Which term describes a time gap in the geological record caused by erosion and non-deposition?

Which term describes a time gap in the geological record caused by erosion and non-deposition?

• A. Unconformity
• B. Faulting
• C. Extrusion
• D. Intrusion

Answer: (A)

In geology, a surface that marks a period with no rocks being deposited or with older rocks being worn away creates a missing chunk of time in the record. This is called an unconformity. It shows up where older rocks are separated from younger rocks by a boundary that represents the gap in time, meaning that deposition paused or erosion removed material before newer rocks formed on top. Think of it as a bookmark in Earth's history, indicating a hiatus between layers. The other terms describe different processes that affect rocks but don’t by themselves denote a time gap in the rock record. Faulting involves rocks breaking and moving along faults, extrusion refers to lava flowing onto the surface, and intrusion is magma pushing into existing rocks underground. These are tectonic or igneous processes, not necessarily indicators of a missing interval in time.

In geology, a surface that marks a period with no rocks being deposited or with older rocks being worn away creates a missing chunk of time in the record. This is called an unconformity. It shows up where older rocks are separated from younger rocks by a boundary that represents the gap in time, meaning that deposition paused or erosion removed material before newer rocks formed on top. Think of it as a bookmark in Earth's history, indicating a hiatus between layers.

The other terms describe different processes that affect rocks but don’t by themselves denote a time gap in the rock record. Faulting involves rocks breaking and moving along faults, extrusion refers to lava flowing onto the surface, and intrusion is magma pushing into existing rocks underground. These are tectonic or igneous processes, not necessarily indicators of a missing interval in time.