unconformity
un-con-FOR-mih-tee
A gap in the geological record — a surface between rock layers where time is missing. Below the line, one world; above it, another, separated by millions of years of erosion or non-deposition that left no trace. An unconformity is the earth's silence — the ages it chose not to record.
Etymology
English un- + conformity. The layers do not conform — the younger rock does not follow continuously from the older.
Notes
The Great Unconformity at the base of the Grand Canyon spans over a billion years.
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