1. Earth’s History But…there is no book! Oh…rats…

2. Why do we want to know Earth’s History? Catastrophic Events –If it has happened before, can it happen again? Environmental/Climate Changes –Global Warming? Earthquake activity –Where are the active earthquake areas? Building Project Safety –Where can we build our homes without them being destroyed? General Curiosity ***All this to help us understand how our planet got the way it is, and where it might be headed. So that we can be prepared…

3. How does Earth “write” its history? Erosion = Eraser Deposition = Deposits = Writing History Igneous Intrusion = Writing All sediment begin somewhere else from where we usually find it Eroded sediments end Up somewhere else Deposited in layers

4. Q: How do we see Earth’s history? A: Strata Stacked layers of rock and soil. Each layer is made of slightly different stuff which make them look just a bit different: There are at least three different layers in this picture: Normally, the layers are found flat And horizontal Like these But sometimes they can be tilted like these or even have their order totally mixed up as we will see! They go like this Main Concept: We can use layers of sediment to determine what the area used to be like and even figure out what has happened in the area over periods of time.

5. Horizontal Layers in a Depositional Environment Body of Water Sedimentary Rock Layers Layers of Sediment are deposited one upon the other. Clearly The layers on the bottom were deposited first.

6. More examples of strata: Sandstone with folded layers made of the exact same material Colorful strata near Capitol Reef National Park You can see that there are many different layers in this picture Can you see the fold? Originally these layers were flat and horizontal but now they Are folded and tilted…but they did start out flat

7. Horizontal Layers can get squished (they won’t look horizontal anymore): Body of Water Mountain / Erosion squeezing

8. You can see the folds caused by tectonic forces squeezing the layers of strata Strata is often messed up some and can be a bit hard to “read”

9. Q: How to tell the age of rock: A: Superposition Means: one thing placed upon another Geologic Example: Layers of rock stacked by Deposition. The cooled lava has formed a new rock layer on top of the sandstone that was already there The youngest (age) layer is on top!

10. How to tell the age of rock: Relative Dating This is not an exact method. It does not give an exact year! *Used to find the age of a fossil or rock compared to others! A) Comparing Strata LocationsB) Index fossils *If a particular species lived only in a certain time period then you know that whatever layer you find its fossil, that layer is the same age as the fossil

11. Notice that what you see on one side of the stream, you also see on the other side of the stream. Comparing strata locations: We figure that even though they are not connected anymore, the layers on either side of the river are the same! The layers used to be connected, but the river has cut them in half! But we still understand that the layers are the same age!

12. Originally the layers continued all the way through: If you find one layer in one place and you find the same layer on the other side of the river – it’s probably gonna be the same layer of sediments. The layers were deposited In a shallow sea, but the sea Dried up and a river cut part Of the layers away River

13. Index Fossils Each fossil shown here is only found in the particular age that is shown: We know how long ago these time periods are: If you find one of these fossils in a layer of strata, you know when it lived and how old that layer of strata is! Any layer of strata we find this particular fossil in we know must have been deposited in the Jurassic Period which was years ago…

14. Where is the index fossil? Find the layer with fossils that only appears once Here it is!!! ***The yellow spiral shell fossil only appears in this single layer. If we know when this critter lived, when know exactly when this layer was deposited! And we can make estimates of when the layers above and below were deposited as well! The layers of strata are numbered along this side The types of fossils Are indicated here

15. Can you match up the layers? The soil and rock between these 3 locations has been eroded away. Fill in the empty spaces: There are two index fossils indicated here as well. They help Us match the layers together! Notice that layer D is totally missing in location 2 Something has caused this layer to disappear between location 2 and 4 Why are layers sometimes “messed up”:

16. Why are layers sometimes “messed up”: Volcanic “Intrusion” Example: “Intrusion” means that magma has cut it’s way through other layers that were already there! Now it has become igneous rock: This diagonal layer of volcanic rock cut it’s way through As magma after the sandstone was already there (young). You can see the sandstone layers That were already present (old)

17. Why are layers sometimes “messed up”: Faulting and Folding Earthquake events can mix layers up and put them totally out of order. Top Bottom The fold has caused what should be the bottom To become the top The layers are getting separated Fault

18. Imperfections in the Strata Sometimes the strata is difficult to read! Q: Can you follow the order? There are 15 events/features There are 15 events/features Try to predict which layer is Next in the sequence before You click the button! 1 2 3 4 5 Tilting=6 7 8 9 10 1112? Hard to be sure… 13 1415 don’t forget the tree!