Nanodiamonds are forever: Did comet collision leave layer of nanodiamonds across Earth?

Date:

August 27, 2014

Source:

University of California - Santa Barbara

Summary:

A group of scientists, including UC Santa Barbara's James Kennett, professor emeritus in the Department of Earth Science, posited that a comet collision with Earth played a major role in the extinction. Their hypothesis suggests that a cosmic-impact event precipitated the Younger Dryas period of global cooling close to 12,800 years ago. This cosmic impact caused abrupt environmental stress and degradation that contributed to the extinction of most large animal species then inhabiting the Americas. According to Kennett, the catastrophic impact and the subsequent climate change also led to the disappearance of the prehistoric Clovis culture, known for its big game hunting, and to human population decline.in a new study published this week in the Journal of Geology, Kennett and an international group of scientists have focused on the character and distribution of nanodiamonds, one type of material produced during such an extraterrestrial collision. The researchers found an abundance of these tiny diamonds distributed over 50 million square kilometers across the Northern Hemisphere at the Younger Dryas boundary (YDB). This thin, carbon-rich layer is often visible as a thin black line a few meters below the surface

Kennett and investigators from 21 universities in six countries investigated nanodiamonds at 32 sites in 11 countries across North America, Europe and the Middle East. Two of the sites are just across the Santa Barbara Channel from UCSB: one at Arlington Canyon on Santa Rosa Island, the other at Daisy Cave on San Miguel Island."We conclusively have identified a thin layer over three continents, particularly in North America and Western Europe, that contain a rich assemblage of nanodiamonds, the production of which can be explained only by cosmic impact," Kennett said. "We have also found YDB glassy and metallic materials formed at temperatures in excess of 2200 degrees Celsius, which could not have resulted from wildfires, volcanism or meteoritic flux, but only from cosmic impact."

Most of North America's megafauna -- mastodons, short-faced bears, giant ground sloths, saber-toothed cats and American camels and horses -- disappeared close to 13,000 years ago at the end of the Pleistocene period. The cause of this massive extinction has long been debated by scientists who, until recently, could only speculate as to why.

The team found that the YDB layer also contained larger than normal amounts of cosmic impact spherules, high-temperature melt-glass, grapelike soot clusters, charcoal, carbon spherules, osmium, platinum and other materials. But in this paper the researchers focused their multi-analytical approach exclusively on nanodiamonds, which were found in several forms, including cubic (the form of diamonds used in jewelry) and hexagonal crystals.

"Different types of diamonds are found in the YDB assemblages because they are produced as a result of large variations in temperature, pressure and oxygen levels associated with the chaos of an impact," Kennett explained. "These are exotic conditions that came together to produce the diamonds from terrestrial carbon; the diamonds did not arrive with the incoming meteorite or comet."

Based on multiple analytical procedures, the researchers determined that the majority of the materials in the YDB samples are nanodiamonds and not some other kinds of minerals. The analysis showed that the nanodiamonds consistently occur in the YDB layer over broad areas.

"There is no known limit to the YDB strewnfield which currently covers more than 10 percent of the planet, indicating that the YDB event was a major cosmic impact," Kennett said. "The nanodiamond datum recognized in this study gives scientists a snapshot of a moment in time called an isochron."

To date, scientists know of only two layers in which more than one identification of nanodiamonds has been found: the YDB 12,800 years ago and the well-known Cretaceous-Tertiary boundary 65 million years ago, which is marked by the mass extinction of the dinosaurs, ammonites and many other groups.

"The evidence we present settles the debate about the existence of abundant YDB nanodiamonds," Kennett said. "Our hypothesis challenges some existing paradigms within several disciplines, including impact dynamics, archaeology, paleontology and paleoceanography/paleoclimatology, all affected by this relatively recent cosmic impact."

A comet collision with Earth caused abrupt environmental stress and degradation that contributed to the extinction of most large animal species then inhabiting the Americas, a group of scientists suggests. The catastrophic impact and the subsequent climate change also led to the disappearance of the prehistoric Clovis culture, and to human population decline. Now focus has turned to the character and distribution of nanodiamonds, one type of material produced during such an extraterrestrial collision. The researchers found an abundance of these tiny diamonds distributed over 50 million square kilometers across the Northern Hemisphere.

Early growth of giant galaxy, just 3 billion years after the Big Bang, revealed

Date:

August 27, 2014

Source:

Space Telescope Science Institute (STScI)

Summary:

The birth of massive galaxies, according to galaxy formation theories, begins with the buildup of a dense, compact core that is ablaze with the glow of millions of newly formed stars. Evidence of this early construction phase, however, has eluded astronomers — until now. Astronomers identified a dense galactic core, dubbed "Sparky," using a combination of data from several space telescopes. Hubble photographed the emerging galaxy as it looked 11 billion years ago, just 3 billion years after the birth of our universe in the big bang.

Astronomers have for the first time gotten a glimpse of the earliest stages of massive galaxy construction. The building site, dubbed "Sparky," is a developing galaxy containing a dense core that is blazing with the light of millions of newborn stars which are forming at a ferocious rate. The discovery was made possible through combining observations from NASA's Hubble and Spitzer space telescopes, the European Space Agency's Herschel Space Observatory, and the W.M. Keck Observatory in Hawaii.

Because the infant galaxy is so far away, it is seen as it appeared 11 billion years ago, just 3 billion years after the birth of the universe in the big bang. Astronomers think the compact galaxy will continue to grow, possibly becoming a giant elliptical galaxy, a gas-deficient assemblage of ancient stars theorized to develop from the inside out, with a compact core marking its beginnings.

"We really hadn't seen a formation process that could create things that are this dense," explained Erica Nelson of Yale University in New Haven, Connecticut, lead author of the science paper announcing the results. "We suspect that this core-formation process is a phenomenon unique to the early universe because the early universe, as a whole, was more compact. Today, the universe is so diffuse that it cannot create such objects anymore."

The research team's paper appears in the August 27 issue of the journal Nature.

Although only a fraction of the size of the Milky Way, the tiny powerhouse galaxy already contains about twice as many stars as our galaxy, all crammed into a region only 6,000 light-years across. The Milky Way is about 100,000 light-years across. The barely visible galaxy may be representative of a much larger population of similar objects that are obscured by dust.

"They're very extreme environments," Nelson said. "It's like a medieval cauldron forging stars. There's a lot of turbulence, and it's bubbling. If you were in there, the night sky would be bright with young stars, and there would be a lot of dust, gas, and remnants of exploding stars. To actually see this happening is fascinating."

Alongside determining the galaxy's size from the Hubble images, the team dug into archival far-infrared images from the Spitzer and Herschel telescopes. The analysis allowed them to see how fast the young galaxy is churning out stars. Sparky is producing roughly 300 stars per year. By comparison, the Milky Way produces roughly 10 stars per year.

Astronomers believe that this frenzied star formation occurred because the galactic center is forming deep inside a gravitational well of dark matter, an invisible form of matter that makes up the scaffolding upon which galaxies formed in the early universe. A torrent of gas is flowing into this well at the galaxy's core, sparking waves of star birth.

The sheer amount of gas and dust within an extreme star-forming region like this may explain why these compact galaxies have eluded astronomers until now. Bursts of star formation create dust, which builds up within the forming galaxy and can block some starlight. Sparky was only barely visible, and it required the infrared capabilities of Hubble's Wide Field Camera 3, Spitzer, and Herschel to reveal the developing galaxy.

The observations indicate that the galaxy had been furiously making stars for more than a billion years (at the time the light we now observe began its long journey). But the galaxy didn't keep up this frenetic pace for very long, the researchers suggested. Eventually, the galaxy probably stopped forming stars in the packed core. Smaller galaxies then might have merged with the growing galaxy, making it expand outward in size over the next 10 billion years, possibly becoming similar to one of the mammoth, sedate elliptical galaxies seen today.

"I think our discovery settles the question of whether this mode of building galaxies actually happened or not," said team member Pieter van Dokkum of Yale University. "The question now is, how often did this occur? We suspect there are other galaxies like this that are even fainter in near-infrared wavelengths. We think they'll be brighter at longer wavelengths, and so it will really be up to future infrared telescopes such as NASA's James Webb Space Telescope to find more of these objects."

Detecting neutrinos, physicists look into the heart of the sun

Date:

August 27, 2014

Source:

University of Massachusetts at Amherst

Summary:

Using one of the most sensitive neutrino detectors on the planet, physicists have directly detected neutrinos created by the 'keystone' proton-proton fusion process going on at the sun's core for the first time.

sing one of the most sensitive neutrino detectors on the planet, an international team of physicists including Andrea Pocar, Laura Cadonati and doctoral student Keith Otis at the University of Massachusetts Amherst report in the current issue of Nature that for the first time they have directly detected neutrinos created by the "keystone" proton-proton (pp) fusion process going on at the sun's core.

The pp reaction is the first step of a reaction sequence responsible for about 99 percent of the Sun's power, Pocar explains. Solar neutrinos are produced in nuclear processes and radioactive decays of different elements during fusion reactions at the Sun's core. These particles stream out of the star at nearly the speed of light, as many as 420 billion hitting every square inch of the Earth's surface per second.

Because they only interact through the nuclear weak force, they pass through matter virtually unaffected, which makes them very difficult to detect and distinguish from trace nuclear decays of ordinary materials, he adds.

The UMass Amherst physicist, one principal investigator on a team of more than 100 scientists, says, "With these latest neutrino data, we are directly looking at the originator of the sun's biggest energy producing process, or chain of reactions, going on in its extremely hot, dense core. While the light we see from the Sun in our daily life reaches us in about eight minutes, it takes tens of thousands of years for energy radiating from the sun's center to be emitted as light."

"By comparing the two different types of solar energy radiated, as neutrinos and as surface light, we obtain experimental information about the Sun's thermodynamic equilibrium over about a 100,000-year timescale," Pocar adds. "If the eyes are the mirror of the soul, with these neutrinos, we are looking not just at its face, but directly into its core. We have glimpsed the sun's soul."

"As far as we know, neutrinos are the only way we have of looking into the Sun's interior. These pp neutrinos, emitted when two protons fuse forming a deuteron, are particularly hard to study. This is because they are low energy, in the range where natural radioactivity is very abundant and masks the signal from their interaction."

The Borexino instrument, located deep beneath Italy's Apennine Mountains, detects neutrinos as they interact with the electrons of an ultra-pure organic liquid scintillator at the center of a large sphere surrounded by 1,000 tons of water. Its great depth and many onion-like protective layers maintain the core as the most radiation-free medium on the planet.

Indeed, it is the only detector on Earth capable of observing the entire spectrum of solar neutrino simultaneously. Neutrinos come in three types, or "flavors." Those from the Sun's core are of the "electron" flavor, and as they travel away from their birthplace, they oscillate or change between two other flavors, "muon" to "tau." With this and previous solar neutrino measurements, the Borexino experiment has strongly confirmed this behavior of the elusive particles, Pocar says.

One of the crucial challenges in using Borexino is the need to control and precisely quantify all background radiation. Pocar says the organic scintillator at Borexino's center is filled with a benzene-like liquid derived from "really, really old, millions-of-years-old petroleum," among the oldest they could find on Earth.

"We needed this because we want all the Carbon-14 to have decayed, or as much of it as possible, because carbon-14 beta decays cover the neutrino signals we want to detect. We know there is only three atoms of C14 for each billion, billion atoms in the scintillator, which shows how ridiculously clean it is."

A related problem the physicists discuss in their new paper is that when two C14 atoms in the scintillator decay simultaneously, an event they call a "pileup," its signature is similar to that of a pp solar neutrino interaction. In a great advance for the analysis, Pocar says, "Keith Otis figured out a way to solve the problem of statistically identifying and subtracting these pileup events from the data, which basically makes this new pp neutrino analysis process possible."

Though detecting pp neutrinos was not part of the original National Science Foundation-sponsored Borexino experiment, "it's a little bit of a coup that we could do it," the astrophysicist says. "We pushed the detector sensitivity to a limit that has never been achieved before."

Neuroscientists reverse memories' emotional associations: Brain circuit that links feelings to memories manipulated

Date:

August 27, 2014

Source:

Massachusetts Institute of Technology

Summary:

Most memories have some kind of emotion associated with them: Recalling the week you just spent at the beach probably makes you feel happy, while reflecting on being bullied provokes more negative feelings. A new study from neuroscientists reveals the brain circuit that controls how memories become linked with positive or negative emotions.

A new study from MIT neuroscientists reveals the brain circuit that controls how memories become linked with positive or negative emotions. Furthermore, the researchers found that they could reverse the emotional association of specific memories by manipulating brain cells with optogenetics -- a technique that uses light to control neuron activity.The findings, described in the Aug. 27 issue ofNature, demonstrated that a neuronal circuit connecting the hippocampus and the amygdala plays a critical role in associating emotion with memory. This circuit could offer a target for new drugs to help treat conditions such as post-traumatic stress disorder, the researchers say.

Most memories have some kind of emotion associated with them: Recalling the week you just spent at the beach probably makes you feel happy, while reflecting on being bullied provokes more negative feelings.

"In the future, one may be able to develop methods that help people to remember positive memories more strongly than negative ones," says Susumu Tonegawa, the Picower Professor of Biology and Neuroscience, director of the RIKEN-MIT Center for Neural Circuit Genetics at MIT's Picower Institute for Learning and Memory, and senior author of the paper.

The paper's lead authors are Roger Redondo, a Howard Hughes Medical Institute postdoc at MIT, and Joshua Kim, a graduate student in MIT's Department of Biology.

Shifting memories

Memories are made of many elements, which are stored in different parts of the brain. A memory's context, including information about the location where the event took place, is stored in cells of the hippocampus, while emotions linked to that memory are found in the amygdala.

Previous research has shown that many aspects of memory, including emotional associations, are malleable. Psychotherapists have taken advantage of this to help patients suffering from depression and post-traumatic stress disorder, but the neural circuitry underlying such malleability is not known.

In this study, the researchers set out to explore that malleability with an experimental technique they recently devised that allows them to tag neurons that encode a specific memory, or engram. To achieve this, they label hippocampal cells that are turned on during memory formation with a light-sensitive protein called channelrhodopsin. From that point on, any time those cells are activated with light, the mice recall the memory encoded by that group of cells.

Last year, Tonegawa's lab used this technique to implant, or "incept," false memories in mice by reactivating engrams while the mice were undergoing a different experience. In the new study, the researchers wanted to investigate how the context of a memory becomes linked to a particular emotion. First, they used their engram-labeling protocol to tag neurons associated with either a rewarding experience (for male mice, socializing with a female mouse) or an unpleasant experience (a mild electrical shock). In this first set of experiments, the researchers labeled memory cells in a part of the hippocampus called the dentate gyrus.

Two days later, the mice were placed into a large rectangular arena. For three minutes, the researchers recorded which half of the arena the mice naturally preferred. Then, for mice that had received the fear conditioning, the researchers stimulated the labeled cells in the dentate gyrus with light whenever the mice went into the preferred side. The mice soon began avoiding that area, showing that the reactivation of the fear memory had been successful.

The reward memory could also be reactivated: For mice that were reward-conditioned, the researchers stimulated them with light whenever they went into the less-preferred side, and they soon began to spend more time there, recalling the pleasant memory.

A couple of days later, the researchers tried to reverse the mice's emotional responses. For male mice that had originally received the fear conditioning, they activated the memory cells involved in the fear memory with light for 12 minutes while the mice spent time with female mice. For mice that had initially received the reward conditioning, memory cells were activated while they received mild electric shocks.

Next, the researchers again put the mice in the large two-zone arena. This time, the mice that had originally been conditioned with fear and had avoided the side of the chamber where their hippocampal cells were activated by the laser now began to spend more time in that side when their hippocampal cells were activated, showing that a pleasant association had replaced the fearful one. This reversal also took place in mice that went from reward to fear conditioning.

Altered connections

The researchers then performed the same set of experiments but labeled memory cells in the basolateral amygdala, a region involved in processing emotions. This time, they could not induce a switch by reactivating those cells -- the mice continued to behave as they had been conditioned when the memory cells were first labeled.

This suggests that emotional associations, also called valences, are encoded somewhere in the neural circuitry that connects the dentate gyrus to the amygdala, the researchers say. A fearful experience strengthens the connections between the hippocampal engram and fear-encoding cells in the amygdala, but that connection can be weakened later on as new connections are formed between the hippocampus and amygdala cells that encode positive associations.

"That plasticity of the connection between the hippocampus and the amygdala plays a crucial role in the switching of the valence of the memory," Tonegawa says.

These results indicate that while dentate gyrus cells are neutral with respect to emotion, individual amygdala cells are precommitted to encode fear or reward memory. The researchers are now trying to discover molecular signatures of these two types of amygdala cells. They are also investigating whether reactivating pleasant memories has any effect on depression, in hopes of identifying new targets for drugs to treat depression and post-traumatic stress disorder.

David Anderson, a professor of biology at the California Institute of Technology, says the study makes an important contribution to neuroscientists' fundamental understanding of the brain and also has potential implications for treating mental illness.

"This is a tour de force of modern molecular-biology-based methods for analyzing processes, such as learning and memory, at the neural-circuitry level. It's one of the most sophisticated studies of this type that I've seen," he says.