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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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Looking Ahead: 2012 Pivotal for Private Spaceflight
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