Geologic assessment of active tectonism depends on two key measures: the age and the amount of deformation of a given stratigraphic unit.
The amount of deformation can normally be measured with greater accuracy than the age.
The resulting fluor-apatite is more stable than the original form, thus the fluoride content of a bone will increase over time if it is exposed to a solution containing fluoride ions.
This chapter is an introduction to rocks and minerals, and the rock cycle.
Basic chemistry is important to all sciences, especially geology!
Over time, buried bones pick up fluoride ions from soil moisture or exposure to groundwater.
Older specimens have higher fluoride contents than younger ones when burial conditions are identical.
In fact, until the eighteenth century, it was commonly believed that the Earth was no older than a few thousand, or at most, million, years old.
Scientific detective work and modern radiometric technology have only recently unlocked the clues that reveal the ancient age of our planet.
They had no way of knowing the ages of individual rock layers in years (radiometric dates), but they could often tell the correct sequence of their formation by using relative dating principles and fossils.
Geologists studied the rates of processes they could observe first hand, such as filling of lakes and ponds by sediment, to estimate the time it took to deposit sedimentary rock layers.
Everything around us is made of chemical compounds that have testable and identifying characteristics, allowing them to be classified, and their age determined.