Some of these microscopic organisms had hard parts, such as exoskeletons or outer shells, making them better candidates for preservation. Relative Age - if two rock units are equivalent they must have the same age relative to rocks that occur below and above. Next time you find a cliff or road cutting with lots of rock strata, try working out the age order using some simple principles:. Three kinds of clues help geologists match rock layers across great distances. Yes No. If two rock units both contain the same type of index fossil, their age is probably very similar.
However, if the bone is 70, years or older the amount of 14 C left in the bone will be too small to measure accurately.
Dating Rocks and Fossils Using Geologic Methods
Information such as index fossils or radiometric dates can be used to correlate a particular paleomagnetic reversal to a known reversal in the GPTS. So the fault must be the youngest formation that is seen. Geologists can measure the paleomagnetism of rocks at a site to reveal its record of ancient magnetic reversals. The principle of cross-cutting relationships states that a fault or intrusion is younger than the rocks that it cuts through. According to uniformitarianism, the same processes we see around us today operated in the past as well. John Wiley and Sons