Dinosaur bones, on the other hand, are millions of years old -- some fossils are billions of years old. To determine the ages of these specimens, scientists need an isotope with a very long half-life. 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.
18.5D: Carbon Dating and Estimating Fossil Age
Each of them typically exists in igneous rock, or rock made from cooled magma. 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.
Carbon, Radiometric Dating - CSI
So to determine the age of sedimentary rock layers, researchers first have to find neighboring layers of Earth that include igneous rock, such as volcanic ash. Potassium is another radioactive element naturally found in your body and has a half-life of 1. The use of various radioisotopes allows the dating of biological and geological samples with a high degree of accuracy. However, radioisotope dating may not work so well in the future. Anything that dies after the s, when Nuclear bombs , nuclear reactors and open-air nuclear tests started changing things, will be harder to date precisely.
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Earthquakes on the Mississippi: The New Madrid Seismic Zone. Stratigraphy is the science of understanding the strata, or layers, that form the sedimentary record. Strata are differentiated from each other by their different colors or compositions and are exposed in cliffs, quarries, and river banks.
These rocks normally form relatively horizontal, parallel layers, with younger layers forming on top. Because rock sequences are not continuous, but may be broken up by faults or periods of erosion, it is difficult to match up rock beds that are not directly adjacent.
The layers of sedimentary rock, or strata, can be seen as horizontal bands of differently colored or differently structured materials exposed in this cliff. The deeper layers are older than the layers found at the top, which aids in determining the relative age of fossils found within the strata.
Fossils of species that survived for a relatively short time can be used to match isolated rocks: Such index fossils must be distinctive, globally distributed, and occupy a short time range to be useful. Misleading results can occur if the index fossils are incorrectly dated.
Stratigraphy and biostratigraphy can in general provide only relative dating A was before B , which is often sufficient for studying evolution.