# How does radioactive dating of rocks work

### BBC - GCSE Bitesize: Radioactive dating

All rocks and minerals contain tiny amounts of these radioactive elements. Radioactive decay occurs at a constant rate, specific to each radioactive isotope. Could you also please explain further what radiometric dating is and the of the parent to daughter then can be used to back-calculate the age of that rock. . Based on astronomical models of how stars work, we also believe the Sun to be. Radiometric dating (often called radioactive dating) is a technique used to date materials such as rocks or carbon, usually based on a.

Usually it involves using more than one sample from a given rock. It is done by comparing the ratios of parent and daughter isotopes relative to a stable isotope for samples with different relative amounts of the parent isotope.

From this one can determine how much of the daughter isotope would be present if there had been no parent isotope. This is the same as the initial amount it would not change if there were no parent isotope to decay.

## Radiometric dating

Figures 4 and 5 [in Wiens' article], and the accompanying explanation, tell how this is done most of the time. There are only a few different dating methods. There are actually many more methods out there. Well over forty different radiometric dating methods are in use, and a number of non-radiogenic methods not even mentioned here.

A young-Earth research group reported that they sent a rock erupted in from Mount Saint Helens volcano to a dating lab and got back a potassium-argon age of several million years. This shows we should not trust radiometric dating. There are indeed ways to "trick" radiometric dating if a single dating method is improperly used on a sample. Anyone can move the hands on a clock and get the wrong time.

Likewise, people actively looking for incorrect radiometric dates can in fact get them. Geologists have known for over forty years that the potassium-argon method cannot be used on rocks only twenty to thirty years old. Publicizing this incorrect age as a completely new finding was inappropriate. The reasons are discussed in the Potassium-Argon Dating section [of Wiens' article].

Be assured that multiple dating methods used together on igneous rocks are almost always correct unless the sample is too difficult to date due to factors such as metamorphism or a large fraction of xenoliths. Different dating techniques usually give conflicting results. This is not true at all. The fact that dating techniques most often agree with each other is why scientists tend to trust them in the first place. Nearly every college and university library in the country has periodicals such as Science, Nature, and specific geology journals that give the results of dating studies.

The public is usually welcome to and should!

**9.6 Radioactive dating (Nuclear chemistry) (Chemistry - Class 11 & Class 12)**

So the results are not hidden; people can go look at the results for themselves. Over a thousand research papers are published a year on radiometric dating, essentially all in agreement. Besides the scientific periodicals that carry up-to-date research reports, [there are] textbooks, non-classroom books, and web resources.

## How do geologists use carbon dating to find the age of rocks?

Anomalies As noted above, creationists make great hay out of "anomalies" in radiometric dating. It is true that some "anomalies" have been observed, although keep in mind that these have been identified by professional scientists in published literature, not by creationists or others outside of peer-reviewed scientific literature.

First of all, many of these claimed "anomalies" are completely irrelevant to the central issue of whether the Earth is many millions of years old. This is certainly true when errors are in the range of a few percent in specimens many millions of years old.

This is also true of anomalies noted in carbon dates. Carbon dating cannot be used to date anything older than about 50, years, since the carbon half life is only years. For additional discussion, see Radiocarbon dating. In any event, it is important to keep these anomalies in perspective. For example, out of literally tens of thousands of dates measured using the rubidium-strontium dating scheme see description of the Rb-Sr scheme in Agesonly about 30 cases have been noted where the individual data values initially appeared to lie nearly on a straight line as is requiredbut the result was later found to be significantly in error.

And each of these 30 cases is fairly well understood -- none of these is truly "mysterious" [ Wien ].

Anomalies and other objections that have been raised by creationists are dealt with in detail in Roger Wiens' article [ Wien ], Mark Isaak's book [ Isaakpg. A detailed response to other claims of scientific evidence for a young Earth is given by Matthew Tiscareno [ Tiscareno ]. Radioactive isotopes and the age of the Earth Until recently, only a large scientific laboratories could afford mass spectrometers, which are the principal tool used to measure dates of rock samples.

But recently the prices of these devices have dropped to levels that even amateur meteorite hunters and others can afford. Used mass spectrometers are currently available at eBay. Some have said that the last of the flat-earth believers did not give up until they could hold GPS receivers in their hand that give their latitude-longitude position.

Will skeptics of old-earth geology wait until mass spectrometers are in every home before finally conceding that the Earth is older than years?

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.

### What Is Radioactive Dating, and How Does It Work?

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.

### UCSB Science Line

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. Do you believe radiometric dating is an accurate way to date the earth? Why or why not?

Could you also please explain further what radiometric dating is and the process to use it? 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!!! Other events on earth can be dated equally well given the right minerals. For example, a problem I have worked on involving the eruption of a volcano at what is now Naples, Italy, occurred years ago with a plus or minus of years.

Yes, radiometric dating is a very accurate way to date the Earth. We know it is accurate because radiometric dating is based on the radioactive decay of unstable isotopes. For example, the element Uranium exists as one of several isotopes, some of which are unstable.

When an unstable Uranium U isotope decays, it turns into an isotope of the element Lead Pb. We call the original, unstable isotope Uranium the "parent", and the product of decay Lead the "daughter". From careful physics and chemistry experiments, we know that parents turn into daughters at a very consistent, predictable rate.

For an example of how geologists use radiometric dating, read on: A geologist can pick up a rock from a mountainside somewhere, and bring it back to the lab, and separate out the individual minerals that compose the rock.

They can then look at a single mineral, and using an instrument called a mass spectrometer, they can measure the amount of parent and the amount of daughter in that mineral. The ratio of the parent to daughter then can be used to back-calculate the age of that rock. The reason we know that radiometric dating works so well is because we can use several different isotope systems for example, Uranium-Lead, Lutetium-Halfnium, Potassium-Argon on the same rock, and they all come up with the same age.

This gives geologists great confidence that the method correctly determines when that rock formed. Hope that helps, and please ask if you'd like more details! I think that I will start by answering the second part of your question, just because I think that will make the answer to the first question clearer.