Ch 17 geology

Sedimentary rocks being deposited today on the east and west coasts of North America have the same

numerical age and relative age compared with the materials on which they are being deposited.

The shorter the half-life of a radiogenic element, the more useful it will be for dating

very young events

The principle of inclusions states that

a sedimentary rock must be younger than the clasts that it contains.

The longest interval of geologic time is a

eon

After three half-lives have elapsed for an element, the percentage of parent element atoms present will be

12.5%.

A nonconformity occurs when

a series of sedimentary rocks sits upon eroded igneous rocks.

If a sequence of sedimentary rocks has been folded and is now vertical

graded bedding can help determine whether some beds are older or younger than the beds next to them.

The numerical age of a sedimentary rock can be determined in the field from

graded bedding. mudcrack orientation. **none of the above** the fossils it contains.

A disconformity occurs when

there has been some uplift and erosion but no folding between deposition of rocks above and below the disconformity.

The term relative age refers to

whether a feature is older or younger than another.

If a fault offsets a sequence of sedimentary rocks it must be

younger than the rocks based on the principle of cross-cutting relationships.

A sedimentary rock contains zircon clasts that have been dated radiometrically as ranging from 1.0 billion to 250 million years old. The oldest that the rock can be is

250 million years.

The principle of superposition can be used to determine the relative ages of all except

folded sedimentary rocks.

An angular unconformity is evidence that

there is an incomplete geologic record preserved in an area.

In order for a fossil to be used as an index fossil, the species must have existed for a

very short span of geologic time and lived throughout the world.