Principle of Uniformitarianism
Dana Desonie, Ph.D.
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Printed: November 26, 2015
AUTHOR
Dana Desonie, Ph.D.
www.ck12.org
C HAPTER
Chapter 1. Principle of Uniformitarianism
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Principle of
Uniformitarianism
• Explain how scientists use knowledge of Earth in the present to understand Earth’s history.
• Summarize the principle of uniformitarianism.
What does this mean: "The present is the key to the past"?
How can this photo help you to figure out what happened in Earth’s history? You see the molten lava. You see what
the rock looks like when the lava cools. What if you see that type of rock in an outcrop? You can assume that it
formed from molten lava. This is the best tool for understanding Earth history. Earth scientists use what they know
about Earth in the present to figure out what happened in the past.
Ask a Question: Earth History
The outcrop in the Figure 1.1 is at Checkerboard Mesa in Zion National Park, Utah. It has a very interesting pattern
on it. As a geology student you may ask: how did this rock form?
If you look carefully at the rock, you will see that it’s made of sand. This rock formation is called the Navajo
sandstone. Does knowing that the rock is sandstone tell you how it formed? No, although it limits the possibilities.
The next thing to do is to make observations now and apply them to this rock that formed long ago.
Uniformitarianism
James Hutton came up with this idea in the late 1700s. The present is the key to the past. He called this the principle
of uniformitarianism. It works like this: we understand a geological process that happens now. We see the outcome
of that process, say a rock. Then we find evidence that same process happened in the past, like a similar rock. We
can assume that the process operated the same way in the past.
Let’s go back to that outcrop. What would cause sandstone to have layers that cross each other, a feature called
cross-bedding?
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FIGURE 1.1
Checkerboard Mesa in Zion National
Park, Utah.
Answer a Question: Earth History
In this photo of this sand dune in Coral Pink Sand Dunes State Park, Utah ( Figure 1.2), we see that wind can cause
cross-bedding in sand. Cross-bedding is due to changes in wind direction. There are also ripples caused by the wind
waving over the surface of the dune.
This doesn’t look exactly like the outcrop of Navajo sandstone, but if you could cut a cross-section into the face of
the dune it would look very similar.
Since we can observe wind forming sand dunes with these patterns now, we have a good explanation for how the
Navajo sandstone formed. The Navajo sandstone is a rock formed from ancient sand dunes. The rock shows that the
ancient wind direction changed from time to time.
This is just one example of how geologists use observations they make today to unravel what happened in Earth’s
past. Rocks formed from volcanoes, oceans, rivers, and many other features are deciphered by looking at the
geological work those features do today.
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Chapter 1. Principle of Uniformitarianism
FIGURE 1.2
Sand dune in Coral Pink Sand Dunes
State Park, Utah.
Summary
• You may need to apply what you know about the present to determine what happened in the past.
• The idea that the present is the key to the past was recognized by James Hutton in the late 1700s.
• If you see something forming by a process today and then find the end results of that process in the rock
record, you can assume that the the process operated the same way in the past.
Explore More
Use this resource to answer the questions that follow.
• Dinosaur Ridge –Stop One: Beach at http://www.youtube.com/watch?v=yVl0kIqzHeE (3:40)
MEDIA
Click image to the left or use the URL below.
URL: http://www.ck12.org/flx/render/embeddedobject/1637
1. How does a geologist use observations about how and where ripple marks are found to understand ripple
marks in a rock?
2. What do the colors of the rocks tell us?
3. Explain the principle of uniformitarianism.
4. Why are the principles discussed in this video important for Earth science?
Review
1. What does an Earth scientist often need to answer a question about something that happened in Earth’s distant
past?
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2. James Hutton is sometimes called the father of geology. Why does he deserve that title?
3. How can you use the principle of uniformitarianism to figure out how a lava rock formed?
References
1. Flickr:bumeister1. Checkerboard Mesa in Zion National Park, Utah . CC BY 2.0
2. Image copyright Dean Pennala, 2013. Sand dune in Coral Pink Sand Dunes State Park, Utah . Used under
license from Shutterstock.com
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