Chapter 8Chapter 8

itarianism

A principle that geologic processes that occurred in the past can be explained by current geologic processes. Volcanism and Erosion

Uniformp.185

Relative Age

The age of an object in relation to the age of other objects

p.186

The law that a sedimentary rock layer is

older than the layers above it and younger than the layers below it if the layers are not disturbed.

Law of Superpositionp.187

A break in the geologic record created

when rock layers are eroded or when sediment is not deposited for a long period of time.

Un ities p.189conform

Absolute Age

The numeric age of an object or event, often stated in years before the present.

Using a process like “radiometric dating” or “carbon dating”

Rates of Deposition

In general, about 30 cm of sedimentary rock are deposited over a period of 1,000 years.

However, a flood can deposit many meters of sediment in just one day.

Radiometric Dating

A method of determining the absolute age of an object by comparing the relative percentages of a radioactive (parent) and a stable (daughter) isotope.

Half-Life: the time required for half of a sample of a radioactive isotope to break down.

Carbon-14 Dating

Plants absorb Carbon during Photosynthesis

Scientists compare the carbon isotopes 12C and 14C (radioactive)

This can be used to determine the ages of wood, bones, shells and other organic remains that are less than 7,000 years old.

Pa

leonto

log

y The scientific study of fossils.

Trace Fossils

Fossilized evidence of past movement of an animal such as tracks, footprints, borings and borrows.

Index Fossils

A fossil that is used to establish the age of rock layers because it is: Distinct – features different from other

fossils Abundant – occurs in fairly large numbers Widespread – present in scattered rocks Existed only for a short span of

geologic time