Steno's Laws and Principle of Inclusion Review

Uncover Earth's history! Learn Steno's Laws and Inclusion to date rock layers.

Younger rocks are on the top. Older rocks are on the bottom. Law of Superposition Anything cutting across a rock layer is YOUNGER. The rock had to be there first. Law of Cross Cutting Relationship rocks and minerals inside other rocks are older than the rocks they are within Principle of Inclusion sediments are laid down on flat surfaces Law of Original Horizontality Sediments are deposited in large continuous sheets in all lateral directions. Law of Lateral Continuity Age of a rock compared to another rock Relative Age In the above diagram the oldest rock layer is 1 2 3 4 In the above diagram the youngest rock layer is 1 2 3 4 Why are inclusions in rocks excellent indicators of relative age? Inclusions are usually the same age as the rock in which they are found because the inclusion and the rock that contains it must have formed at the same time. Inclusions are older than the rock in which they are found because the inclusion must have been part of some pre-existing rock, now somehow contained within a relatively new rock. Inclusions are younger than the rock in which they are found because the inclusion must form after the rock that now contains it. Inclusions are sites within a rock of missing time and were originally horizontal and cross-cutting. In the above diagram the rock layer that was formed second is 1 2 3 4