Relative Dating (Steno's Laws):

    Long before geologists tried to quantify the age of the Earth they developed techniques to determine which geologic events preceded another, what are termed "relative age” relationships.  These techniques were first articulated by Nicolas Steno, a Dane living in the Medici court of Italy in the 17th C.  His four observations on relative age relationships have been coined “Steno’s Laws” and are fundamental to the study of rock strata, or stratigraphy. 

1.    Law of Superposition In a sequence of rock strata, the oldest layer will lie below or underneath the youngest. Click on photo to enlarge:	2.    Law of Original Horizontality Layers of sediment, such as you would have in the bottom of a lake, or the ocean, are deposited by gravity into flat layers. Click on photo to enlarge:
3.    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. Click on photo to enlarge:	4.    Law of Lateral Continuity Rock layers will extend outwards until the environment that produced them changes. Click on photo to enlarge:

Last modified October 02 2008 03:06 PM