The Law of Superposition states what about rock layers in an undisturbed sequence?

• A. The oldest layers are at the bottom and the youngest layers are at the top
• B. The youngest layers are at the bottom
• C. All layers are the same age
• D. Fossils determine the age

Answer: (A)

In an undisturbed stack of sedimentary rocks, older layers form first and sit beneath younger ones that accumulate on top. Over time, new material is deposited atop the existing sediment, so the bottom layers are the oldest and the top layers are the youngest. This principle lets geologists read the sequence like pages in a book, revealing the order of deposition.

If the sequence has been disturbed by folding, faulting, or erosion, the simple bottom-to-top age order may not apply. The other statements either reverse the expected order, claim all layers are the same age, or rely on fossils alone to determine age, which isn’t the direct assertion of this law. Fossils can help compare and correlate layers, but the core idea remains the age progression from oldest at the bottom to youngest at the top.