# Why is 238 used for dating rocks

### Uranium–uranium dating | serwis-reklam.info

Some of the isotopes used for this purpose are uranium, uranium and potassium, each of which has a half-life of more than a million years. Boltwood explained that by studying a rock containing uranium, one can billion years, so it can be used to date rocks as young as 50, years old. Uranium–lead dating, abbreviated U–Pb dating, is one of the oldest and most refined of the radiometric dating schemes. It can be used to date rocks that formed and crystallised from about 1 million However, use of a single decay scheme (usually U to Pb) leads to the U–Pb isochron dating method, analogous to.

For example, during the s, when many above-ground tests of nuclear weapons occurred, the earth was littered by cesium half-life of By collecting samples of sediment, scientists are able to obtain various types of kinetic information based on the concentration of cesium found in the samples. Lead, a naturally occurring radionuclide with a half-life of Radium, a grandparent of lead, decays to radon, the radioactive gas that can be found in some basements. Because it is a gas, radon exists in the atmosphere.

Radon decays to polonium, which attaches to particles in the atmosphere and is consequently rained out—falling into and traveling through streams, riversand lakes.

Radioactive dating has proved to be an invaluable tool and has been used in many scientific fields, including geologyarcheology, paleoclimatology, atmospheric science, oceanographyhydrologyand biomedicine.

This method of dating has also been used to study artifacts that have received a great deal of public attention, such as the Shroud of Turin, the Dead Sea Scrolls, Egyptian tombs, and Stonehenge. Since the discovery of radioactive dating, there have been several improvements in the equipment used to measure radioactive residuals in samples.

### How are C and U dating used together in order to determine fossil ages? | Socratic

For example, with the invention of accelerator mass spectometry, scientists have been able to date samples very accurately. Content on this website is from high-quality, licensed material originally published in print form. You can always be sure you're reading unbiased, factual, and accurate information.

To determine the ages of these specimens, scientists need an isotope with a very long half-life.

- Uranium–lead dating
- Dating rocks
- Radiometric dating

Some of the isotopes used for this purpose are uranium, uranium and potassium, each of which has a half-life of more than a million years. Unfortunately, these elements don't exist in dinosaur fossils themselves. Each of them typically exists in igneous rock, or rock made from cooled magma.

**How Can Radioactive Dating Be Used To Determine The Age Of Rocks?**

Fossils, however, form in sedimentary rock -- sediment quickly covers a dinosaur's body, and the sediment and the bones gradually turn into rock.

But this sediment doesn't typically include the necessary isotopes in measurable amounts. Fossils can't form in the igneous rock that usually does contain the isotopes. The extreme temperatures of the magma would just destroy the bones. 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.

## How are C-14 and U-238 dating used together in order to determine fossil ages?

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.

### Dating Sedimentary Rock - How Do Scientists Determine the Age of Dinosaur Bones? | HowStuffWorks

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.

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.