolated from the Cretaceous-Tertiary boundary. The helium and neon isotopic compositions for both the bulk Graphite Peak sediments and an isolated magnetic fraction from the bulk material are consistent with solar-type gases measured in zero-age deep-sea sediments and point to a common source, namely, the flux of IDPs to the Earths surface. In this instance, the IDP noble gas signature for the bulk sediment can be uniquely decoupled from fullerene, demonstrating that two separate tracers are present (direct flux of IDPs for (3)He vs. giant impact for fullerene).

The origin of organic matter in the Martian meteorite ALH84001

Stable carbon isotope measurements of the organic matter associated with the carbonate globules and the bulk matrix material in the ALH84001 Martian meteorite indicate that two distinct sources are present in the sample. The delta 13C values for the organic matter associated with the carbonate globules averaged -26% and is attributed to terrestrial contamination. In contrast, the delta 13C values for the organic matter associated with the bulk matrix material yielded a value of -15%. The only common sources of carbon on the Earth that yield similar delta 13C values, other then some diagenetically altered marine carbonates, are C4 plants. A delta 13C value of -15%, on the other hand, is consistent with a kerogen-like component, the most ubiquitous form of organic matter found in carbonaceous chondrites such as the Murchison meteorite. Examination of the carbonate globules and bulk matrix material using laser desorption mass spectrometry (LDMS) indicates the presence of a high molecular weight organic component which appears to be extraterrestrial in origin, possibly derived from the exogenous delivery, of meteoritic or cometary debris to the surface of Mars.

The sonoluminescence spectrum of seawater

Abstract The sonoluminescence spectra of seawater and of a sodium chloride solution were determined by irradiation with ultrasound at 20 kHz. Ultrasound creates sonoluminescence through the process of acoustic cavitation: the formation, growth and implosive collapse of bubbles in a liquid. The sonoluminescence spectra of both seawater and NaCl in water are characterized by an emission line at 589 nm from excited-state sodium. Excited-state Na atoms are produced from the reaction of Na + with high-energy hydroxyl radicals formed directly during the cavitation event. Emission at 589 nm could be useful in determining whether sonochemical processes associated with cavitation occur in breaking waves or other turbulent flows.

Polycyclic aromatic hydrocarbons (PAHs) in Antarctic Martian meteorites, carbonaceous chondrites, and polar ice

Recent analyses of the carbonate globules present in the Martian meteorite ALH84001 have detected polycyclic aromatic hydrocarbons (PAHs) at the ppm level. The distribution of PAHs observed in ALH84001 was interpreted as being inconsistent with a terrestrial origin and were claimed to be indigenous to the meteorite, perhaps derived from an ancient martian biota. We have examined PAHs in the Antarctic shergottite EETA79001, which is also considered to be from Mars, as well as several Antarctic carbonaceous chondrites. We have found that many of the same PAHs detected in the ALH84001 carbonate globules are present in Antarctic carbonaceous chondrites and in both the matrix and carbonate (druse) component of EETA79001. We also investigated PAHs in polar ice and found that carbonate is an effective scavenger of PAHs in ice meltwater. Moreover, the distribution of PAHs in the carbonate extract of Antarctic Allan Hills ice is remarkably similar to that found in both EETA79001 and ALH84001. The reported presence of L-amino acids of apparent terrestrial origin in the EETA79001 druse material suggests that this meteorite is contaminated with terrestrial organics probably derived from Antarctic ice meltwater that had percolated through the meteorite. Our data suggests that the PAHs observed in both ALH84001 and EETA79001 are derived from either the exogenous delivery of organics to Mars or extraterrestrial and terrestrial PAHs present in the ice meltwater or, more likely, from a mixture of these sources. It would appear that PAHs are not useful biomarkers in the search for extinct or extant life in Mars.

For which compounds do we search in extraterrestrial samples for evidence of abiotic and/or biotic chemistry?

Any strategy for investigating whether abiotic and/or biotic organic molecules are present on planetary bodies in the solar system should focus on compounds which are readily synthesized under plausible prebiotic conditions, play an essential role in biochemistry as we know it and have properties such as chirality (handedness) which can be used to distinguish between abiotic vs. biotic origins. Amino acids are one of the few compound classes that fulfill all these requirements. They are synthesized in high yields in prebiotic simulation experiments, are one of the more abundant types of organic compounds present in carbonaceous meteorites and only the L-enantiomers are used in the proteins and enzymes in life on Earth. In contrast, polycylic aromatic hydrocarbons which have recently been detected in some Martian meteorites, have no role in biochemistry on Earth, and their molecular architecture, with the possible exception of the stable isotope composition, cannot be used to determine whether they were produced by biotic or abiotic processes. Recent results indicate that amino acids and their amine decomposition products can be directly isolated from samples using sublimation (450 degree(s) to 750 degree(s)C) under partial vacuum, thus eliminating the use of the aqueous reagents commonly used in the laboratory-based isolation of amino acids. A relatively new technology which shows promise for spacecraft-based amino acid analysis is microchip-based capillary electrophoresis. The actual separation hardware, including buffer reservoirs and derivatization reaction chambers, can be etched onto glass microchips with dimensions on the order of cm. This methodology offers the best potential for a compact, rugged, low-mass instrument package for in situ amino acid analyses during future space missions to Mars, Europa and comets.

Proof of exogenous delivery of organics to the early Earth in the sudbury impact structure

Fullerenes (C60 and C70 ) have recently been identified in a shock-produced breccia (Onaping Formation) associated with the 1.85 billion-year-old Sudbury Impact Structure (Becker et. al., 1994). The presence of one to ten ppm of fullerenes in this impact structure raises many questions about the origin of fullerenes, and the potential for delivery of intact organic material to the Earth by a large bolide (for example, an asteroid or comet). Because the Sudbury target rocks are carbon-poor, we previously suggested that the fullerene carbon was extraterrestrial in origin (Becker et. al., 1994). Two possible scenarios for the presence of fullerenes in the Sudbury impact deposits are: (i) That fullerenes are synthesized within the impact plume from the carbon contained in the bolide; or (ii) that fullerenes were already present in the bolide and survived the impact event. We have examined these possible sources of the Sudbury fullerenes by searching for noble gases trapped inside the fullerene molecule. The Sudbury fullerenes contain trapped helium with a 3He/4He ratio of 5.5 x 10 -4 to 5.9 x 10 -4. The 3He/4He ratio exceeds the accepted solar value by 20 to 30% and is an order of magnitude higher than the maximum reported mantle value. The 3He/4He ratios in the Sudbury fullerenes are similar to those found in meteorites and in some interplanetary dust particles. In addition, the 3He partial pressure for the Sudbury fullerenes at the time of formation is estimated to have been approximately 0.5 torr (vs. 10 -10 torr in the present day atmosphere) suggesting that a mechanism other then a terrestrial synthesis is needed The implication is that the helium within the C60 molecules at Sudbury is of extraterrestrial origin. The possibility that fullerenes containing extraterrestrial He, survived the impact at Sudbury has several interesting implications. First, other extraterrestrial organics may survive an impact event (Zaho and Bada, 1989) and thus the delivery of exogenous organics to the early Earth could have contributed to the prebiotic soup considered necessary for the origin of life. Second, the survival of C60 contradicts impact models and experiments that predict essentially complete vaporization of the bolide and destruction of all organic molecules (Chyba and Sagan, 1992). If this is the case, then current models and experiments for understanding the delivery and survivability of organics to the early Earth may need to be re-examined.