Dating geological specimens
The degree to which the remains are decayed when covered determines the later details of the fossil.
Some fossils consist only of skeletal remains or teeth; other fossils contain traces of skin, feathers or even soft tissues. In some cases the original remains of the organism completely dissolve or are otherwise destroyed.
The observation in the 19th century that certain fossils were associated with certain rock strata led to the recognition of a geological timescale and the relative ages of different fossils.
The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the absolute ages of rocks and the fossils they host.
There are many processes that lead to fossilization, including permineralization, casts and molds, authigenic mineralization, replacement and recrystallization, adpression, carbonization, and bioimmuration.
to dinosaurs and trees, many meters long and weighing many tons.
This process can occur in very small spaces, such as within the cell wall of a plant cell.
In some cases mineral replacement of the original shell occurs so gradually and at such fine scales that microstructural features are preserved despite the total loss of original material.
A shell is said to be recrystallized when the original skeletal compounds are still present but in a different crystal form, as from aragonite to calcite.
Radioisotope dating techniques have shown that this water is many thousands of years old.
The use of such water, which is not being recharged under the current climatic regime, is termed groundwater...
Knowing the rate of decay of one nuclear species (nuclide) into another, scientists can, in principle, use the ratios of decay products as a clock to measure the....solar system; for this reason they are often called long-lived radionuclides.