1.2. Geological Time
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Geology
Date
Feb 20, 2024
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1/28/24, 12:24 AM
1.2. Geological Time: EOSC 326 99C 2023W2 Earth and Life Through Time
https://canvas.ubc.ca/courses/130823/pages/1-dot-2-geological-time?module_item_id=6194667
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1.2. Geological Time
Age of the Earth
In the western tradition, one of the earliest and most influential figures in the interpretation of
geological time was James Ussher (1581 - 1665), Archbishop of Armagh. An important
historical figure in his own right, Ussher also published a chronology of Earth's history using all
dates mentioned in the Bible to establish a timeline. Using this technique, he established the
first day of creation to be October 22, 4004 BC. This date would make the Earth a little over
6,000 years old!
Figure - James Ussher (1581 - 1665), Archbishop of Armagh.
Image from Wikipedia
(http://en.wikipedia.org/) .
As science continued to develop during the 1700s, people started to become dissatisfied with
Ussher's estimated age for the planet. One such scientist and notable natural historian was
George Louis De Buffon (1707 - 1788). Believing the Earth to have been initially as a hot
molten mass, Buffon heated iron spheres (which he thought was a reasonable model for the
structure of the planet) and calculated the time they took to cool. Using this method Buffon
believed the Earth to be around 75,000 years old.
1/28/24, 12:24 AM
1.2. Geological Time: EOSC 326 99C 2023W2 Earth and Life Through Time
https://canvas.ubc.ca/courses/130823/pages/1-dot-2-geological-time?module_item_id=6194667
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Figure - George Louis De Buffon (1707 - 1788).
Image from Wikipedia
(http://en.wikipedia.org/) .
Irish Geologist John Joly published a paper in 1899 in which he estimated the Earth's oceans
(which he believed to be the same age as the planet) to be about 90 million years old. He
calculated this by estimating how long it would take for the oceans to reach their current salinity
(from an original fresh water state) as salt is added via the erosion of minerals in rocks. (Today
we understand that the Earth's oceans have not been getting increasingly salty with time. As
such, present day salinity levels cannot be used as a gauge to estimate the passage of
geological time.)
Figure - Ocean water. Photo by S. Sutherland.
1/28/24, 12:24 AM
1.2. Geological Time: EOSC 326 99C 2023W2 Earth and Life Through Time
https://canvas.ubc.ca/courses/130823/pages/1-dot-2-geological-time?module_item_id=6194667
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Later in his career Joly was to work with Ernest Rutherford using radioactive decay in minerals
to estimate the age of rocks. This technique provides us with the current age of the Earth at
4.6 Ga
(Giga-anum: billions of years).
Deep Time
4.6 Ga is a vast amount of time, especially when the oldest recorded human being
(http://www.nytimes.com/1997/08/05/world/jeanne-calment-world-s-elder-dies-at-122.html) was
only 122 years old when she died. It is this vast amount of time that the geologist and
paleontologist must consider when trying to understand the evolution of the Earth and its
biological systems. This is often referred to as the concept of deep time
.
Analogy is often used to help people grasp the vast tracts of time that have passed since our
planet formed. If you compress all of Earth's history into one year, these are some of the
significant events in our planets history:
January 1: Earth accretes out of Solar disk
February 1: Formation of oldest rock (preserved until today)
November 15: Creatures with shells first appear
December 15: Dinosaurs evolve
December 26: Dinosaurs become extinct
December 31, 23:59:18: end of last Glaciation
December 31, 23:59:46: Birth of Christ
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1/28/24, 12:24 AM
1.2. Geological Time: EOSC 326 99C 2023W2 Earth and Life Through Time
https://canvas.ubc.ca/courses/130823/pages/1-dot-2-geological-time?module_item_id=6194667
4/4
Figure - An artist's rendition of Geological Deep Time.
Image from Wikipedia
(http://en.wikipedia.org/) .