What is the laws of...?

Question

Can someone explain the Laws of Superposition and Cross-cutting?
I don't understand it.

Answer 1

The Law of Superposition states that all sediments are deposited in a horizontal fashion where the oldest sediments will be the bottom layer and the youngest sediments will be the top later of a rock formation.

EXAMPLE:

Think about pouring candy into a jar. One day, you pour a bag of M & Ms into a jar. Notice that they spread out at the bottom of the jar so that they are a horizontal layer (none of the candies decided to stack on top of one another and make a tower out of themselves). The next day, you come back to the jar. The M & Ms are exactly the same as you left them the day before. You then pour a bag of Skittles in the jar the same as you had with the M & Ms. They also make a horizontal layer in the jar, but instead of being at the bottom of the jar, they lay on top of the M & M layer. If you don't disturb the jar, you know that the bottom horizontal layer of M & Ms is older than the layer of Skittles.


The Principle of Cross-Cutting Relationships states that any igneous intrusion is always younger than the rock it cuts across.

EXAMPLE:

Imagine you have a loaf of bread. You take a can of Reddy Whip whip cream and put the whip cream's "nozzle" into the bread and fill the inside of the bread with whip cream. The flow of whip cream represents an igneous intrusion like a sill or a dike. The bread, which represents the original rock, was obviously sitting on the table before the whip cream even came into the picture. Thus, the original rock (bread) is older than the igneous intrusion (whip cream).

I hope this helps!

Answer 2

Superposition is about the layering of rocks- what's on the bottom had to come first, otherwise it wouldn't have been there for what came next to lay on top of it. The oldest stuff is on the bottom, the youngest is on the top.

There many ways that this can be wrong though- if there was plate movement then stuff can get folded, stretched, smooshed and flipped, occasionally putting the oldest on top!

Cross-Cutting...I don't remember.