Explain the principle of radioactive dating

Radiometric dating , radioactive dating or radioisotope dating is a technique used to date materials such as rocks or carbon , in which trace radioactive impurities were selectively incorporated when they were formed. The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay. Together with stratigraphic principles , radiometric dating methods are used in geochronology to establish the geologic time scale. By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change. Radiometric dating is also used to date archaeological materials, including ancient artifacts. Different methods of radiometric dating vary in the timescale over which they are accurate and the materials to which they can be applied.

Radiocarbon Dating Principles

About 75 years ago, Williard F. Libby, a Professor of Chemistry at the University of Chicago, predicted that a radioactive isotope of carbon, known as carbon, would be found to occur in nature. Since carbon is fundamental to life, occurring along with hydrogen in all organic compounds, the detection of such an isotope might form the basis for a method to establish the age of ancient materials. Working with several collaboraters, Libby established the natural occurrence of radiocarbon by detecting its radioactivity in methane from the Baltimore sewer.

In contrast, methane made from petroleum products had no measurable radioactivity. Carbon is produced in the upper atmosphere when cosmic rays bombard nitrogen atoms. The ensuing atomic interactions create a steady supply of c14 that rapidly diffuses throughout the atmosphere. Plants take up c14 along with other carbon isotopes during photosynthesis in the proportions that occur in the atmosphere; animals acquire c14 by eating the plants or other animals.

During the lifetime of an organism, the amount of c14 in the tissues remains at an equilibrium since the loss through radioactive decay is balanced by the gain through uptake via photosynthesis or consumption of organically fixed carbon. However, when the organism dies, the amount of c14 declines such that the longer the time since death the lower the levels of c14 in organic tissue. This is the clock that permits levels of c14 in organic archaeological, geological, and paleontological samples to be converted into an estimate of time.

The measurement of the rate of radioactive decay is known as its half-life, the time it takes for half of a sample to decay. This means that half of the c14 has decayed by the time an organism has been dead for years, and half of the remainder has decayed by 11, years after death, etc. The diminishing levels via decay means that the effective limit for using c14 to estimate time is about 50, years.

After this time, there is little if any c14 left. However, to avoid confusion all radiocarbon laboratories continue to use the half-life calculated by Libby, sometimes rounding it to years. Any organic material that is available in sufficient quantity can be prepared for radiocarbon dating. Modern AMS accelerator mass spectroscopy methods require tiny amounts, about 50 mg.

AMS technology has allowed us to date very small samples such as seeds that were previously undatable. Since there are practical limits to the age range of the method, most samples must be younger than 50, years and older than years. Most samples require chemical pre-treatment to ensure their purity or to recover particular components of the material.

The objective of pre-treatment is to ensure that the carbon being analyzed is native to the sample submitted for dating. Pre-treatment seeks to remove from the sample any contaminating carbon that could yield an inaccurate date. Acids may be used to eliminate contaminating carbonates. Bases may be used to remove contaminating humic acids.

Some types of samples require more extensive pre-treatment than others, and these methods have evolved over the first 50 years of radiocarbon dating. For example, it was once standard practice to simply burn whole bones, but the results were eventually seen to be unreliable. Chemical methods for separating the organic collagen from the inorganic apatite components of bone created the opportunity to date both components and compare the results.

The collagen fraction usually yields more reliable dates than the apatite fraction see Dates on bones. In addition to various pre-treatments, the sample must be burned and converted to a form suitable for the counter. The sample must be destroyed in order to measure its c14 content. The first measurements of radiocarbon were made in screen-walled Geiger counters with the sample prepared for measurement in a solid form.

These so-called "solid-carbon" dates were soon found to yield ages somewhat younger than expected, and there were many other technical problems associated with sample preparation and the operation of the counters. Gas proportional counters soon replaced the solid-carbon method in all laboratories, with the samples being converted to gases such as carbon dioxide, carbon disulfide, methane, or acetylene.

Many laboratories now use liquid scintillation counters with the samples being converted to benzene. All of these counter types measure the C content by monitering the rate of decay per unit time. A more recent innovation is the direct counting of c14 atoms by accelerator mass spectrometers AMS. The sample is converted to graphite and mounted in an ion source from which it is sputtered and accelerated through a magnetic field. Targets tuned to different atomic weights count the number of c12, c13, and c 14 atoms in a sample.

Many samples reported as "modern" have levels of radioactivity that are indistinguishable from modern standards such as oxalic acid. Due to contamination from bomb testing, some samples are even more radioactive than the modern standards. Other very young samples may be given maximum limits, such as 40, years. The very old samples have such low radioactivity that they cannot be distinguished reliably from the background radiation. Very few laboratories are able to measure ages of more than 40, years.

Several aspects of radiocarbon measurement have built-in uncertainties. Every laboratory must factor out background radiation that varies geographically and through time. The variation in background radiation is monitered by routinely measuring standards such as anthracite coal , oxalic acid, and certain materials of well-known age. The standards offer a basis for interpreting the radioactivity of the unknown sample, but there is always a degree of uncertainty in any measurement.

Since decay-counting records random events per unit time, uncertainty is an inherent aspect of the method. Most laboratories consider only the counting statistics, i. However, some laboratories factor in other variables such as the uncertainty in the measurement of the half-life. Some laboratories impose a minimum value on their error terms. Most laboratories use a 2-sigma criterion to establish minimum and maximum ages. In keeping with its practice of quoting 2-sigma errors for so-called finite dates, the Geological Survey of Canada uses a 4-sigma criterion for non-finite dates.

The first radiocarbon dates reported had their ages calculated to the nearest year, expressed in years before present BP. It was soon apparent that the meaning of BP would change every year and that one would need to know the date of the analysis in order to understand the age of the sample. To avoid confusion, an international convention established that the year A.

Thus, BP means years before A. Some people continue to express radiocarbon dates in relation to the calendar by subtracting from the reported age. This practice is incorrect, because it is now known that radiocarbon years are not equivalent to calendar years. To express a radiocarbon date in calendar years it must be normalized, corrected as needed for reservoir effects, and calibrated. Radiocarbon dates can be obtained only from organic materials, and many archaeological sites offer little or no organic preservation.

Even if organic preservation is excellent, the organic materials themselves are not always the items of greatest interest to the archaeologist. However, their association with cultural features such as house remains or fireplaces may make organic substances such as charcoal and bone suitable choices for radiocarbon dating. A crucial problem is that the resulting date measures only the time since the death of a plant or animal, and it is up to the archaeologist to record evidence that the death of the organism is directly related to or associated with the human activities represented by the artifacts and cultural features.

Many sites in Arctic Canada contain charcoal derived from driftwood that was collected by ancient people and used for fuel. A radiocarbon date on driftwood may be several centuries older than expected, because the tree may have died hundreds of years before it was used to light a fire. In forested areas it is not uncommon to find the charred roots of trees extending downward into archaeological materials buried at deeper levels in a site. Charcoal from such roots may be the result of a forest fire that occurred hundreds of years after the archaeological materials were buried, and a radiocarbon date on such charcoal will yield an age younger than expected.

Bone is second only to charcoal as a material chosen for radiocarbon dating. It offers some advantages over charcoal. For example, to demonstrate a secure association between bones and artifacts is often easier than to demonstrate a definite link between charcoal and artifacts. However, bone presents some special challenges, and methods of pre-treatment for bone, antler, horn and tusk samples have undergone profound changes during the past 50 years.

Initially most laboratories merely burned whole bones or bone fragments, retaining in the sample both organic and inorganic carbon native to the bone, as well as any carbonaceous contaminants that may have been present. Indeed, it was believed, apparently by analogy with elemental charcoal, that bone was suitable for radiocarbon dating "when heavily charred" Rainey and Ralph, Dates on bone produced by such methods are highly suspect.

They are most likely to err on the young side, but it is not possible to predict their reliability. The development of chemical methods to isolate carbon from the organic and inorganic constituents of bone was a major step forward. Berger, Horney, and Libby published a method of extracting the organic carbon from bone.

Many laboratories adopted this method which produced a gelatin presumed to consist mainly of collagen. This method is called "insoluble collagen extraction" in this database. Longin showed that collagen could be extracted in a soluble form that permitted a greater degree of decontamination of the sample. Haynes presented a method of extracting the inorganic carbon from bone.

This method was considered suitable for use in areas where collagen is rarely or poorly preserved in bones. Subsequent research cast doubt on the reliability of this method. Hassan and others ; Hassan and Ortner, showed that the inorganic carbon contained in bone apatite is highly susceptible to contamination by either younger or older carbon in the burial environment. It now appears that insoluble collagen extractions usually err on the young side, if at all Rutherford and Wittenberg, , whereas bone apatite can produce ages either older or younger than the true age, often by a considerable margin.

Ongoing research has continued to refine methods of extracting collagen, especially from small samples destined for AMS dating. For example, D. Stafford ; Stafford, et al. Hedges and Van Klinken review other recent advances in the pre-treatment of bone. One of the initial assumptions of the method was that the rate of production of radiocarbon is constant.

This assumption is now known to be incorrect, meaning that radiocarbon years are not equivalent to calendar years. International collaboration by many laboratories has produced increasingly refined calibration curves. The latest calibration dataset, known as INTCAL98, links the dated tree-ring record to the uranium-thorium dating of corals and finally to terrestrial varve chronologies to achieve calibration over the interval , years.

CALIB 4. Some studies can be conducted entirely in terms of radiocarbon years. Other studies, such as those focused on rates of change, may require more or less precise calibrations. Land plants and the food chains they support acquire most of their carbon from the atmosphere, whereas marine food chains acquire carbon mainly from the oceans.

Carbon dating is about some basic idea behind the remaining radioactive decay. Petrucci, and an axiom that discuss the principles such as absolute isotopic. Relative Dating with Fossils: Index Fossils as Indicators of Time. Radiometric Dating: Methods, Uses & the Significance of Half-Life. What is Relative Dating?.

Geologist Ralph Harvey and historian Mott Greene explain the principles of radiometric dating and its application in determining the age of Earth. As the uranium in rocks decays, it emits subatomic particles and turns into lead at a constant rate. Measuring the uranium-to-lead ratios in the oldest rocks on Earth gave scientists an estimated age of the planet of 4. Segment from A Science Odyssey:

Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4. Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free.

Explain the principle behind radioactive dating. Spread the love.

How Does Carbon Dating Work

Teach the Earth the portal for Earth Education. Outline of lecture topics and hands-on activities for introducing radiometric dating. Introduce the concept of time and how we measure it. Have students think about how a calendar works: Why are months so variable in length?

radiometric dating

About 75 years ago, Williard F. Libby, a Professor of Chemistry at the University of Chicago, predicted that a radioactive isotope of carbon, known as carbon, would be found to occur in nature. Since carbon is fundamental to life, occurring along with hydrogen in all organic compounds, the detection of such an isotope might form the basis for a method to establish the age of ancient materials. Working with several collaboraters, Libby established the natural occurrence of radiocarbon by detecting its radioactivity in methane from the Baltimore sewer. In contrast, methane made from petroleum products had no measurable radioactivity. Carbon is produced in the upper atmosphere when cosmic rays bombard nitrogen atoms. The ensuing atomic interactions create a steady supply of c14 that rapidly diffuses throughout the atmosphere. Plants take up c14 along with other carbon isotopes during photosynthesis in the proportions that occur in the atmosphere; animals acquire c14 by eating the plants or other animals. During the lifetime of an organism, the amount of c14 in the tissues remains at an equilibrium since the loss through radioactive decay is balanced by the gain through uptake via photosynthesis or consumption of organically fixed carbon. However, when the organism dies, the amount of c14 declines such that the longer the time since death the lower the levels of c14 in organic tissue.

Radiocarbon dating is a method that provides objective age estimates for carbon-based materials that originated from living organisms. The impact of the radiocarbon dating technique on modern man has made it one of the most significant discoveries of the 20th century.

Petrology Tulane University Prof. Stephen A.

Radiometric Dating

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Radiometric dating

A process for determining the age of an object by measuring the amount of a given radioactive material it contains. If one knows how much of this radioactive material was present initially in the object by determining how much of the material has decayed , and one knows the half-life of the material, one can deduce the age of the object. The simple days of immediately understanding what SWF means are far behind us. Online dating has made acronyms more inscrutable—and more fun—than ever. Take our quiz and find out. We hope this made it a little bit easier to navigate those stormy dating waters. First recorded in —

) Explain the principle of radioactive dating​

It is an accurate way to date specific geologic events. This is an enormous branch of geochemistry called Geochronology. There are many radiometric clocks and when applied to appropriate materials, the dating can be very accurate. As one example, the first minerals to crystallize condense from the hot cloud of gasses that surrounded the Sun as it first became a star have been dated to plus or minus 2 million years!! That is pretty accurate!!!

Dating Rocks and Fossils Using Geologic Methods

Radiometric dating is a means of determining the "age" of a mineral specimen by determining the relative amounts present of certain radioactive elements. By "age" we mean the elapsed time from when the mineral specimen was formed. Radioactive elements "decay" that is, change into other elements by "half lives. The formula for the fraction remaining is one-half raised to the power given by the number of years divided by the half-life in other words raised to a power equal to the number of half-lives. If we knew the fraction of a radioactive element still remaining in a mineral, it would be a simple matter to calculate its age by the formula. To determine the fraction still remaining, we must know both the amount now present and also the amount present when the mineral was formed. Contrary to creationist claims, it is possible to make that determination, as the following will explain:.

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9.6 Radioactive dating
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