WednesdayJanuary 4, 2012

(A Brief History of Geology; Relative

Dating)

The Launch PadWednesday, 1/4/12

What is “geology?”Geology is the study of the Earth, the materials of which

it is made, the structure of those materials, and the processes acting upon them.

It includes the study of organisms that have inhabited our planet.

An important part of geology is the study of how Earth’s materials, structures, processes and organisms have

changed over time.

http://geology.com/articles/what-is-geology.shtml

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Geology

A Brief History of GeologyDuring the seventeenth and

eighteenth centuries, the doctrine of catastrophism

strongly influenced people’s thinking about Earth.

Catastrophists believed that Earth’s landscapes had been developed primarily by great

catastrophes. James Ussher, in the mid-1600s, concluded that the

Earth was only a few thousand years old, having been created

in 4004 B.C.

A Brief History of Geology

Modern geology began in the late 1700s, when

James Hutton, a Scottish physician, published his

Theory of the Earth.

Hutton put forth a fundamental principle

that is a pillar of geology today: uniformitarianism.

A Brief History of GeologyThis principle simply states that the

physical, chemical, and biological laws that operate today have also

operated in the geologic past.

This means that the forces and processed that we observe

presently shaping our planet have been at work for a very long time..

This idea is commonly expressed as “The present is the key to the

past.”

Determining Age• How old someone or something is can be thought of

in two different ways: relatively or numerically.• For instance, consider these two scenarios:

– Frank is older than John, and John is older than Mary.– Frank is 18 years old, John is 16, and Mary is 10.

• The first statement is relative; it lists the order of the ages, but doesn’t provide actual numerical information.

• The second statement is numerical, as it gives the actual ages of the three.

• Geologists use both relative and numerical dating when accessing the age of rocks and formations.

Relative Dating Relative dating means

placing rocks in their proper sequence of formation.

This technique cannot tell us how long ago something took place, only that events

took place one after the other.

Again this is not a numerical dating procedure!

Relative Dating Principles and rules of relative dating:

The Law of Superposition states that in an undeformed sequence of sedimentary

rocks, each bed is older than the one above it and younger than the one below.

In other words, the oldest rocks are on the bottom and the youngest on the top.

Superposition is Well Illustrated in the Grand Canyon

Figure 11.3