### UCSB Science Line

Could you also please explain further what radiometric dating is and the process to For example, a problem I have worked on involving the eruption of a volcano at When an unstable Uranium (U) isotope decays, it turns into an isotope of the . The most common isotopes used are uranium and uranium (there. Uranium-Lead dating is a radiometric dating method that uses the decay The four isotopes are uranium, uranium, lead, and lead Some of the classic problems with this kind of dating process include. Give examples of other isotopes used in radioactive dating. . Since U has a half-life of billion years, it takes that amount of time for half.

This fact helps with extracting the zircon out of the rock it was in [1]. Most radiometric daters prefer using zircon for these reasons, but it is not the only compound used for uranium-lead dating.

Some other compounds used that have zirconium are zirconoliteand badeleyite. Other compounds that do not contain zirconium but are commonly used for this method are titaniteand monazite. Since most radiometric daters prefer using zircon for this process, geologists often call uranium-lead dating zircon dating [1]. Problems With all radiometric dating processes, the accuracy of uranium-lead dating is called into question.

Some of the classic problems with this kind of dating process include what the process can really date, how far the radiometric process can date accurately, and the assumptions taken so the dating process works.

## Uranium–lead dating

One assumption is to use a worldview that uniformitarianism is accepted [3]. They use this equation to find the age of a rock: Where is the time from starting point, the original amount of uranium, the amount of uranium at the measurement, the original amount of lead, the amount of lead at the measurement, the rate uranium changes to lead, the average rate of loss and gain in the amount of lead, the average rate of loss and gain in the amount of uranium.

Limitations Uranium-Lead dating only works on igneous and metamorphic rocks because sedimentary layers contain small pieces of a other rock layers [3].

Like all radiometric dating methods, uranium-lead dating has a range that it works best. For uranium-lead has a range of 10 million to 4. This means that to begin with, any rock dated with this process will be in the 10's of millions [5].

Assumptions For Uranium - Lead dating to work, scientists have to make three assumptions. These assumptions are that the system being dated is a closed system ; at the beginning of the time period, there are no daughter isotopes present; and the rate of radioactive decay stays the same through the whole time period. Once all these assumptions are taken, the equation above simplifies to [4].

Without a closed system, uranium-lead dating, like all other radiometric dating methods, falls apart. Assuming a closed system means that nothing on the outside of the rock affected the sample.

### Apologetics Press - Problems with Radiometric Dating

This means that none of the parent or daughter isotope leaked in or out. It also implies that none of the factors that might affect the rate of the radioactive decay could not. This is an ideal concept that cannot happen. If the ages this dating process generates are true, it gets harder to assume that nothing on the outside of the sample has any effect on the system.

After a few million or billion years of a near-closed system, it will have a large error [6]. To find the age of a rock, a person trying to find it has to know the original amount of the parent isotope, and the original amount of the daughter isotope. The common assumption evolutionary scientists use is that the original amount was zero. This is not scientific because at the beginning of that rock, there were no scientific observers to measure original amount of daughter isotope, in this case that would be lead and lead [4].

In many cases, the daughter nuclide itself is radioactive, resulting in a decay chaineventually ending with the formation of a stable nonradioactive daughter nuclide; each step in such a chain is characterized by a distinct half-life. In these cases, usually the half-life of interest in radiometric dating is the longest one in the chain, which is the rate-limiting factor in the ultimate transformation of the radioactive nuclide into its stable daughter.

Isotopic systems that have been exploited for radiometric dating have half-lives ranging from only about 10 years e. It is not affected by external factors such as temperaturepressurechemical environment, or presence of a magnetic or electric field.

For all other nuclides, the proportion of the original nuclide to its decay products changes in a predictable way as the original nuclide decays over time.

This predictability allows the relative abundances of related nuclides to be used as a clock to measure the time from the incorporation of the original nuclides into a material to the present.

Accuracy of radiometric dating[ edit ] Thermal ionization mass spectrometer used in radiometric dating. The basic equation of radiometric dating requires that neither the parent nuclide nor the daughter product can enter or leave the material after its formation.

The possible confounding effects of contamination of parent and daughter isotopes have to be considered, as do the effects of any loss or gain of such isotopes since the sample was created.

It is therefore essential to have as much information as possible about the material being dated and to check for possible signs of alteration.

Alternatively, if several different minerals can be dated from the same sample and are assumed to be formed by the same event and were in equilibrium with the reservoir when they formed, they should form an isochron. This can reduce the problem of contamination. In uranium—lead datingthe concordia diagram is used which also decreases the problem of nuclide loss.

Finally, correlation between different isotopic dating methods may be required to confirm the age of a sample.

For example, the age of the Amitsoq gneisses from western Greenland was determined to be 3. The procedures used to isolate and analyze the parent and daughter nuclides must be precise and accurate. This normally involves isotope-ratio mass spectrometry. For instance, carbon has a half-life of 5, years. After an organism has been dead for 60, years, so little carbon is left that accurate dating cannot be established. On the other hand, the concentration of carbon falls off so steeply that the age of relatively young remains can be determined precisely to within a few decades.

Closure temperature If a material that selectively rejects the daughter nuclide is heated, any daughter nuclides that have been accumulated over time will be lost through diffusionsetting the isotopic "clock" to zero. The temperature at which this happens is known as the closure temperature or blocking temperature and is specific to a particular material and isotopic system.

These temperatures are experimentally determined in the lab by artificially resetting sample minerals using a high-temperature furnace. As the mineral cools, the crystal structure begins to form and diffusion of isotopes is less easy. At a certain temperature, the crystal structure has formed sufficiently to prevent diffusion of isotopes.

This temperature is what is known as closure temperature and represents the temperature below which the mineral is a closed system to isotopes.

Thus an igneous or metamorphic rock or melt, which is slowly cooling, does not begin to exhibit measurable radioactive decay until it cools below the closure temperature. The age that can be calculated by radiometric dating is thus the time at which the rock or mineral cooled to closure temperature.

This field is known as thermochronology or thermochronometry. The age is calculated from the slope of the isochron line and the original composition from the intercept of the isochron with the y-axis.

The equation is most conveniently expressed in terms of the measured quantity N t rather than the constant initial value No. The above equation makes use of information on the composition of parent and daughter isotopes at the time the material being tested cooled below its closure temperature. This is well-established for most isotopic systems. Plotting an isochron is used to solve the age equation graphically and calculate the age of the sample and the original composition.

Modern dating methods[ edit ] Radiometric dating has been carried out since when it was invented by Ernest Rutherford as a method by which one might determine the age of the Earth.

In the century since then the techniques have been greatly improved and expanded. The mass spectrometer was invented in the s and began to be used in radiometric dating in the s. It operates by generating a beam of ionized atoms from the sample under test. The ions then travel through a magnetic field, which diverts them into different sampling sensors, known as " Faraday cups ", depending on their mass and level of ionization.

On impact in the cups, the ions set up a very weak current that can be measured to determine the rate of impacts and the relative concentrations of different atoms in the beams. Uranium—lead dating method[ edit ] Main article: Uranium—lead dating A concordia diagram as used in uranium—lead datingwith data from the Pfunze BeltZimbabwe. This scheme has been refined to the point that the error margin in dates of rocks can be as low as less than two million years in two-and-a-half billion years.

Zircon has a very high closure temperature, is resistant to mechanical weathering and is very chemically inert. Zircon also forms multiple crystal layers during metamorphic events, which each may record an isotopic age of the event.

This can be seen in the concordia diagram, where the samples plot along an errorchron straight line which intersects the concordia curve at the age of the sample. Samarium—neodymium dating method[ edit ] Main article: Samarium—neodymium dating This involves the alpha decay of Sm to Nd with a half-life of 1. Accuracy levels of within twenty million years in ages of two-and-a-half billion years are achievable.

### Uranium-Lead dating - CreationWiki, the encyclopedia of creation science

Potassium—argon dating This involves electron capture or positron decay of potassium to argon Potassium has a half-life of 1. Rubidium—strontium dating method[ edit ] Main article: Rubidium—strontium dating This is based on the beta decay of rubidium to strontiumwith a half-life of 50 billion years. This scheme is used to date old igneous and metamorphic rocksand has also been used to date lunar samples.