Recent research indicates that more oxygen exists in the core of Earth than had been originally thought. Livermore geologist Rick Ryerson and colleagues in England, France, and Switzerland have made new findings about the origin of Earth by considering the geophysical and geochemical signatures of its core and mantle together. Based on the higher oxygen concentration of the core, the team concluded that Earth must have accreted material more oxidized than the present-day mantle—material similar to that found in some asteroids and in planetesimals, small bodies formed of dust and rock. In the image—courtesy of France’s Institut de Physique du Globe de Paris—a model shows planetesimals accreting to a growing Earth.
Earth formed about 4.56 billion years ago, over several tens of millions of years, by accreting these planetesimals and planetary embryos. Progressively larger impacts delivered energy that maintained Earth’s outer layer and an extensively molten magma ocean. Gravitational separation of metal and silicate within the magma ocean resulted in a metallic core and a silicate mantle.
Earth’s core’s formation left behind geophysical and geochemical signatures that remain to this day. In the past, formation models addressed the evolution of core and mantle compositional signatures separately, rather than jointly. The team found that core formation occurred in a hot, liquid, moderately deep magma ocean not exceeding 1,800 kilometers in depth, under conditions more oxidized than present-day Earth. Oxygen concentrations were higher and silicon lower than previous estimates. “This new model is at odds with the current belief that core formation occurred under reduction conditions,” Ryerson says. “Instead, we found that Earth’s magma ocean started out oxidized and has become reduced through time by oxygen incorporation into the core.”
Contact: Rick Ryerson (925) 422-6170 (ryerson1@llnl.gov).
The smallest electronics—nanoelectric devices—could one day have the ability to turn on and off at an atomic scale thanks to the work of Lawrence Livermore scientists. They have investigated the synthesis of linear chains of carbon atoms from laser-melted graphite into a material called carbyne. Found occurring naturally in meteorites, this unusual form of carbon could have the ability to adjust the level of electrical current traveling through a circuit depending on the user’s needs, as well as other useful electrical properties, thanks to its sensitivity to stretching and bending. Carbyne is also 40 times stiffer than diamond, making it potentially useful in superhard materials.
Livermore scientist Nir Goldman and Caltech undergraduate researcher Christopher Cannella were studying the evaporative properties of liquid carbon using computer simulation. They simulated the laser-based heating of graphite to several thousand degrees to form a volatile droplet. To their surprise, as the liquid droplet evaporated and cooled, it formed bundles of linear chains of carbon atoms. “There’s been a lot of speculation about how to make carbyne and how stable it is,” Goldman says. “We showed that laser melting of graphite is one viable avenue for its synthesis. Carbyne could have applications as a new material in a number of areas, including as a tunable semiconductor or even in hydrogen storage.”
“The process also could occur in astrophysical bodies or the interstellar medium, where carbon-containing material can be exposed to relatively high temperatures and carbon can liquefy,” he adds.
Contact: Nir Goldman (925) 422-3994 (goldman14@llnl.gov).
Livermore scientists have developed a theory of why dark matter has evaded direct detection in Earth-based experiments. A group of U.S. particle physicists known as the Lattice Strong Dynamics Collaboration, led by a Livermore team, combined theoretical and computational physics techniques and used the Laboratory’s massively parallel Vulcan supercomputer to devise a new model of dark matter. The team’s work indicates that although naturally “stealthy” today, dark matter would have been easy to see by way of interactions with ordinary matter in the extremely high-temperature plasma conditions that pervaded the early universe.
“These interactions are important because ordinary and dark matter abundances today are strikingly similar in size, suggesting a balancing act occurring between the two before the universe cooled,” says team leader Pavlos Vranas.
Dark matter comprises 83 percent of all matter in the universe but does not interact directly with the electromagnetic, strong, or weak nuclear forces. Although essentially invisible, dark matter’s interactions with gravity affect the movement of galaxies, leaving little doubt of its existence. The team’s research suggests the key to stealth dark matter’s split personality is its compositeness and confinement. Like quarks in a neutron, dark matter’s electrically charged constituents interact with nearly everything at high temperatures. At lower temperatures, however, they bind together to form an electrically neutral composite particle. Unlike a neutron bound by the ordinary strong interaction of quantum chromodynamics (QCD), the stealthy neutron would have to be bound by a new, unobserved strong interaction, a dark form of QCD.
“Underground direct detection experiments or experiments at the Large Hadron Collider may soon find evidence of, or rule out, this new stealth dark matter theory,” Vranas explains.
Contact: Pavlos Vranas (925) 422-4681 (vranas2@llnl.gov).
Lawrence Livermore researchers have found that nanocrystalline materials do not necessarily resist the effects of radiation in nuclear reactors better than currently used materials. For years, simulations had shown that nanocrystals would not only absorb radiation damage better than the polycrystalline materials used in nuclear reactors today but would also be functional at the elevated temperatures in those reactors.
However, experimental research previously published in Applied Physics Letters by Livermore’s Mukul Kumar and colleagues showed that nanocrystalline materials have poor stability under the thermal conditions in reactors. In new research published in the September 1, 2015, edition of the journal Acta Materialia, Kumar’s team, through extensive in situ high-voltage transmission electron microscopy, discovered that the nanocrystalline materials do not survive radiation damage, either.
Most structural materials used in nuclear reactors are prone to radiation damage that degrades their mechanical properties and limits their service life. The team theorized that a high-density grain boundary area would act as an effective sink for radiation-induced defects. However, continued absorption of defects can alter the structure of grain boundaries or enhance their mobility, eventually leading to microstructural degradation, thus negating their initial radiation tolerance. The final results showed the nanocrystals did not survive radiation damage better than currently used materials.
Kumar says a new kind of grain boundary network could be engineered in polycrystalline microstructures that might better withstand high temperatures, resist radiation damage, and extend the lifetime of reactor components. Such a network would comprise a mix of low-energy boundaries to resist thermal coarsening and high-energy boundaries to absorb the defects.
Contact: Mukul Kumar (925) 422-0600 (kumar3@llnl.gov).
In a paper appearing in the September 8, 2015, online edition of Proceedings of the National Academy of Sciences, a multi-institutional team of researchers showed that long-term leaf litter decomposition rates in forest ecosystems are tightly coupled to manganese reduction and oxidation (redox) cycling. Over seven years of litter decomposition, the observed microbial transformation of litter was found to be strongly correlated to variations in manganese oxidation state and concentration.
The team’s results suggest that the litter-decomposing mechanisms in the coniferous forest site they studied depend on the ability of plants and microbes to supply, accumulate, and regenerate short-lived manganese ions in the litter layer. This implies that the bioavailability, mobility, and reactivity of the elements in the plant–soil system have a profound effect on litter decomposition rates and therefore on the planet’s overall carbon cycle.
The decomposition of plant litter is a fundamental property of ecosystems that also controls nutrient cycling and various soil properties, including productivity. Traditional models assume that decomposition rates are controlled by a more broadly defined litter “quality,” encompassing parameters such as lignin content as predictor variables.
Contact: Jennifer Pett-Ridge (925) 424-2882 (pettridge2@llnl.gov).
Astronomers have found evidence of a faded electron cloud that is “coming back to life” in the wake of a collision of two galaxy clusters. This “radio phoenix,” so-called because its high-energy electrons radiate primarily at radio frequencies, is found in Abell 1033, located approximately 1.6 billion light years from Earth. The research appears in a recent issue of the Monthly Notices of the Royal Astronomical Society.
Galaxy clusters, the largest structures in the universe held together by gravity, contain hundreds or even thousands of individual galaxies, unseen dark matter, and huge reservoirs of hot gas. Understanding how these clusters grow is key to tracking how the universe evolves over time. By combining data from NASA’s Chandra X-Ray Observatory, the Westerbork Synthesis Radio Telescope in the Netherlands, the National Science Foundation’s Karl Jansky Very Large Array, and the Sloan Digital Sky Survey, Livermore scientist Will Dawson and others were able to re-create the cosmic story of the radio phoenix.
Dawson mapped galaxy distributions and analyzed merger dynamics. The team’s results suggest that the supermassive black hole near the center of Abell 1033 erupted in the past, sending high-energy electrons throughout a region hundreds of thousands of light years across and producing a cloud of bright radio emission. Over millions of years, this cloud faded as the electrons lost energy and the cloud expanded. However, when a plasma shock from the galaxy cluster collision passed through this cloud, electrons were reaccelerated, giving rise to the radio phoenix.
Contact: Will Dawson (925) 424-3732 (dawson29@llnl.gov).