Researchers find that the most common dating method can produce “spuriously old” dates.A team from Europe took a closer look at how uranium-lead ages are determined, and found problems. One of the assumptions going into dating zircons (zirconium silicate crystals encasing uranium that decays to lead) is that the clock is “reset” when the parent rock under goes the high heat and pressure of metamorphism. This team found that nanosphere inclusions of extraneous metallic lead (Pb) can confuse the dating technique, making the rock look older than it is. Writing in PNAS, they say:Zircon (ZrSiO4) is the most commonly used geochronometer, preserving age and geochemical information through a wide range of geological processes. However, zircon U–Pb geochronology can be affected by redistribution of radiogenic Pb, which is incompatible in the crystal structure. This phenomenon is particularly common in zircon that has experienced ultra-high temperature metamorphism, where ion imaging has revealed submicrometer domains that are sufficiently heterogeneously distributed to severely perturb ages, in some cases yielding apparent Hadean (>4 Ga) ages from younger zircons.The paper provides what they feel are safeguards to prevent erroneous dates. It appears, however, that this finding overthrows common assumptions used in the dating technique.The reliability of the oldest zircon ages, which include some reversely discordant analyses (i.e., with U–Pb ages older than 207Pb/206Pb ages), has been questioned based on evidence from ion imaging for disturbance of the U–Pb system. This is important because 207Pb/206Pb ages are generally considered to be more robust than U–Pb ages for older zircons. However, if radiogenic Pb has been decoupled from its parent U and not locally incorporated into the crystal lattice during an ancient geological event, when radiogenic 207Pb/206Pb values are significantly higher than at present, reverse discordance and spuriously old 207Pb/206Pb age estimates may result.In other words, the more lead in the crystal (“decoupled from its parent U”), the more a scientist might infer that it is billions of years old, when some of that lead got mixed in when a younger rock underwent metamorphism. Science Daily has a photograph of nanospheres of metallic lead embedded inside a zircon under the headline, “True ages of rocks might be distorted through Earth’s history.” Moreover, since the nanospheres are not uniformly distributed, the date could depend on the sample selected, like a biopsy missing the cancer. “The inhomogeneous distribution of lead in zircon might adulterate the ages measured with high-spatial resolution ion probe technique.”Update 4/13/15: Smithsonian scientists used zircons to date the formation of the Panama land bridge, according to Science Daily and Science Magazine (see full paper in Science). This is supposedly the time when North American animals could reach South America. The new date of 13-15 million years “could rewrite the geological history of the Americas,” Lizzie Wade writes in Science Magazine, because it is “more than 10 million years earlier than previously thought.” A lot of evolutionary weight is being placed on these zircons.In the ICR publication Acts & Facts, Dr. Vernon R. Cupps has been publishing a detailed analysis of how results can be corrupted in radiometric dating. He has shown numerous ways that deceptively old dates can be produced, depending on the assumptions used. The mathematical techniques are sound, but like with computer programs, wrong assumptions can make for garbage-in, garbage-out conclusions. Those interested may wish to study this new PNAS paper to see how often this problem occurs in practice. (Visited 58 times, 1 visits today)FacebookTwitterPinterestSave分享0
4 September 2012A new policy-orientated web portal on children’s rights, called Policy Action Network, or PAN: Children, was announced during a panel discussion on children in Cape Town on Monday.The portal – children.pan.org.za – is a partnership between the United Nations Children’s Fund (Unicef) and South Africa’s Human Sciences Research Council’s (HSRC).According to the HSRC, PAN: Children will provide high-quality, timely information which can be used to inform decision-making and policy.“It will strengthen the dialogue between the producers and the users of child-related research evidence to build networks between researchers and policy makers,” the HSRC said in a statement. “The aim is also to generate debates on key policy issues affecting children in South Africa.”The web portal is primarily targeted at South African policy makers and government officials involved in planning, implementation, monitoring and evaluation of policies and programmes relating to children, as well as academics and other research institutions working on issues related to child rights and their well-being.The knowledge-hub “will also be of value to civil society organisations, private sector and development sector professionals involved in the advancement of child rights,” the HSRC said. “Lastly, the hub will allow other countries with an interest in South African policy to easily access relevant information.”PAN: Children also aims to establish and maintain an up-to-date digital repository of the most credible publications available on child rights in South Africa.The information and resources available include advocacy initiatives and networks, case studies, case law, country studies, government policy and legislation, and other useful information.In addition, the portal will produce regular opinion pieces written by acknowledged research experts in the child rights arena, commenting on current debates and providing insight on policy development and practice.SAinfo reporter
zoom Monaco-based tanker owner Scorpio Tankers has received a commitment from Germany’s HSH Nordbank, one of the world’s biggest providers of shipping finance, for a loan facility to finance its two Medium Range (MR) product tankers.The loan in the amount of up to USD 34 million is expected to be used to refinance the existing indebtedness on the two tankers.Scorpio Tankers said that the availability is expected to be used to finance up to 60% of the fair market value of the vessels.The loan facility is subject to customary conditions precedent and the execution of definitive documentation.It has a final maturity of five years from the first drawdown date and bears interest at LIBOR plus a margin of 2.50% per annum.The remaining terms and conditions, including financial covenants, are similar to those set forth in the company’s 2016 Credit Facility, fully drawn in September 2016, and the aggregate proceeds of USD 288 million were used to refinance the existing indebtedness on sixteen MR product tankers.During the third quarter of 2016, Scorpio Tankers recorded a net loss of USD 27.1 million, compared to a net income of USD 85.3 million in the same period last year.The loss is primarily attributed to low Time Charter Equivalent (TCE) revenue that plunged to USD 114 million from USD 227.2 million on the year-on-year basis.
MONTREAL – Four men found in a shipping container at the Port of Montreal were granted release from detention on Friday as they await their refugee claim hearings.Canada Border Service Agency agents in Montreal found the four men from Georgia as they searched a container in the port on July 20.A security guard doing rounds at about 7 a.m. heard the men calling for help and saw a small white flag waving from a hole in the container, according to documents presented at the hearing.The men, aged between 30 and 40, were suffering from dehydration and authorities said they’d been in the container for some time.There is a publication ban on their identities and their reasons for coming to Canada.Immigration and Refugee Board of Canada member Francois Milo said the men have valid passports and no criminal records at a detention review hearing.He said they have been found eligible to make refugee claims and don’t seem to pose an undue flight risk.A lawyer for the men says they now all appear to be in good health.“They seemed to be doing very well physically, there were no health problems following that adventure,” Vincent Desbiens said after the hearing.Through an interpreter, the men agreed to provide an address, show up for hearings when summoned, and notify authorities if they leave Canada.The men will now await their hearings to learn if their asylum claims are accepted — a process that could take up to a year, according to Milo.