I have folks in this video I'm gonna summarize on a simple principle called the lost superposition which simply states that the layers on the bottom the rock layers on the bottom are older than the rock layers deposited on the top this slide here summarizes on them exactly what I need you to know so if you'd like to pause it and review it please do so here are some key vocabulary terms that I'm going to be using during this presentation so if you'd like to pause it and review it and summarize please do so the main idea of the lost superposition is simply that the layers on the bottom are deposited long ago and layers of sediment on top are younger and what this allows us to do is determine the relative age or the approximate age of fossils and rock layers which can be extremely useful in order to date how old a fossil or rock layer is the relative age doesn't tell us the exact age of an object such as a rock layer fossil but it does tell us a lot about you know its approximate age which is really useful there's two ways we can determine the relative age of something one is the order of the rock layers or the loss superposition and another way is the use of index fossils which I'll outline in another video so in this video I will be summarizing how we use the order of rock layers or the loss superposition to determine the relative age of rock layers of fossils so this picture here I included um because it is a real-world example of how the lost superposition applies in this case you might infer or assume that the clothes and the objects on the top were used more recently and put on top and the stuff on the bottom was probably used or worn you know much later so you know the clothes and the food that might be laying on top was probably you can infer use more recently than than the items on the bottom so it's just you know the law superposition not you know just apply to you know rock layers and fossils it's also used in forensic science and you know some some common-sense examples but when it comes to rock layers the order of the rock layers is extremely useful in determining the age of fossils and rock layers and tells us a lot about Earth's history so you know the important part of this principle is really knowing that you know this layer was deposited you know first and then younger layers are deposited on top of it so the deeper we dig the further back in time we do see and this picture here is just a really simplified version of what we see in the fossil record according to the law superposition is you know in the in Earth's distant past we see more marine or ocean sea like creatures and then you know in the middle we see more reptilian like dominant creatures and then in more recent history we see you know more mammal dominant species of organisms and those rock layers so the law of superposition states that each rock layer is older than the one above it so the approximate or relative age of the rock or fossil in the rock or fossil is older if it's further down the rock layers so that's a really kind of over complicated thing compared to just saying you know the deeper you dig with further back in time you see so this cartoon summarizes it really well I think so the lot superposition states that each rock layers older than the one above it so this one would be considered the oldest and this layer here would be considered the youngest and this picture here is depicting how that process might occur this right here staged step number one would be you know in Earth's distant past you know and then sediments were deposited and this organism was fossilized and then there was a time where reptile reptilian creatures were more dominant and then they were sediments were deposited on top of that fossil and then in more recent time we see more mammal-like organisms so here's a more realistic picture of how the lost superposition could be useful here is a picture of the Grand Canyon you can see that the layers down here were deposited first and then layers were deposited on top of it over time and here they actually included some geologic you know time periods here that were part of the Paleozoic era so this this would be hundreds of millions of years of deposition and various layers here so what's interesting is that when we find fossils in the lower layer we see you know different environments and different organisms and different adaptations and then organisms and more recent layers you know have similarities and differences but what the lost superposition does is it tells us you know the approximate age of these layers here in comparison to you know layers that would be older down here so according to the lost superposition layer a would be the youngest and layer D would be you know older this picture here shows some people that are visiting the Grand Canyon you know I wish it was me unfortunately I had an opportunity to go there but I'd love to but I wanted to show you you know a more realistic version of the lost superposition you know these layers here were deposited more recently and the layers deep down here were deposited you know millions hundreds of millions of years before and it's almost like a storybook of Earth's history you know the fossils that we uncover in these different layers tell us a lot about Earth's past so at this point I would hope that you'd be able to tell me that layer one would be you know the youngest and you know layer four would be considered older according to the lost superposition you know these layers were deposited first and then sediments and sedimentary layers were deposited on top of it so at this point I would like to get you familiar with you know some diagrams like this you know diagram azor you know real simple you know example of the lawsuit position you got layer here on top would be considered the youngest it was deposited more recently and then layer G down here would be considered the oldest because it was deposited you know first and all these layers are on top of it diagram B is demonstrating that you know natural forces haven't rode and weathered some of these layers away this would be similar to the Grand Canyon and but the law of superposition still in effect you have layer a here is on top and you know layer G here on the bottom so that would make layer G older according to the loss superposition diagram see here is trying to represent it a little bit more realistic in nature because in reality it's it's not always common that layers are in perfect you know horizontal layers like this there are geologic processes that would cause layers to be pushed and moved whether it's tectonic forces or you know other things that would cause layers to shift and move but scientists are still clever and they understand those processes and can still use the lost superposition to relatively date rock layers so I still know that rock layer a even though it's moved as younger and rock date a rock d here is is the oldest even though it is also moved then layer D here has an important element that I want to get you familiar with is something called an intrusion so sometimes magma will actually you know lose up into sedimentary rock layers and I know this is younger simply because it's on top of these other rock layers even this one right here you see that a little bit there tells me that this intrusion is even younger than this layer here because it's on top and you know as you go down new rock layers get older and older and older so I want you to get familiar with these kind of diagrams this image here is very similar but it has another element that I want to get you familiar with let's just start simply here we got this rock layer here is the oldest because it's on the bottom Rock layer B is on top and then rock layers on top of B but what's interesting is you have this intrusion D which is on top of C B this intrusion letter D is also on top of layer a so that makes D younger what's also interesting is you have this you know fault line here that has occurred after this intrusion even occurred so you know rocked layer D would be the youngest rock layer however this earthquake or this fault and this slip occurred after this intrusion was created and I know that simply because layer D is on top of everything but the fault line cut or cracked this intrusion so again this is all based on the loss superposition so what loss superposition does is that allows us to relatively date or determine the approximate age of rock layers and fossils which is extremely useful however this can only be done if rock layers were preserved in their original sequence even though that's not completely true scientists are pretty clever and they can you know understand those forces and still make some you know great inferences about the relative age of rock layers and fossils on the lost superposition is generally for undisturbed layers so in conclusion we can determine the approximate age or the relative age of rock and rock layers and fossils in those rock layers using the lost superposition the lost superposition states that horizontal layers in sedimentary rock each layers older than the layer above it and younger than the layer below it so I know this layer is the oldest and then these layers were deposited on top of it and are more recent and younger so the deeper we dig the further back in time we do see I hope this lesson was helpful thank you