1. Plate Tectonics Relative Dating and Rock Layers
How can rock layers tell us about Earth’s history?

2. Earth’s History

3. 1. How old is our Universe?
13.7 billion years old

4. 2. How old is Earth?
4.6 billion years old

5. 3. Earth was once made of molten lava and magma, eventually cooling to form igneous rock

6. Weathering, Erosion, Compaction, Cementation, Heat, and Pressure eventually formed the rocks that cover our Earth’s surface.

7. 4. What we know about Earth’s history comes from studying its rocks, rock formations, rock layers, and even the rocks from outer space

8. Meteorites
5. All meteorites formed about the same time that Earth formed, so studying them helps us study Earth.
6. Meteorites have not been affected by erosion, weathering or other forces the way Earth’s rocks have.

9. Studying Earth’s Rocks

10. Rock Layers Which book was placed here first? The bottom one!
7. When rocks form, the oldest ones are usually found beneath younger rocks
Sedimentary rock formation

11. Can you tell which color was put in the bottle first?

13. Fossils 8. Most fossils are found in Sedimentary rock layers 9. Why?
Heat, pressure, and melting would probably destroy fossils during the formation of Igneous and Metamorphic rocks

14. 10. Sedimentary rocks, and the fossils they trap, are often found in layers, oldest rocks are found on the bottom.

15. 11. Digging through the layers of rocks, helps us understand more about the history of Earth.

16. 12. The Grand Canyon (Arizona) was carved by the Colorado river, exposing millions of years worth of rock layers.

18. 13. Sometimes, the rock layers aren’t always horizontal…

22. 14. And sometimes ocean fossils are found high in the mountains…
Why?

23. And the layers get pushed around.
15. Turns out, our Earth’s surface is constantly shifting, changing, and eroding.
And the layers get pushed around.

24. I wonder what’s inside Earth?
16. Only in the last 200 years, have we begun to understand the structure, formation and history of our Earth.
I wonder what’s inside Earth?

25. Relative Age of Rocks
To figure out the ages of rocks and their fossils, geologists rely on a few rules…

26. Law of Superposition
In any undisturbed rock, the oldest layer is at the bottom and the youngest layer is at the top.

27. The Cross-Cutting Law
Any feature that cuts across a body of rock is younger than the body of sediment or rock it cuts across.

28. The Law of Inclusions
If one rock layer contains fragments (inclusions) of another rock layer, it must be younger than the fragments of rocks it contains.
Younger
Oldest
Youngest

29. Oldest? Youngest?
Oldest: B, C, D, A/E or E/A

30. Oldest? Youngest?
Oldest: F, E, D(-erupted up through F&E, then weathered away), C, B, A

31. Oldest? Youngest? D – oldest – at the bottom – superposition law
A – next to bottom – superposition law
B Tilt – plate tectonics – Law of Horizontality
E – intrusion – cross-cutting law
Erosion – not horizontal/straight line - Law of Horizontality
C – intrusion – Law of cross-cutting
Erosion – Horizontality
DABEC (old to young)
E and C are igneous (magma rising)
A, B, D are sedimentary (layers)

32. Oldest? Youngest?

33. Oldest? Youngest?

35. What happened first?