principle of uniformitarianism

answer a question earth history

In the photo of the Mesquite sand dune in Death Valley National Park, California (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. 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 in which 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 Earths past. Rocks formed from volcanoes, oceans, rivers, and many other features are deciphered by looking at the geological work those features do today. Click image to the left or use the URL below. URL:

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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 is that if we can understand a geological process now and we find evidence of that same Checkerboard Mesa in Zion National Park, Utah. process in the past, then we can assume that the process operated the same way in the past. Hutton speculated that it has taken millions of years to shape the planet, and it is continuing to be changed. He said that there are slow, natural processes that changed, and continue to change, the planets landscape. For example, given enough time, a stream could erode a valley, or sediment could accumulate and form a new landform. Lets 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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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 poke at the rock and analyze its chemistry you will see that its made of sand. In fact, the rock formation is called the Navajo sandstone. But knowing that the rock is sandstone doesnt tell you how it formed. It would be hard to design an experiment to show how this rock formed. But we can make observations now and apply them to this rock that formed long ago.

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questions

the principle of uniformitarianism states that processes operate

a) in an unknowable manner.

b) randomly; past processes may or may not be similar to present processes.

c) differently in at present than they did in the past.

-->  d) the same way at present as they did in the past.

the idea of uniformitarianism was recognized by

a) harry hess

b) alfred wegener

-->  c) james hutton

d) jacques cousteau

a rock that is made of sand of roughly the same size probably formed in

-->  a) a sand dune

b) a deep sea environment.

c) a coral reef environment.

d) an ancient river.

geologists can identify that wind changed direction in ancient sandstone from

a) ripple marks.

b) very fine layering.

-->  c) cross bedding.

d) devils holes.

ripple marks are caused by sand slumping down a dune face.

a) true

-->  b) false

without the principle of uniformitarianism geologists could not understand earth history.

-->  a) true

b) false

rocks can form in or on

a) volcanoes

b) oceans

c) rivers

-->  d) all of the above

navajo sandstone formed from volcanic eruptions.

a) true

-->  b) false

if cross-bedded sandstone forms in dunes today, it probably formed in dunes in the ancient past.

-->  a) true

b) false

the idea that the present is the key to the past is called the principle of geology.

a) true

-->  b) false

diagram questions

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