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Department
Environmental Science
Course Code
EESA06H3
Professor
Nick Eyles

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Chapter 19
Time and Geology
Introduction
Relative time unraveling the sequence in which geologic events occurred.
For example finding out that the glacial sediments found near the ground
surface are younger than the layered sedimentary rock they cover.
Radioactive isotope dating determining how many years ago rocks
formed. For example, finding out that rocks forming the North America
craton range in age between 4 billion years and 1 billion years old
What is uniformitarianism?
Until the 1800
Western culture - believed that the Earth is only a few thousand years
old
Chinese/Hindu believed the age of the Earth was beyond
comprehension (like what is determined today)
Christian formation of all rocks and other geologic events were placed
into a biblical chronology
oFossils found today were believed to be from Noahs flood
James Hutton
18th century
The father of modern geology
He realized that geologic features could be explained through present-
day processes
oSaw that our mountains are not permanent but rather are
carved into its present shape and will be eroded
oNoticed that the earth must be older than 6,000 years old for
sediments and mountains to be eroded and thicken
oWe fin no sign of a beginning no prospect for an end
Charles Lyell
Principles of geology book
Lyell referred to Huttons concept that geologic processes operating at
present are the same processes that operated in the past as the
principle of uniformitarianism.
Uniformitarianism - The present is the key to the past
James Hutton & Charles Lyell recognized that landscapes had evolved over
many millions of years by the processes that we will see operating today
www.notesolution.com
Uniformitarianism (actualism)– the same processes and natural laws that
operated in the past are those we can actually observe or infer from
observation as operating at present
Numerical age (absolute age) dating based on radioactivity allows us to
determine this, which is age given in years or some other unit of time (does
not have to be exact age ex. One and a half century ago)
Relative time geologists working in the field/laboratory and with
maps/pictures are concerned with this, which is the sequence in which events
took place, than with the number of years involved
How can the sequence of past geological events be determined?
Principles Used to Determine Relative Time
Contacts are the surfaces separating two different rock types or rocks of
different age, they can be used to determine the geologic history of an area
Formations are bodies of rock of considerable thickness with recognizable
characteristics that make each distinguishable from adjacent rock units
Stratigraphy a subdiscipline of geology that uses interrelationship
between layered rocks (mostly) or sediments to interpret the history of an
area or region.
It uses four principles to determine the geologic history of the region:
1.Original horizontality
States that beds of sediment deposited in water formed as
horizontal or nearly horizontal layers
2.Superposition
States that within a sequence of undisturbed sedimentary or
volcanic rocks the layers get younger going from bottom to top
3.Lateral continuity
States that an original sedimentary layer extends laterally until
it tapers or thins at its edge
4.Cross-cutting relationships
States that a disrupted pattern is older than the cause of
disruption. A layer cake (the pattern) has to be baked
(established) before it can be sliced (the disruption)
In order for the valley to the formed the horizontal and tilted
rocks needed to be formed first
www.notesolution.com

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Description
Chapter 19 Time and Geology Introduction Relative time unraveling the sequence in which geologic events occurred. For example finding out that the glacial sediments found near the ground surface are younger than the layered sedimentary rock they cover. Radioactive isotope dating determining how many years ago rocks formed. For example, finding out that rocks forming the North America craton range in age between 4 billion years and 1 billion years old What is uniformitarianism? Until the 1800 Western culture - believed that the Earth is only a few thousand years old ChineseHindu believed the age of the Earth was beyond comprehension (like what is determined today) Christian formation of all rocks and other geologic events were placed into a biblical chronology o Fossils found today were believed to be from Noahs flood James Hutton 18 century The father of modern geology He realized that geologic features could be explained through present- day processes o Saw that our mountains are not permanent but rather are carved into its present shape and will be eroded o Noticed that the earth must be older than 6,000 years old for sediments and mountains to be eroded and thicken o We fin no sign of a beginning no prospect for an end Charles Lyell Principles of geology book Lyell referred to Huttons concept that geologic processes operating at present are the same processes that operated in the past as the principle of uniformitarianism. Uniformitarianism - The present is the key to the past James Hutton & Charles Lyell recognized that landscapes had evolved over many millions of years by the processes that we will see operating today www.notesolution.com
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