Relative Age Relationships Steno’s Laws Relative Age Relationships

Nicolas Steno Born in Copenhagen The son of a goldsmith Considered by some of father of geology and stratiography

Early Questions He was brought a shark head for autopsy and noticed that the shark’s teeth resembled the “stony tongue” rocks he had found embedded in other rocks. This caused him to be curious about the solids within solids he had found.

Findings Steno was not only interested in “fossils as we would define them today, but minerals, crystals, incrustations, veins, and even entire rock layers or strata.” He assumed that “all rocks and minerals had once been fluid, Steno reasoned that rock strata and similar deposits were formed when particles in a fluid such as water fell to the bottom.”

Relative Age To Steno, the deeper the rock layer, the older its origin and vise versa. If fossils were found in that layer it presented a type of timeline of the organisms that existed at that time.

Law of Superposition Basically stated: the oldest layer will lie below or underneath the youngest.

Law of Original Horizontality Sedimentary rocks are originally deposited lying flat Later undergo tilting or folding

Law of Cross Cutting If a rock layer is cut by a fault or igneous intrusion, the rock that is cut must be older than the layer that cuts it. Layers are older than the rock that cuts them.

Law of Lateral Continutity Rock layers will extend outwards until they grade into those produced in adjacent environments.

Conclusions All that is needed to find the relative age of a rock layer is its original position. To know the original position you must first assume how the layer was folded, in what directions, and any other factors that can be seen.