Ineed (again! ) what does an unconformity in a sequence of rock layers reveal about geologic history?

the layers must cover hundreds of square miles.

a layer of rock might have eroded.

a rock layer must have turned upside down.

the layers must have been deposited very quickly.

b. a layer of rock might have eroded an unconformity is basically a space in the geologic record.  you cant really tell what happened there, only that a layer is no longer there for one reason or another, usually erosion.

Explanation:

(b) The rock layer might have eroded.

Explanation:

As a rock ages, it may become eroded. This can be seen in the damaged layer.

Hope this helps!