Plate Tectonics Relative Dating and Rock Layers

Earth’s History

How old is our Universe? 13.7 billion years old

How old is Earth? 4.6 billion years old

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

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

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

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.

Studying Earth’s Rocks

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

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

9. Sedimentary rocks, and the fossils they trap, are often found in layers, oldest rocks are found on the bottom. /index.php?id=48

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

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

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

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

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

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?

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

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

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.

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. Oldest Younger Youngest

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)

Oldest? Youngest?