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.
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.
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.
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.
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.
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?
As an engineer, I design hydraulic stilling devices and systems. The major technique, which mirrors the natural, is to create turbulence.
The turbulence of any stream of even minor capacity (say, 100 CFS) will turn over rocks and churn them. A major rain event (eg 50 year storm) will move everything, mix it up, and dump it.
I agree with mrmacmasonry, below. Assuming gradual deposit -and horizontal- contradicts the actual field situation. This is not "a trivial assumption."
Rocks are churned during erosion. In deposited layers that process has stopped; the rocks no longer move. Rocks always land on rocks that stopped moving at an earlier time. Thus, the rocks on top were deposited after the rocks underneath. A single layer can be deposited almost at once, but overlying layers must be deposited on an underlying, older layer.
Layers are GENERALLY close to horizontal; this approximation is important to evaluate when looking at rocks in the field.
The rocks churned up and carried downstream are from "old" layers as well as new. The new deposit comprises a mix of "old" and "new". However, this process has been repeating for thousands of years. At a minimum, there should be a statistical model to represent the composition of each layer. And this will be true only if the mixing is imperfect... AND new rocks are somehow being produced.
The ages of individual rocks are older than the age of the layer they are deposited in. The rocks in rivers come from pre-existing rocks, For example rivers flowing off Mt. Shasta (a volcano) have rocks and sand that formed when the volcano erupted. If you watch a layer being deposited, the layer has an age of 0 years, but the individual rocks will have many different ages, all older than 0 years. The age of a layer is the age when the layer formed, not the age of the rocks within it.
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.
That's a good starting point, but it sort of lies by omitting the mechanism by which multiple simultaneous layers are laid down by moving water. So, parts of lower layers further downstream are younger than layers on top of them. This is where catastrophism trumps gradualism.
I disagree. Sediment is always deposited on a pre-existing surface, with older under younger sediments when deposited.
Also, both catastropic and gradual events deposit sediment and are preserved in the rock record. The key is to recognize both types of processes and interpret earth history from that record.
Wow great Video Its really amazing to see some videos from which you can get some knowledge....Well being a Geology student i found here very intresting stuff.....
Uniformitarianism is basically dead. Slow processes can't completely explain what we see in the geologic record. What we really have are long periods of slight change (uniformitarianism) followed by sudden extreme catastrophe. Then long periods of slight change again.
It's a mix. With more changes being made by the catastrophes (floods, volcanoes, etc) than by the slow accumulation of sediments.
You are right; catastrophic events have a huge influence. However, the way I use the idea of uniformitarianism encompasses these events: Similar processes in the past and present produce similar results. For example, a meteorite impact today would produce the same structures that impacts in the past produced. This connection between uniform processes producing uniform results is the key to interpreting earth history. "Uniformitarianism" used this way is a very powerful concept.
You are correct, ookiewonderslug, the entire focus of recent NPDES environmental legislation addresses the fact that 50-year and 100-year storms change the banks, flowline and course of streams and rivers. Limiting the capacity of these events is the goal of new law. These storms erode the riverbottom, the banks and even radii of turns. Everything is mixed and deposited downstream.
it's so weird, the concept of uniformitarianism. it kind of seems like this guy had too much time on his hands.
dieselbeetleful 3 months ago
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.
sumnerd 2 years ago
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.
borimapa 2 years ago
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.
sumnerd 2 years ago
thank you for the video, it was very helpfull. I am studying for a test, this should help!
deviouskrew 2 years ago
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.
mapmanic 3 years ago 2
All of those principles are proven wrong in actual experiments. Not just stressing theories on youtube and against student.
JohannesAarmo 3 years ago
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.
sumnerd 3 years ago
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?
CmanCorporations 3 years ago
As an engineer, I design hydraulic stilling devices and systems. The major technique, which mirrors the natural, is to create turbulence.
The turbulence of any stream of even minor capacity (say, 100 CFS) will turn over rocks and churn them. A major rain event (eg 50 year storm) will move everything, mix it up, and dump it.
I agree with mrmacmasonry, below. Assuming gradual deposit -and horizontal- contradicts the actual field situation. This is not "a trivial assumption."
KnowJesusKnowPeace 4 years ago
Rocks are churned during erosion. In deposited layers that process has stopped; the rocks no longer move. Rocks always land on rocks that stopped moving at an earlier time. Thus, the rocks on top were deposited after the rocks underneath. A single layer can be deposited almost at once, but overlying layers must be deposited on an underlying, older layer.
Layers are GENERALLY close to horizontal; this approximation is important to evaluate when looking at rocks in the field.
sumnerd 4 years ago
The rocks churned up and carried downstream are from "old" layers as well as new. The new deposit comprises a mix of "old" and "new". However, this process has been repeating for thousands of years. At a minimum, there should be a statistical model to represent the composition of each layer. And this will be true only if the mixing is imperfect... AND new rocks are somehow being produced.
From where do the new rocks originate?
KnowJesusKnowPeace 4 years ago
The ages of individual rocks are older than the age of the layer they are deposited in. The rocks in rivers come from pre-existing rocks, For example rivers flowing off Mt. Shasta (a volcano) have rocks and sand that formed when the volcano erupted. If you watch a layer being deposited, the layer has an age of 0 years, but the individual rocks will have many different ages, all older than 0 years. The age of a layer is the age when the layer formed, not the age of the rocks within it.
sumnerd 4 years ago
You see, I have never before heard an intelligent explanation of this. Thank you. Can you tell me, please, how is the layer dated by archaeologists?
youmissedyourturn 4 years ago 2
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.
sumnerd 4 years ago
That's a good starting point, but it sort of lies by omitting the mechanism by which multiple simultaneous layers are laid down by moving water. So, parts of lower layers further downstream are younger than layers on top of them. This is where catastrophism trumps gradualism.
mrmacmasonry 4 years ago
I disagree. Sediment is always deposited on a pre-existing surface, with older under younger sediments when deposited.
Also, both catastropic and gradual events deposit sediment and are preserved in the rock record. The key is to recognize both types of processes and interpret earth history from that record.
sumnerd 4 years ago
Wow great Video Its really amazing to see some videos from which you can get some knowledge....Well being a Geology student i found here very intresting stuff.....
Best Wishes Dear Geology Friend:)
T care
Arshad Ali
meetgeologist 4 years ago
Uniformitarianism is basically dead. Slow processes can't completely explain what we see in the geologic record. What we really have are long periods of slight change (uniformitarianism) followed by sudden extreme catastrophe. Then long periods of slight change again.
It's a mix. With more changes being made by the catastrophes (floods, volcanoes, etc) than by the slow accumulation of sediments.
Ookiewonderslug 4 years ago
You are right; catastrophic events have a huge influence. However, the way I use the idea of uniformitarianism encompasses these events: Similar processes in the past and present produce similar results. For example, a meteorite impact today would produce the same structures that impacts in the past produced. This connection between uniform processes producing uniform results is the key to interpreting earth history. "Uniformitarianism" used this way is a very powerful concept.
sumnerd 4 years ago
You are correct, ookiewonderslug, the entire focus of recent NPDES environmental legislation addresses the fact that 50-year and 100-year storms change the banks, flowline and course of streams and rivers. Limiting the capacity of these events is the goal of new law. These storms erode the riverbottom, the banks and even radii of turns. Everything is mixed and deposited downstream.
KnowJesusKnowPeace 4 years ago
good class
gatoxxxx 5 years ago