Earth’s History

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? All sediment begin somewhere else from where we usually find it Erosion = Eraser Deposition = Deposits = Writing History Igneous Intrusion = Writing Eroded sediments end Up somewhere else Deposited in layers

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

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

6. More examples of strata: Colorful strata near Capitol Reef National Park Can you see the fold? You can see that there are many different layers in this picture Sandstone with folded layers made of the exact same material 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): Mountain / Erosion Body of Water squeezing 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 The youngest (age) layer is on top! • 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

10. How to tell the age of rock:Relative Dating A) Comparing Strata Locations B) Index fossils 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! *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? The layers of strata are numbered along this side Find the layer with fossils that only appears once The types of fossils Are indicated here 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!

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

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: You can see the sandstone layers That were already present (old) This diagonal layer of volcanic rock cut it’s way through As magma after the sandstone was already there (young).

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

18. 15 don’t forget the tree! 14 Imperfections in the Strata 13 Q: Can you follow the order? There are 15 events/features Try to predict which layer is Next in the sequence before You click the button! Sometimes the strata is difficult to read! 10 9 7 2 Tilting=6 5 3 12? Hard to be sure… 11 4 1 8