Geologic Time
Saturday, November 22, 2013
Wayne Ranney
We have now got to the end of our reasoning and have the satisfaction to find that in
nature there is wisdom, system, and consistency. In the natural history of this earth,
there is a succession of worlds and … it is in vain to look for any thing higher
[regarding] the origin of the earth. The result, therefore, is that we find no vestige of
a beginning — no prospect of an end. —James Hutton, "Theory of the Earth", 1795
Introduction
One of the things setting humans apart from other higher-level organisms is our ability to
discern time. We think about the past and ponder our future. In our minds, we have the ability to travel backwards and forwards in time. But the concept of geologic time is a recent
discovery that is often challenging to beings that live generally less than 100 years. Our ancient forbearers could not conceive of geologic time. Biblical concepts of time are limited to
about 6,000 to 10,000 years, while most people are comfortable with time increments going
back only to the time of Christ or 2,000 years ago.
Geologic time is not merely a tool for the geologist – it frames the way all of us view our
world and ourselves. When humans first discovered that the Earth was not at the center of
the solar system, or that multiple ancient landscapes existed before the modern one, it
changed forever our relationship to Earth and our very existence. In this salon we explore the
milestones that led to the concept of “deep time” and discuss its larger meaning, which can
be deeply gratifying but is unfortunately lost to most people. An awareness of the pageantry
of deep time tugs at our philosophical heartstrings and propels us into a new relationship
with Earth and for ourselves.
nau.edu/ppi
Key Milestones in the Discovery of Geologic Time

Ancestors to humans become bipedal, cooperate with one another on hunts, domesticate fire,
cook meat and ultimately evolve larger brains allowing for the development of tools, language
and civilization. We become human.

Religion develops no later than the time of the Neanderthals (100,000 years ago), invoking an
afterlife and a sense of something much bigger than us.

In classical antiquity, Aristotle noted that fossil seashells were like modern ones and thus once
living animals. He also noted that the positions of land and sea had changed over long periods of
time. The Bible attempts to reveal a long view of time since the “Creation”. In the 11th-century,
Avicenna (Persian), examined various fossils and said they were ‘petrified’ plants and animals.
A Chinese naturalist, Shen Kuo recognized the concept of 'deep time'. Leonardo da Vinci noted
that sea fossils in the mountains of Italy were the remains of ancient life.

Natural philosophers in the 17th and 18th centuries attempted to reveal how the natural world
might hold evidence for Noah’s Flood. The methods they used to reveal the secrets of Earth history were particularly satisfying (encouraging more discovery) and ultimately became the foundations for the science of geology.

Nicolas Steno formulated the “Law of Superposition” and the “Law of Original Horizontality”.
Abraham Gottlob Werner developed the first time scale with Primary, Secondary, Tertiary, and
Quaternary periods (the latter two still in use). In 1779, the Comte du Buffon estimated the Earth
was 75,000 years old.

James Hutton publishes “Theory of the Earth” in 1795, considered the first formal geology book.
William Smith makes the world’s first geologic map in 1805 with his nephew proposing later
that the Earth was 96 Ma (million years old).

1799, the first modern geologic period, the Jurassic, was named after rocks in the Jura Mountains; in 1879 the final period, Ordovician was named. In 1896 radioactivity discovered by Madame Curry; in 1907 radiometric dating was first utilized; in 1913 Sir Arthur Holmes published
“The Age of the Earth” and suggested an age of 1,960 Ma; the 4.6 Ga age for the Earth was
firmly established by about 1960. Dating methods continue to become perfected
Terms:
Ka = Kilo-annum (thousand); Ma = Mega-annum (million); Ga = Giga-annum (billion)
Book Resources:
The Seashell on the Mountaintop, by Alan Cutler, 2003, Plume, New York
The Man Who Found Time, by Jack Repcheck, 2003, Perseus Publishing, Cambridge
Descartes Bones, by Russell Shorto, 2008. Doubleday Publishing, New York
The Map That Changed The World, by Simon Winchester, 2001, Harper Collins
Web Resources:
The Geologic Time Scale: http://en.wikipedia.org/wiki/Geologic_time_scale
Understanding the concept of geologic time and some basic science can give a new perspective on climate
change and the energy future: http://theamericanscholar.org/what-the-earth-knows/ - .UozvfqW6CPV
The Historical Discovery of Deep Time: http://palaeos.com/timescale/historical/historical.html
The Radiometric Dating of Rocks: http://palaeos.com/timescale/radiometric_dating.htm