Uniformitarianism, Horizontality and Time

I briefly describe the principle of uniformitarianism, the principle of original horizontality, and the fact that younger beds overly older beds (surprise, surprise!). These concepts are key ideas for my course in Sedimentology and Stratigraphy. This video is my first and is intended as a study aid. You can also see my lecture notes at http://dawnssedstrat.blogspot.com/2011/01/lecture-1-sedimentology-and_03.html

Category:

Education

Tags:

• geology
• sedimentology
• stratigraphy
• sediment
• science

[sumnerd]

borimapa's comment about sediments deposited side-by-side is interesting. In special circumstances, older & younger sediments can be horizontally juxtaposed; a steep-sided tidal channel can be filled with younger sediments creating a horizontal juxtaposition. However, specific features indicate that this is an exception to the general principle. For example, layering will not cross the boundary, lamination at the boundary may indicate a slope, an erosional surface will be present, etc.

[borimapa]

young rocks are always on top of old rocks, only if sediments are deposited horizontally. I a situation where they are deposited side by side, this principle does not apply at all.

[sumnerd]

It does still apply in part. The bottom part of any sedimentary unit was deposited before (or simultaneously with) the upper part, consistent with the principle of younger over older for sedimentary rocks. This principle doesn't exclude rocks of different ages being next to each other horizontally.

[JohannesAarmo]

All of those principles are proven wrong in actual experiments. Not just stressing theories on youtube and against student.

[sumnerd]

I assume that by "all of those principles" you mean the ideas I discuss in the video.

These ideas are not proven wrong in experiments; experiments support them, and observations of natural processes and relationships in the rock record demonstrate that they provide a useful framework for understanding earth history. A good scientist keeps an open mind, understands her assumptions, and tests his ideas and conclusions. The ideas I discuss have withstood more than 100 years of testing.

[dieselbeetleful]

it's so weird, the concept of uniformitarianism. it kind of seems like this guy had too much time on his hands.

[deviouskrew]

thank you for the video, it was very helpfull. I am studying for a test, this should help!

[mapmanic]

sumnerd, you are performing a valuable public service by producing these videos and then patiently (and gently) correcting the misconceptions expressed in some of the posts.

I dream of a time when lectures from all our professors will be available online--they should be so now, at least for those at public universities, since the public is paying a substantial amount of the cost.

[CmanCorporations]

lol.

these seem common sense don't they?

i didn't really get uniformism, but at least for the principle of superpostiion. how can you argue that older rocks are NOT at the bottom of a sediment? doesn't that just make sense?

[sumnerd]

We date special layers. Here are 2 ways: 1) If the layers are young enough, geologists try 14C dating on plants that grew when the layer formed. 2) If volcanic ash falls from the air to form a layer, minerals that cooled during the explosion will be the same age as the layer. Geologists use radioactive decay relationships to calculate the age of these minerals & the layer.

Good geologists question the quality of dates and objectively evaluate whether they actually reflect the age of the layer.