250 million years ago something wiped out most life
Posted: Friday, January 18, 2002
Source: Space Telescope Science Institute (http://www.stsci.edu/)
The deepest views of the cosmos from NASA's Hubble Space Telescope are yielding clues that the very first stars may have burst into the universe as brilliantly and spectacularly as a fireworks finale - except, in this case, the finale came first - long before Earth, our Sun and the Milky Way Galaxy formed.
If this interpretation is correct, it offers a tantalizing possibility that astronomers may behold this stellar blaze of glory when they use NASA's Next Generation Space Telescope and other future space telescopes to probe even farther into the very early universe.
Studies of Hubble's deepest views of the heavens by Kenneth M. Lanzetta of the State University of New York (SUNY) at Stony Brook, and colleagues, lead to the preliminary conclusion that the universe made a significant portion of its stars in a torrential firestorm of star birth which abruptly lit up the pitch-dark heavens just a few hundred million years after the big bang. Though stars continue to be born today in galaxies, the star birth rate could be a trickle compared to the predicted gusher of stars in those opulent early years.
This new idea of a continually escalating rate of star birth the farther Hubble looks back in time offers a dramatic revision of previous Hubble Deep Field studies that proposed that the star birth rate in the early universe ramped up to a "baby boom" about halfway back to the beginning of the universe.
Lanzetta bases his conclusion on a new analysis of galaxies in the Hubble deep fields taken near the north and south celestial poles (in 1995 and 1998 respectively). He reports in an upcoming issue of the Astrophysical Journal that the farthest objects in the deep fields are only the "tip of the iceberg" of an effervescent period of star birth that is unlike anything the universe will ever see again. Lanzetta concludes that 90 percent of the light from the early universe is missing in the Hubble deep fields. "The previous census of the deep fields missed most of the ultraviolet light in the universe; most of it is invisible," he says.
Based on an analysis of galaxy colors, Lanzetta concludes that the farthest objects in the deep fields must be extremely intense, unexpectedly bright knots of blue-white, hot newborn stars embedded in primordial galaxies that are too faint to be seen even by Hubble's far vision. It's like seeing only the lights on a distant Christmas tree and inferring the presence of the whole tree.
The missing light is deduced much as one might deduce the attendance at a neighbor's party by peering over a tall fence. If all one could see were people over six feet tall, one would conclude that there were many more people at the party that couldn't be seen. This conclusion would be based on an assumption about the average heights of people.
Likewise, Lanzetta's analysis is based on carefully extrapolating back into time from the conditions in the present universe. Because such far extrapolations are built on certain assumptions, this conclusion will require further analysis and observation.
Lanzetta next plans to use Hubble's Advanced Camera for Surveys (to be installed in early 2002) to look even deeper into the universe to try to directly verify some portion of the missing light. He will also look for very distant supernovae as an alternate measure of star formation. "Because they are point sources of light, supernovae are not subject to the same cosmological brightness dimming effects like galaxies (which are extended sources of light)," says Lanzetta.
The universe could go on making stars for trillions of years to come, before all the hydrogen is used up, or is too diffuse to coalesce. But the universe will never again resemble the star-studded tapestry that brought light back to the darkness.
Editor's Note: The original news release can be found at http://oposite.stsci.edu/pubinfo/pr/2002/02/pr.html
Send page by E-Mail Geneticist Addresses Evolutionary Puzzle
Posted: Thursday, January 10, 2002
October 5, 1998, The University of Texas
A study involving the genetic profiles of more than two dozen Chinese populations supports a theory that modern Chinese people have descended from a common African ancestor. These findings mirror the commonly held belief that all the world’s races descended from the same ancestor.
Li Jin, Ph.D., an assistant professor at UT-Houston Human Genetics Center, School of Public Health http://www.uth.tmc.edu/uth_orgs/pub_affairs/facts/sph.html, spearheaded a collaborative five-year effort, the Chinese Human Genome Diversity Project. The work was funded by the National Natural Sciences Foundation of China. Twelve other researchers from seven institutions collaborated on the project. Jin’s article appears in the Sept. 29 issue of the Proceedings of the National Academy of Sciences, a biweekly journal.
Jin used recently discovered genetic markers known as "microsatellites." Microsatellites are repeats of short stretches of DNA that have high mutation rates. They contain more information per gene than traditional markers, and can help make distinctions between closely related population groups.
"The results of this study have strong implications for biomedical researchers," Jin said. "We have to know the genetic differences between populations, so we can find the correct target population in order to study complex diseases like diabetes."
Microsatellites were used to examine the genetic profiles of 28 of the 56 official Chinese ethnic groups, along with 15 worldwide populations. Study results indicate that the majority of the Chinese gene pool has African origins.
Anthropologists are divided over the origin of modern Chinese humans. Some claim human fossil remains unearthed in China point to the independent origin of Chinese Man, while others question the validity of those findings.
Jin stresses that genetic differences among individual human beings account for up to 85 percent of the entire genetic spectrum, while the genetic differences in the world population are only about 15 percent. "No matter which ethnic group you come from, we’re all pretty much the same."
The study also confirms a genetic distinction between northern and southern Chinese populations, and gives rise to the theory that Northern Chinese ethnic groups may actually be a subset of Southern Chinese. It was widely believed that since the origin of Chinese culture occurred in mid- to northern Asia, then modern Chinese Man must have originated there, also.
"Prehistoric migration patterns indicate Southern Chinese moving north probably about 50,000 years ago, and then becoming geographically isolated from their ancestors. So, the cultural and genetic histories of modern Chinese humans are apparently not one and the same," Jin said.
The study has not only stimulated new discussion of prehistoric migration patterns in East Asia, it has also proved the effectiveness of microsatellites in revealing major patterns of evolutionary history among closely related populations.
©1998 The University of Texas Houston Health Science Center. Permission to reprint is available upon request. Contact Scott Merville, 1200 University Center Tower, 7000 Fannin, Houston, Texas 77030, 713/500-3042 (phone), 713/500 3052 (fax), email@example.com mailto:firstname.lastname@example.org.
Send page by E-Mail Study traces genetic origin of Chinese to Africa
Posted: Thursday, January 10, 2002
by Robert Lee Hotz, Los Angeles Times, Sept 29, 1998
Most of the population of modern China owes its genetic origins to Africa, an international scientific team reports in research that undercuts any claim that modern humans may have originated independently in China.
In the search for human origins, in which political beliefs and pride of place can figure as much as fossil evidence, the new genetic findings dramatically illustrate the intricate weave of prehistoric migrations and human evolution, the scientists said.
The researchers also demonstrated that the peoples of northern and southern China cluster into distinct regional genetic populations that share inherited characteristics. Those groups, in turn, can be divided into even smaller, separate genetic groups. Yet, overall, they all are descendants of a single population group that may have migrated into China eons before humans learned to write or forge metal tools, the new research suggests.
Published in today's edition of the Proceedings of the National Academy of Sciences, the study is the product of the Chinese Human Genome Diversity Project, a consortium of seven major research groups in the People's Republic of China, and the Human Genetics Center at the University of Texas at Houston. It was funded by the National Natural Science Foundation of China.
The group used the advanced tools of DNA analysis to create detailed genetic profiles of 28 of China's official population groups, which make up more than 90 percent of the country's population, to try to understand the roots of complex chronic diseases such as diabetes and hypertension.
By exploring the genetic relationships among China's ethnic groups, the team also shed light on the ancestry of people in East Asia, who, like everyone, carry in every cell of their bodies genetic hints to their evolutionary history and the journeys of their forebears.
In all, the Chinese government today recognizes 56 ethnic groups. Just one of them, the Han, makes up the bulk of the population, comprising about 1.1 billion people. The 55 other ethnic minority groups encompass about 100 million people.
To study the diverse genetic inheritance of such an enormous population, the researchers used a special set of genetic markers called microsatellites. These extremely short chemical segments of DNA mutate very rapidly. That lets scientists use them as signposts to mark how populations diverged or merged over time, reconstructing their evolutionary journey across time and the continents to their present homes.
The scientists looked at 30 such microsatellite markers across 28 of the population groups in China and compared the pattern to 11 other population groups around the world.
"Populations from East Asia always derived from a single lineage, indicating the single origins of those populations," they said. "It is now probably safe to conclude that modern humans originating in Africa constitute the majority of the current gene pool in East Asia," they said.
While few scholars today dispute the idea that the earliest ancestors of the human species evolved in Africa, there still is considerable debate over how modern humanity evolved from its more primitive ancestors.
Many anthropologists believe humans may have migrated out of Africa in waves. More than a million years ago, humanity's primitive ancestors, known as Homo erectus, walked out of Africa to colonize Europe, the Middle East and Asia. On that everyone agrees.
Then several hundred thousand years later, some theorize, a second wave of more sophisticated tool-using humans migrated out of Africa and overwhelmed those earlier ancestors. By that theory, modern humans are descended only from those sophisticated tool-users.
Other researchers dispute that pattern. In their view, there was no second wave of migration from Africa. Instead, they believe, humankind evolved in China and elsewhere as colonies of more primitive Homo erectus intermarried in a global network of genetic relationships.
"The issue," said University of Michigan anthropologist Milford Wilpoff, "is about whether people have multiple ancestors from many places or one ancestor from one place."
Copyright © 2002 The Seattle Times Company
Send page by E-Mail Primordial Air May Have Been "Breathable"
Posted: Thursday, January 10, 2002
Source: CSIRO Australia (http://www.csiro.au/)
The Earth may have had an oxygen-rich atmosphere as long ago as three billion years and possibly even earlier, three leading geologists have claimed. Their theory challenges long-held ideas about when the Earth's atmosphere became enriched with oxygen, and pushes the likely date for formation of an atmosphere resembling today's far back into the early history of the planet.
It may also revolutionise the worldwide search for gold and other minerals, and raises new questions about when and how life could have arisen.
Evidence for the presence of oxygen in the primitive atmosphere was put forward by the Chief of CSIRO Exploration and Mining Professor Neil Phillips, Australian-based South African geologist Mr Jonathan Law and US gold mining consultant Dr Russell Myers in a publication by the Society for Economic Geology.
"These findings may have enormous economic implications in that we may simply have been looking in the wrong places for massive gold deposits like South Africa's Witwatersrand," says Professor Phillips.
"Or we may actually have found them – and not recognised them for what they are, because we did not understand the processes involved in their formation."
The scientists base their case on the presence of iron-rich nodules in the deep strata of the Witwatersrand – nodules they believe are pisoliths, small balls containing ferric iron produced by exposure to an oxygen-rich air.
Pisoliths still form nowadays and provide important clues in the search for minerals, including gold. Those found in the Rand come from levels 3-4 kilometres down, which are securely dated at 2.7 to 2.8 billion years old.
The researchers' theory has been lent additional weight by evidence from the Western Australian Pilbara region for the presence of sulphates in rocks up to 3.5 billion years old. These, too, could not have formed without an oxygen-rich atmosphere.
Pisoliths have been a vital tool in the discovery of $5 billion worth of new gold deposits in WA in recent years, using techniques developed by CSIRO's Dr Ray Smith, Dr Charles Butt and Dr Ravi Anand. The small iron-rich balls form from iron in groundwater and ‘scavenge' traces of other minerals in the local environment. They provide clues, like fingerprints, which point to deposits lying hidden beneath metres of inscrutable surface rubble.
By analysing pisoliths over a wide area for gold content, geologists can construct a pattern of steadily enriching traces, with the hidden deposit lying like a bullseye at the heart of it, usually a bit uphill.
Some geologists believe living organisms may play a part in the formation of pisoliths, raising tantalising questions about the nature and role of life in shaping the Earth's early surface and mineralisation.
The presence of pisoliths in the deep strata of the Rand suggests that the conditions for mineral formation 3 billion years or so ago were different to what many geologists have believed for the past half-century, the team say. These ideas have already been integrated into a new exploration model for the formation of the Rand deposits by the same researchers.
The Rand is unique on Earth – a vast body of rock very rich in gold. The mightiest gold deposit ever found. Nothing like it has been discovered elsewhere.
Professor Phillips says that this may be because we didn't know what to look for, because we made wrong assumptions about the conditions in which it formed.
In other words, fresh Rands may still await discovery. Some geologists speculate one of them, at least, lies in central Western Australia.
Editor's Note: The original news release can be found at http://www.csiro.au/index.asp?type=mediaRelease&id=Prpisoliths
Send page by E-Mail Discovery Overturns Long-Held Genetic Belief
Posted: Monday, January 7, 2002
Source: University Of Chicago Medical Center (http://www.medcenter.uchicago.edu/)
A classic belief found in genetics and evolution textbooks since the 1930s has been overturned by powerful new techniques combined with the willingness to question dogma.
Researchers from the University of Chicago report in the January 4, 2002, issue of Science that, contrary to expectations, the tiny fourth chromosome of the fruit fly, believed to be identical in every member of the species, actually has several regions that vary.
"This classic conviction of genetics and evolution, this rock-bottom-solid conclusion, which has become a textbook example of natural selection's propensity to eliminate variation from closely linked genes, just doesn't hold up," said Manyuan Long, Ph.D. assistant professor of ecology and evolution at the University of Chicago and director of the study.
Since 1906, Drosophila melanogaster, the common fruit fly, has been at the center of genetic research. The proof that genes exist on chromosomes like beads on a string, that they are linked together, that they can be mapped, even the method of naming genes, comes from early research on fruit flies.
The synthesis of Darwin's theories about evolution and Mendel's discoveries about genetics was made using fruit flies. And the discovery of recombination, in which paired chromosomes can exchange genes as they form egg or sperm cells and thus increase genetic diversity, derived from early work on the four chromosomes of the fruit fly.
Despite the fly's century in the laboratory limelight, it's tiny fourth chromosome -- which contains only one percent of the insect's coding DNA -- has been comparatively neglected. Based on limited evidence available at the time, the pioneers, including Calvin Bridges and Nobel Prize winner Hermann Muller, determined that there were no genetic crossovers -- meaning no exchange of hereditary information -- on this tiny chromosome.
This belief helped to inspire elaborate theories about the consequences of a nonrecombinant chromosome, introducing the concepts of "selective sweeps" and "genetic hitchhiking." If a mutated gene on Chromosome 4 conferred a sufficient survival advantage, the experts posited, the entire advantageous chromosome, rather than the single gene, would sweep through a population, carrying along the founder's version of every gene on that chromosome, thus eliminating all variation.
In 1991, as a graduate student in Martin Kreitman's laboratory at the University of Chicago, one of the authors of the current Science paper tested the theory. Andrew Berry (now a researcher at Harvard's Museum of Comparative Zoology) sequenced the cubitus interruptus gene, on Chromosome 4, from 10 natural lines of Drosophila melanogaster. All ten were identical.
Long's research team, including postdoctoral fellow Wen Wang, Ph.D., and genetics graduate student Kevin Thornton, became suspicious, however, when Wang identified sphinx, a new gene with several variations. Sphinx was on Chromosome 4. So they analyzed the sphinx gene from Drosophila melanogaster populations from all over the world.
They found high levels of variation within this gene and in other scattered sites on Chromosome 4. The level of variation was similar to genes in regions on other chromosomes with normal levels of recombination. They also found recombination at at least six sites on the chromosome.
After looking at multiple sites from many populations, Long and colleagues determined that Chromosome 4 could be divided into three discrete domains: a proximal region (near the centromere, and including the cubitus interruptus gene) with no variation, the central region around sphinx (nearly 20 percent of the chromosome) with normal levels of variation, and a region farther out with low variation.
"This indicates that the fourth chromosome is not evolving as a single unit," note the authors; "different regions appear to have different evolutionary histories."
Another surprise was an unusual distribution pattern for the highly variable region. The researchers found two very different versions of this region. The ratio between the two versions was consistent for fly populations from all over the world: evidence that fruit flies "must embrace diversity, even on Chromosome 4, to survive," said Long.
"This should lay to rest the 70-year-old notion that the fourth chromosome is non-recombining," added Long. "We have long thought of Chromosome 4 as the 'black hole' of genetics because we thought no variation could escape the relentless purging effect of natural selection on a non-recombining chromosome, but when we peered long enough and hard enough into this void it began to emit light."
The research was supported by grants from the National Science Foundation and by a Packard Fellowship awarded to Long.
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