# Absolute dating of rock layer below

03-Oct-2019 08:40

An element is defined by the number of protons it contains. For carbon-14 decay, each carbon-14 atom loses an alpha particle. This is illustrated in Figure below and at the link below.[Insert a link to an animation of the decay of carbon-14 to nitrogen-14.] The decay of an unstable isotope to a stable element occurs at a constant rate. The decay rate is measured in a unit called the half-life.

All atoms of a given element contain the same number of protons. Atoms of an element with different numbers of neutrons are called isotopes. The half-life is the time it takes for half of a given amount of an isotope to decay.

We can do this by using the trilobite index fossil, because it appears in all three outcrops.

By correlating them, we now know that layers A, K, and Q are the same age.

The radiometric techniques that give absolute dating estimates are based on radioactive decay of elements such as uranium. Looking at how rock formations are structured, a geologist may be able to say which rock was developed in which layer in a particular order but not be able to determine that actual geologic age of the layers. Relative dispersion, sometimes called the coefficient of variation, is the result of dividing the st. by the mean, hence it is dimensionless (it may also be presented as a percentage).

Geologists also have radiometric methods for absolute dating based on radioactive decay of certain elements. So a low value of relative dispersion usually implies that the st. is small in comparison to the magnitude of the mean, as in a st. of 6cm for a mean of 4m would give a figure of 0.015 (1.5%) whereas with a mean of 40cm it would be 0.15 or 15%. However with measurements either side of zero and a mean close to zero the relative dispersion could be greater than 1.

INDEX FOSSILS ARE FOSSILS OR ORGANISMS THAT LIVED OVER A VERY LARGE AREA, BUT LIVED FOR A VERY SHORT TIME.

To find the oldest and youngest layers in the entire diagram, we first have to correlate the three outcrops.These fossils are very useful for us because we can use them to date the layers of rock that they are found in.