Start Relative age dating and radiometric age dating

Relative age dating and radiometric age dating

U-235 is the parent isotope of Pb-207, which is the daughter isotope.

Some elements have forms (called isotopes) with unstable atomic nuclei that have a tendency to change, or decay.

It wasn't until well into the 20th century that enough information had accumulated about the rate of radioactive decay that the age of rocks and fossils in number of years could be determined through radiometric age dating.

This activity on determining age of rocks and fossils is intended for 8th or 9th grade students.

The teacher should tell the students that there are two basic principles used by geologists to determine the sequence of ages of rocks.

They are: Principle of superposition: Younger sedimentary rocks are deposited on top of older sedimentary rocks.

Diagenetic xenotime occurs in a wide variety of rock types, including conglomerate, sandstone, siltstone, shale, phosphorite and volcaniclastic rocks, varying from early Archaean to Mesozoic in age.

The formation of diagenetic xenotime is principally related to redox cycling of Fe-oxyhydroxides and microbial decomposition of organic matter, leading to elevated concentrations of dissolved phosphate and rare earth elements (REE) in sediment pore-waters.

Return to top Each team of 3 to 5 students should discuss together how to determine the relative age of each of the rock units in the block diagram (Figure 1).