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Theory Of Sun's Role In Formation Of Solar System Questioned

Theory Of Sun's Role In Formation Of Solar System Questioned


A strange mix of oxygen found in a stony meteorite that exploded over Pueblito de Allende, Mexico nearly 40 years ago has puzzled scientists ever since.

Small flecks of minerals lodged in the stone and thought to date from the beginning of the solar system have a pattern of oxygen types, or isotopes, that differs from those found in all known planetary rocks, including those from Earth, its Moon and meteorites from Mars.

Now scientists from UC San Diego and Lawrence Berkeley National Laboratory have eliminated one model proposed to explain the anomaly: the idea that light from the early Sun could have shifted the balance of oxygen isotopes in molecules that formed after it turned on. When they beamed light through carbon monoxide gas to form carbon dioxide, the balance of oxygen isotopes in the new molecules failed to shift in ways predicted by the model they report in the September 5 issue of Science.

"It's solar system forensics. We're understanding a little about how it got made," said Mark Thiemens, Dean of the Division of Physical Sciences and a professor of chemistry and biochemistry at UC San Diego, who directed the project. The results pare down the potential explanations for how gas and dust coalesced to form the planets and will help this team and others interpret samples of the solar wind returned by NASA's Genesis spacecraft.

Atomic Shield

Scientists think the early Sun emitted intense far-ultraviolet light. Light energy at these very short wavelengths will dislodge oxygen atoms from molecules, freeing them to hook up with others in new combinations. In the process, the oxygen atoms absorb some of the energy.

This is how gases became dust and then larger minerals that collided and continued to build to form the planets. Oxygen, the most abundant element in the solar system, is a player in almost all of these reactions.

Each oxygen isotope responds to a unique set of light wavelengths. An abundance of a particular oxygen isotope within in a cloud of gas molecules will quench the light at its preferred wavelengths, shielding gas molecules farther along the light's path. Other wavelengths, including those that dislodge different oxygen isotopes, will continue unimpeded, favoring the inclusion of these rarer isotopes in new molecules.

The balance of oxygen isotopes found in the Allende meteorite is tipped toward the most abundant one, 16O. Planetary rocks have relatively more rarer heavier oxygen isotopes, as though rare isotopes were preferred as the planets formed.

Photo Effect

"We decided to directly test this idea that photoshielding could change the isotope ratios," said Subrata Chakraborty, a postdoctoral fellow at UC San Diego and first author of the paper.

The team focused an intense beam of far-ultraviolet light generated by the Lawrence Berkeley National Laboratory's Advanced Light Source into a tube filled with carbon monoxide gas. The light knocked some of the oxygen atoms free, allowing them to recombine with other carbon monoxide molecules to form carbon dioxide. Chakraborty then collected and analyzed the carbon dioxide to determine the balance of oxygen isotopes in the new molecules.

By precisely controlling the wavelength of the light, the scientists were able to set up conditions that should have resulted in oxygen isotope mixes that matched either those found on Earth or in the Allende meteorite.

Wavelengths known to be absorbed by 16O should result in carbon dioxide molecules enriched with the heavier forms of oxygen. They tested two of these wavelengths: one enriched the mix; the other did not.

Wavelengths not absorbed by 16O should result in a mix that matched that found in the Allende meteorite. Again, of the two the team tested, one did and one did not. "Some process is altering the mix, but it can't be photoshielding," Chakraborty said.

Original Mix

Samples returned by the GENESIS spacecraft will have to be interpreted in light of these results, Thiemens said. By analyzing samples of the Sun's outer atmosphere captured from the solar wind, the mission aims to determine the original composition of the solar nebula, the swirl of dust and gas that formed the solar system. Measurements by Thiemen's research group and others will help to resolve the chemical mismatch between the meteorite inclusions and planetary rocks.

Several other models have been proposed to explain the anomaly--including the idea that an exploding star could have blasted in an extra dose of 16O--only to have been discarded when experimental evidence showed them to be unlikely.

The only one left standing, according to Thiemens, is an idea called molecular symmetry that says an atom flanked by two oxygen isotopes is more likely to become a stable molecule if the two isotopes are mismatched. This quieter process would also favor the formation of molecules that included rarer oxygen isotopes.

"There's no violence," Thiemens said. "It doesn't require a star blowing up or turning on to cast a nebula-wide shadow. It's symmetry."

Musahid Ahmed of Lawrence Berkeley National Laboratory and Teresa Jackson of UC San Diego are co-authors of the paper. NASA and the Department of Energy funded the project.

Forensic Scientists Improve DNA Analysis With Mummy-inspired Bone-baking

Baking Out DNA

Forensic Scientists Improve DNA Analysis With Mummy-inspired Bone-baking

Forensic scientists analyzing bones found in the Gobi desert discovered that the DNA within them could be surprisingly easily extracted. In an experiment designed to mimic the conditions that affected those bones, baking a particularly difficult sample made the DNA much more easily extracted, probably because it makes it easier to break open more cells and expose more of the DNA molecules.

Mummies have always held secrets, but now one of them has led to a new DNA technique.

Our fascination with mummies has sold millions at the box office. Now these preserved people -- mummies more than 800 years old -- are helping scientists reveal the mysteries of the past.

University of New Haven forensic scientist Dr. Heather Coyle is experimenting with a new technique by going back in time.

These are skeletal remains recently gathered from a Gobi desert cave. Surprisingly, Dr. Coyle was able to extract DNA from these mummies, but when she tried the same method on a body found in the USA, she was not as successful. "We realized that the bone we were trying to process was not yielding DNA from the case we were working on," Dr. Coyle said.

Standard DNA procedure for bones is to freeze them. When Coyle and her team re-examined the mummy remains they realized the Gobi desert created a natural bone baking process.

"It makes the bone more brittle so it makes it easier to grind and break open more cells, so we think we are accessing more DNA to begin with," Dr. Coyle said. Dr. Coyle decided to mimic nature by baking the cold case bones for 72 hours. Liquid nitrogen was then poured into a pulverizer. The bone was placed inside, ready to be crushed. After a short cycle the bone was turned to powder and ready for DNA extraction.

Coyle hopes her new technique will someday help close the book on several cold case files.

What is DNA? DNA is the blueprint that encodes all the data for building a human body, along with instructions on how it should operate. Every cell in a person's body contains a copy of this DNA.

DNA typing is based on an unusual feature found in the human genome. There are multiple copies of certain short sequences, 3 to 30 base pairs long, that are repeated one after another as many as 100 times. These groups of repeat sequences are widely scattered through the genome. Everyone has these repeat units, but the number varies from person to person.

Only identical twins will have the same numbers and patterns of these sequences. These genetic data aren't instructions to make anything; scientists think they might exist to get mixed up in the regular genes and provide some variety for evolution.

Person's Geographic Origins Located From DNA

Person's Geographic Origins Located From DNA


One day soon, you may be able to pinpoint the geographic origins of your ancestors based on analysis of your DNA.

A study published online this week in Nature by an international team that included Cornell University researchers describes the use of DNA to predict the geographic origins of individuals from a sample of Europeans, often within a few hundred kilometers of where they were born.

"What we found is that within Europe, individuals with all four grandparents from a given region are slightly more similar genetically to one another, on average, than to individuals from more distant regions," said Carlos Bustamante, associate professor of biological statistics and computational biology at Cornell and the paper's senior author. John Novembre, an assistant professor in the University of California-Los Angeles' Department of Ecology and Evolution, was lead author of the study that also included researchers from GlaxoSmithKline, the University of Chicago and the University of Lausanne (Switzerland).

"When these minute differences are compounded across the whole of their genome, we have surprisingly high power to predict where in Europe they came from," Bustamante added.

This is one of the first studies to examine genome-wide patterns of genetic variation across a large sample of Europeans, and to use these data to predict ancestry. The methodology has wide-ranging implications for using DNA samples from unrelated individuals to identify genes underlying complex diseases, as well as forensics, personalized genomics and the study of recent human history.

Using data from a sample of almost 3,200 Europeans supplied by GlaxoSmithKline, the team analyzed more than 500,000 genetic points known as single nucleotide polymorphisms (SNPs), or minute sequence variations in DNA. The researchers focused its analysis on individuals for whom all the grandparents were believed to come from the same country. The team simplified and plotted the data, revealing that individuals with similar genetic structures clustered together on the plot in such a way that the major geographic features of Europe became distinguishable.

"What is really surprising is that when we summarize the data from 500,000 SNPs in just two dimensions, we see this striking map of Europe," said Novembre. "We can recognize the Iberian peninsula, the Italian peninsula, southeastern Europe, Turkey and Cyprus."

The resolution of the genetic map was so precise that the investigators were able to find genetic differences among the French, German and Italian-speaking Swiss individuals; with French speakers being more similar to the French, German speakers to Germans and Italian speakers to Italians.

Based on these observations, Novembre and colleagues from the University of Chicago developed a novel algorithm for classifying individuals geographically based on their patterns of DNA variation.

For well-sampled countries, this approach placed 50 percent of individuals within 310 kilometers (km) of their reported origin, and 90 percent within 700 km of their origin. Across all populations, 50 percent of individuals were placed within 540 km of their reported origin and 90 percent of individuals within 840 km. The findings excluded individuals with grandparents from different countries, since these were assigned locations between their grandparents' origins. Some next steps will be to infer origins for people with recent ancestry from multiple locations and to perform similar analyses for populations on other continents.

The study was funded by the Giorgi-Cavaglieri Foundation, the Swiss National Science Foundation, the National Science Foundation and the National Institutes of Health in the U.S., and GlaxoSmithKline.