1. Rock layer A is the oldest. I know this because in undisturbed sedimentary rock layers, the oldest layers are at the bottom and each layer above is progressively younger (law of superposition).
2. Rock layer G is the youngest. I know this because it is at the top of the sequence, meaning it was deposited last according to the law of superposition.
3. Fossil C appears to have been on Earth for the longest amount of time. I think this because it is found in the most rock layers (A through E), indicating it existed across a long span of geological time.
4. Fossil G appears to have been on Earth for the shortest amount of time. I think this because it is only found in one rock layer (G), suggesting it existed for a brief period before going extinct.
5. When mass extinctions occur, many species disappear from the fossil record at the same time. Paleontologists look for these sudden gaps or changes in fossil assemblages across rock layers to identify when major extinction events happened.
Parent Tip: Review the logic above to help your child master the concept of rock layers worksheet.
