Tuesday, July 27, 2010
7/27/2010 04:22:00 AM Publicado por Alquimia
Ancient Polynesians went from building small-scale temples to constructing monumental, pyramid-shaped temples in just 140 years, not in four or five centuries as previously calculated, according to research led by a University of California, Berkeley, anthropologist and published this week in the print edition of the journal Proceedings of the National Academy of Sciences (PNAS).
Patrick V. Kirch, a UC Berkeley professor of anthropology and of integrative biology and a Pacific Islands expert, said his research team applied a high-precision thorium/uranium dating process to samples of decorative veneers, large blocks and religious offerings — all of them made of coral — that were found in 22 temple sites on the Pacific island of Mo'orea. The process, commonly used on fossils, can precisely determine the age of calcium carbonate materials such as coral.
"Coral is almost ideal for this (process)," he said, "because it takes up uranium from sea water and stores it. Shells and other (oceanic) materials filter uranium out through their metabolic processes." Because the coral used in temple construction was collected while it was alive and was used quickly, the date of the final growth of the coral specimens gave researchers the dates of temple construction.
They linked a clear progression of architectural change and increasingly elaborate temples on Mo'orea from 1620 to 1760 A.D. to political competition, increasing stratification and hierarchy that accompanied the region's growing cult worship of 'Oro, a god of war and of fertility, and new sacred regalia and religious rituals that included human sacrifice.
"The construction of these massive temples with their ahu (altar platforms) reaching ever higher toward the heavens, was clearly an important part of the strategy of chiefly elite to gain favor with the gods and to assert their power and prestige over their people," the researchers wrote in their journal article.
"The neat thing about this is that this is the first time we've been able to show how fast ritualized architecture can develop elaborate, massive temples," Kirch said in a recent interview. The researchers note in their PNAS paper that the development of ritual architecture in the Oaxaca Valley in southern Mexico has been estimated to have taken more than 1,300 years.
Kirch said the people of Mo'orea did not reflect "cultures that were stagnant or slow — they used very sophisticated methods to vie for control, power and resources. We see sort of a race for power expressed through ritualization of gods. It's not dissimilar to what's happening in the world today."
The thorium/uranium process used on the coral found in Mo'orea temples also may yield new insights into the timetables for socio-political development elsewhere, such as along the coasts of the Indian Ocean and the Red Sea, where large populations of people have used coral from reefs in construction, Kirch said.
His team's work on Mo'orea extended a thorium/uranium analysis begun in 2004 of coral offerings found in ancient Hawaiian sites that helped date the development of divine kingship in Hawaii. The process has a huge advantage over standard methods such as radiocarbon dating, which is plagued by large error ranges, Kirch said. He added that radiocarbon dating nevertheless remains the only option for many archaeological projects.
Kirch noted that the thorium/uranium dating also is preferable to using oral histories passed along from generation to generation to assign chronological dates to political, cultural and material changes.
The oldest temples that his team examined were relatively small and used only natural corals as facings in their low, altar-like platforms. Around the mid-17th century, temples were built that used cut and dressed blocks of coral that rose up to a meter high to face the altars. The final architectural stage that appeared in the early 18th century featured the appearance of stepped altars and the first use of uniform-sized, pecked basalt cobbles in temple walls — changes linked to the rise of the 'Oro cult.
Using standard archaeological seriation techniques to evaluate the temple remains' architectural and morphological features, the researchers reported a good fit with the timeline provided by the thorium/uranium testing.
(Photo: Patrick V. Kirch)
University of California, Berkeley
7/27/2010 04:21:00 AM Publicado por Alquimia
The origin of the evolutionary game – the ability of animals (including humans) and plants to reproduce sexually, genetically recombine to repair DNA, and then produce eggs, sperm or pollen – is an unresolved mystery in biology.
In an article published in the July/August issue of BioScience, University of Arizona researchers Harris Bernstein and Carol Bernstein provide insights into the early evolution of sexual organisms and the role environmental stressors had on sexual reproduction as a key survival strategy.
The UA department of cell biology and anatomy researchers argue that eukaryotes, or cells with a nucleus, adapted their meiotic ability to recombine chromosomes sexually into new genetically distinct entities from their ancestors, called prokaryotic cells.
The ability to recombine chromosomes through meiosis gives rise to eggs and sperm in humans. According to the Bernsteins' theory, meiosis evolved to promote DNA repair, thereby greatly reducing DNA damage in resulting eggs and sperm.
After the repair during meiosis, when an egg meets a sperm, the chance of having a viable fetus is much improved, and the chance that the baby will have a newly arisen genetic defect is reduced.
Prokaryotic cells evolved to develop the ability to repair DNA through a process called transformation, which also promotes chromosome repair through a process called recombination.
In prokaryotic cells (which include bacteria), asexual reproduction is completed through a process called binary fission. In binary fission, each strand of the original double-stranded DNA molecule serves as template for the reproduction of a complementary strand as the cell readies to split into two parts.
Under certain conditions, these cells are capable of the exchange and repair of DNA through a process called transformation. Transformation is the transfer of a fragment of DNA from a donor cell to a recipient cell, followed by recombination in the recipient chromosome. The researchers call this bacterial process an early version of sex.
For eukaryotes, which include higher animals and plants as well as single-celled species such as yeast, reproduction occurs in two ways, through mitosis or meiosis.
In mitosis, one cell divides to produce two genetically identical cells. In cells committed to mitosis, if there is DNA damage, a good deal of the damage can be repaired, especially the damage on one strand of the DNA, where information on the opposite strand can direct the repair on the damaged strand of the double helical DNA.
Meiosis is required in sexual reproduction in eukaryotes. During meiosis, a cell with two copies of each chromosome, one from each parent, undergoes the process of recombination. This allows a special type of repair, not available during ordinary mitosis.
During meiotic recombination, the pairs of chromosomes line up next to each other, and if there is damage on either chromosome, repair can take place by recombination with the other chromosome. Meiotic recombination allows for the repair of damaged DNA as the chromosomes from each parent are broken and joined, resulting in different combinations of genes in each chromosome.
The prevailing theory is that eukaryotes developed the ability for meiosis and sexual reproduction from their ability to reproduce through mitosis and not from their early ancestor's ability to reproduce through transformation.
"Our proposal, that the sexual process of meiosis in eukaryotes arose from the sexual process of transformation in their bacterial ancestors, is a new and fundamentally different perspective that will likely generate controversy," the researchers predict.
Harris Bernstein is a professor of cell biology and anatomy. Carol Bernstein is an associate research professor of cell biology and anatomy.
"If it is assumed that meiosis arose only after mitosis was established, there would have been an extended period (while mitosis was evolving) when there was no meiosis, and therefore no sex, in eukaryotes. This assumption appears to be contradicted by evidence that the basic machinery for meiosis was present very early in eukaryote evolution," the authors state.
A key argument in their hypothesis is that in both prokaryotes and simple eukaryotes, sexual cycles are induced by stressful conditions. Thus, the recombinational repair promoted by transformation and meiosis is part of a survival strategy in response to stress.
"Coping with DNA damage appears to be a fundamental problem for all life. For instance, the average human cell incurs about 10,000 DNA damages per day, of which 50 are double-strand breaks. The DNA damages are mostly due to the reactive oxygen species generated when converting food into energy. Thus, efficient DNA recombinational repair is an adaptation for cell survival and for producing new offspring, in higher organisms, through meiosis," the researchers contend.
In bacteria – the most common prokaryote – transformation is typically induced by high cell density, nutritional limitation, or DNA-damaging conditions. In yeast, a eukaryote or protist, the meiotic sexual cycle is induced when the supply of nutrients becomes limiting or when the cells are exposed to oxidative stress and DNA damage, the team added.
"Observations suggest that facultative sex in bacteria and protists is often an adaptive response to stressful environmental conditions, as would be expected if transformation and meiosis were related adaptations," the researchers write.
(Photo: U. Arizona)
University of Arizona
7/27/2010 04:20:00 AM Publicado por Alquimia
A team of astronomers from Germany, Bulgaria and Poland have used a completely new technique to find an exotic extrasolar planet. The same approach is sensitive enough to find planets as small as the Earth in orbit around other stars.
The group, led by Dr Gracjan Maciejewski of Jena University in Germany, used Transit Timing Variation to detect a planet with 15 times the mass of the Earth in the system WASP-3, 700 light years from the Sun in the constellation of Lyra. They publish their work in the journal Monthly Notices of the Royal Astronomical Society.
Transit Timing Variation (TTV) was suggested as a new technique for discovering planets a few years ago. Transits take place where a planet moves in front of the star it orbits, temporarily blocking some of the light from the star. So far this method has been used to detect a number of planets and is being deployed by the Kepler and Corot space missions in its search for planets similar to the Earth.
If a (typically large) planet is found, then the gravity of additional smaller planets will tug on the larger object, causing deviations in the regular cycle of transits. The TTV technique compares the deviations with predictions made by extensive computer-based calculations, allowing astronomers to deduce the makeup of the planetary system.
For this search, the team used the 90-cm telescopes of the University Observatory Jena and the 60-cm telescope of the Rohzen National Astronomical Observatory in Bulgaria to study transits of WASP-3b, a large planet with 630 times the mass of the Earth.
“We detected periodic variations in the transit timing of WASP-3b. These variations can be explained by an additional planet in the system, with a mass of 15 Earth-mass (i.e. one Uranus mass) and a period of 3.75 days”, said Dr Maciejewski.
“In line with international rules, we called this new planet WASP-3c”. This newly discovered planet is among the least massive planets known to date and also the least massive planet known orbiting a star which is more massive than our Sun.
This is the first time that a new extra-solar planet has been discovered using this method. The new TTV approach is an indirect detection technique, like the previously successful transit method.
The discovery of the second, 15 Earth-mass planet makes the WASP-3 system very intriguing. The new planet appears to be trapped in an external orbit, twice as long as the orbit of the more massive planet. Such a configuration is probably a result of the early evolution of the system.
The TTV method is very attractive, because it is particularly sensitive to small perturbing planets, even down to the mass of the Earth. For example, an Earth-mass planet will pull on a typical gas giant planet orbiting close to its star and cause deviations in the timing of the larger objects’ transits of up to 1 minute.
This is a big enough effect to be detected with relatively small 1-m diameter telescopes and discoveries can be followed up with larger instruments. The team are now using the 10-m Hobby-Eberly Telescope in Texas to study WASP-3c in more detail.