Sometimes different methods used on the same rock produce different ages. Furthermore, the same method can produce different ages on different parts of the same rock. Sometimes these are close but other times they are very different. Isotopic Fractionation Isotopic Fractionation is a physical separation of isotopes and a non-radioactive source of isotope ratios. It can be caused by heating and cooling, water flow, contact between high and low concentration magma and just normal molecular motion. Evidence for Isotopic Fractionation does show up in isotopic data so it is a factor that needs to be considered. Water flow through rocks is important because all parent substances and many daughter substances are water soluble.
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Single grain pyrite Rb—Sr dating of the Linglong gold deposit, eastern China This study employs the single grain pyrite Rb—Sr technique to date mineralization, using the exam The gold deposits in this area are interpreted to have a consistent spatial—temporal relationship with widespread Late Jurassic—Early Cretaceous magmatism in eastern China, likely related to lithospheric thinning around Ma.
Four pyrite samples from veins of different mineralization stages give an average isochron age of Analyses of one quartz and two sericite samples yield isochron ages between Ma and Ma. Hence, the successful attempt of the single grain Rb—Sr technique of pyrite, which occurs as a common mineral phase in orebodies and is genetically related to the mineralization, has great potential for precise geochronology of hydrothermal mineral deposits.
Rb-Sr (and Pb-Pb) isochron dating has played a major role in geochronology. Rb-Sr and Pb-Pb whole-rock isochrons and multi-grain zircon U-Pb ages By the beginning of the s, dating of whole rocks with the help of Rb-Sr isochrons had come into gen-eral .
Exploring the wonders of geology in response to young-Earth claims Please read my guidelines and background posts before proceeding! Wednesday, March 2, Inventing the isochron: Steve Austin, Andrew Snelling, and the Cardenas Basalts of the Grand Canyon At the beginning of the year, I reviewed an article that cited anomalously old radiometric dates for historical lava flows to argue against the validity of the Potassium-Argon K-Ar dating method. Therein, I proposed that young-Earth authors ubiquitously employ the following approach in their discussions of radiometric dating: Steve Austin and Dr.
While there are numerous natural processes that can serve as clocks, there are also many natural processes that can reset or scramble these time-dependent processes and introduce uncertainties. To try to set a reasonable bound on the age, we could presume that the Earth formed at the same time as the rest of the solar system. If the small masses that become meteorites are part of that system, then a measurement of the solidification time of those meteorites gives an estimate of the age of the Earth.
May 30, · For Weekeroo Station only the sole Hf-W isochron age matches the “target” age, whereas five of the six Rb-Sr isochron ages are much younger, and the other is older, plus the one Sm-Nd isochron.
The Radiometric Dating Game Radiometric dating methods estimate the age of rocks using calculations based on the decay rates of radioactive elements such as uranium, strontium, and potassium. On the surface, radiometric dating methods appear to give powerful support to the statement that life has existed on the earth for hundreds of millions, even billions, of years. We are told that these methods are accurate to a few percent, and that there are many different methods.
We are told that of all the radiometric dates that are measured, only a few percent are anomalous. This gives us the impression that all but a small percentage of the dates computed by radiometric methods agree with the assumed ages of the rocks in which they are found, and that all of these various methods almost always give ages that agree with each other to within a few percentage points. Since there doesn’t seem to be any systematic error that could cause so many methods to agree with each other so often, it seems that there is no other rational conclusion than to accept these dates as accurate.
However, this causes a problem for those who believe based on the Bible that life has only existed on the earth for a few thousand years, since fossils are found in rocks that are dated to be over million years old by radiometric methods, and some fossils are found in rocks that are dated to be billions of years old. If these dates are correct, this calls the Biblical account of a recent creation of life into question.
After study and discussion of this question, I now believe that the claimed accuracy of radiometric dating methods is a result of a great misunderstanding of the data, and that the various methods hardly ever agree with each other, and often do not agree with the assumed ages of the rocks in which they are found. I believe that there is a great need for this information to be made known, so I am making this article available in the hopes that it will enlighten others who are considering these questions.
Even the creationist accounts that I have read do not adequately treat these issues. At the start, let me clarify that my main concern is not the age of the earth, the moon, or the solar system, but rather the age of life, that is, how long has life existed on earth. Many dating methods seem to give about the same ages on meteorites. Thus radiometric dating methods appear to give evidence that the earth and meteorites are old, if one accepts the fact that decay rates have been constant.
Several Christian ministries promote the idea that the earth is less than 10, years old, which they say comes from the Bible. In reality, the Bible makes no claim as to the age of the earth, although it does establish a minimum age. This page examines some of the history of the controversy—what the Bible actually says and does not say—and the scientific evidence surrounding the age of the earth. Age of the earth according to the Bible The following is a summary of the biblical evidence presented on this website regarding the age of the earth.
Seven Bonneterre and Davis Formation glauconite samples from the Magmont mine area, Viburnum Trend, southeast Missouri, yield a + or – m.y. Rb-Sr isochron with an initial 87 Sr/ 86 Sr ratio of + or – (2 sigma).
The isotopes[ edit ] There are three isotopes used in Rb-Sr dating. It produces the stable daughter isotope 87Sr strontium by beta minus decay. The third isotope we need to consider is 86Sr, which is stable and is not radiogenic , meaning that in any closed system the quantity of 86Sr will remain the same. As rubidium easily substitutes chemically for potassium, it can be found doing so in small quantities in potassium-containing minerals such as biotite , potassium feldspar , and hornblende.
The quantity will be small because there is much more potassium than rubidium in the Universe. But there is no reason at all to suppose that there was no 87Sr present initially. When we produced the formula for K-Ar dating , it was reasonable enough to think that there was little to no argon present in the original state of the rock, because argon is an inert gas, does not take part in chemical processes, and so in particular does not take part in mineral formation. Strontium, on the other hand, does take part in chemical reactions, and can substitute chemically for such elements as calcium, which is commonly found in igneous rocks.
So we have every reason to think that rocks when they form do incorporate strontium, and 87Sr in particular. The isochron diagram[ edit ] However, there is still a way to extract a date from the rock.
Age of the Earth
The initial ratio has particular importance for studying the chemical evolution of the Earth’s mantle and crust, as we discussed in the section on igneous rocks. K-Ar Dating 40K is the radioactive isotope of K, and makes up 0. Since K is one of the 10 most abundant elements in the Earth’s crust, the decay of 40K is important in dating rocks. But this scheme is not used because 40Ca can be present as both radiogenic and non-radiogenic Ca.
Note that this is not always true.
in rubidium-strontium (Rb-Sr) dating, 86Sr in a sample will serve as the stable non-radio-genic (see equation 8). For purposes of iso-tope analysis, 87Sr/86Sr ratios are measured. Part Two: Radiometric Dating: Mineral, Isochron and Concordia Methods isochron and concordia.
Clearly visible in the canyon walls are the light-colored granites, such as the Zoroaster Granite, which are stark against the darker, folded strata of the Vishnu Schist and the other metamorphic rock units of the Granite Gorge Metamorphic Suite1 see lowest purple and green shading in diagram. These are former sedimentary and volcanic strata that have been transformed by heat and pressure, possibly during the intense upheavals when the dry land was formed on Day 3 of Creation Week.
These were originally basalt lava flows several meters to tens of meters thick. In some outcrops pillow structures have been preserved, testimony to the basalt lavas having originally erupted and flowed under water onto the Creation Week ocean floor. Metamorphic rocks are not always easy to date using radio-isotopes. Results obtained usually signify the “date” of the metamorphism, but they may also yield the “age” of the original volcanic or sedimentary rock.
The “age” or “date” is calculated from the amount of the daughter isotope produced by radioactive decay of the parent isotope.
Not only are their ages similar, but the direction of magnetization in the rocks is also identical and indicates that Oslo, Norway was located at about 30 degrees south at the time. This is an important consideration. In order to refute the ages, ye-creationists must not only explain how three different isotopic systems with different decay constantsa and chemical behavior all gave the same age and the same magnetic direction. It is also not trivial that the magnetic direction in these rocks indicates that Norway has moved northward following the emplacement of these rocks.
The Madagascar results are equally intriguing since they are from two regions on the island. These basalts and gabbros are thought by conventional geologists to have formed as Madagascar moved over the Marion hotspot during the Cretaceous.
THREE-SYSTEM ISOTOPIC STUDY OF LUNAR NORITE RB-SR RESULTS. J. sistent with the observation that the young Rb-Sr isochron determined for is concordant with the Ar-Ar age of . Therefore, provided the Rb-Sr the age of the disturbed isochron can be interpreted as dating the Serenitatis impact event .
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Historical Geology/Rb-Sr dating
References Generic Radiometric Dating The simplest form of isotopic age computation involves substituting three measurements into an equation of four variables, and solving for the fourth. The equation is the one which describes radioactive decay: The variables in the equation are: Pnow – The quantity of the parent isotope that remains now. This is measured directly. Porig – The quantity of the parent isotope that was originally present.
Re-evaluation of the age of Canadian dike swarms using Rb–Sr whole-rock data give the following results:Detailed studies of the Matachewan dike swarm show that in most cases Rb–Sr mineral isochron age values from individual samples are concordant with the Rb–Sr whole-rock age values for the dike swarm as a whole and are clearly greater than K–Ar age values on the same material.
What about isochron discordance? Based on the consistency of the discordance from this specimen a flood gabbro and others, infer the processes which led to the distribution of isotopes” taken from ICR , see link above ” I want to call your attention to several issues regarding their proposal. The first is that the RATE Group has pre-determined that the sample will be discordant or, in this case will not produce an isochron. Why even do the experiment?
No doubt it will produce an imprecise alignment of minerals and whole rocks because of the sample they chose1. Why did they choose a flood gabbro? There are a number of ways to produce bad data in geochronology1,2. The easiest is to apply the wrong method to the wrong rocks. Both methods rely on the presence of abundant K-bearing minerals Rb substitutes for K in many minerals due to their similar ionic radii and gabbros do not typically contain an abundance of K-bearing minerals1.
Measurements of lunar analogs like the Duluth Gabbro are a proof of concept for in situ dating of rocks on the Moon to constrain lunar history. Methods Using the laser ablation resonance ionization mass spectrometer we ablated hundreds of locations on a sample, and at each one measured the relative abundances of the isotopes of Rb and Sr. A delay between the resonant photoionization processes separates the elements in time, eliminating the potential interference between 87Rb and 87Sr.
Both these results agree with the age determined by Faure et al.
The 87 Rb/ 86 Sr and 87 Sr/ 86 Sr ratios are thought to be influenced only by radioactive decay of 87 Rb into 87 Sr. The whole theory of isochron dating is based, and dependent, on .
The two elements are joined in a parent—daughter relationship by the alpha decay of Sm to Nd with a half-life of 1. Some of the Sm may itself have originally been produced through alpha-decay from Gd , which has a half-life of 1. To find the date at which a rock or group of rocks formed one can use the method of isochron dating. From the slope of the “isochron” line through these points the date of formation can be determined. Alternatively, one can assume that the material formed from mantle material which was following the same path of evolution of these ratios as chondrites , and then again the time of formation can be calculated see The CHUR model.
Samarium is accommodated more easily into mafic minerals, so a mafic rock which crystallises mafic minerals will concentrate neodymium in the melt phase relative to samarium. Thus, as a melt undergoes fractional crystallization from a mafic to a more felsic composition, the abundance of Sm and Nd changes, as does the ratio between Sm and Nd.