Which of the following methods tells you which layer of rock is oldest but does not tell you exactly how old

The method that tells you which layer is the oldest is using relative age, with this you can analyze the rock and know that they deepest one is the oldest. This answer does not have the actual method name due to the fact i cannot remember.

lizards have adapted to life in the desert. some desert lizards have toes with spiny scales to them run across the sand without sinking. some use the sand to hide from predators, or to search for small animals that they prey upon.