Question

Within a sequence of undisturbed sedimentary rock layers, where would the oldest layer be located?

1. on the bottom
2. on the top
3. in the middle
4. could be located anywhere in the sequence with equal probability

Answer 1

According to the principle of superposition, the oldest layer in an undisturbed sequence of sedimentary rock is found on the bottom, with younger layers stacked above it.

Step-by-step explanation:

The oldest layer in a sequence of sedimentary rock layers is typically located on the bottom, according to the principle of superposition. This principle posits that in undeformed stratigraphic sequences, the oldest strata will be at the base of the sequence, with younger layers successively above them.

The principle of original horizontality further supports this, indicating that sediments are originally deposited in horizontal layers, and significant tilting or disturbance occurs after deposition. When studying rock formations and fossils, geologists rely on these principles, along with others such as lateral continuity and correlation based on fossil content, to understand the relative age of rock layers and any geological events that may have altered their original sequence, such as folding, tilting, or the presence of unconformities.