Final answer:
Three types of clues to the relative age of rock layers are fossils, index fossils, and unconformities.
Step-by-step explanation:
Three types of clues to the relative age of rock layers are:
- Fossils: Fossils are remains or traces of ancient organisms that can be found in sedimentary rocks. By studying the fossils found in different layers of rock, scientists can determine the relative age of the rock layers. Fossils found in deeper layers are generally older than those found in higher layers.
- Index Fossils: Index fossils are fossils of organisms that lived for a relatively short period of time but had a wide geographic distribution. These fossils can be used to correlate and date rock layers. For example, if an index fossil is found in a particular layer, it can be inferred that the rock layer is of a similar age as other rock layers that also contain the same index fossil.
- Unconformities: Unconformities are gaps in the rock record that occur when there is a period of erosion or non-deposition. When rock layers are eroded away or not deposited for a time, there is a break in the sequence of rock layers. Unconformities can help determine the relative age of rock layers by identifying periods of missing time or erosion.