Are only sedimentary rocks used for relative age determination? Why?

Question

Nova Anderson · Accepted Answer

relative age determination is based on fossils and only sedimentary rocks contain fossils.

Based on Darwinian evolution and index fossils, the relative age is calculated: the simpler the fossil, the older it is assumed to be; if a complex fossil is discovered in a strata below one that contains an index fossil that is assumed to be older based on Darwinian evolution, the lower strata are classified as younger. Because fossils can only be found in sedimentary strata, only sedimentary strata can be used to calculate relative ages.

Mason Allen · Answer

undefined No, sedimentary rocks are not the only rocks used for relative age determination. While sedimentary rocks are commonly used because they often contain fossils that can be used to correlate rock layers, igneous and metamorphic rocks can also be used. Igneous rocks can be dated using radiometric methods, providing absolute ages that can be used to establish relative ages of surrounding rocks. Metamorphic rocks can be correlated based on their mineral composition and the sequence of metamorphic events they have undergone. Therefore, all three types of rocks can be utilized for relative age determination, depending on the geological context and available dating methods.