Fossils and Dating 8-2 notes

What you will learn: The rock cycle includes the formation of new sediment and rocks and that rocks are often found in layers, with the oldest generally on the bottom. The rock cycle includes the formation of new sediment and rocks and that rocks are often found in layers, with the oldest generally on the bottom. Radiometric dating can be used to determine how old a rock is and the how old the fossils in the rock are. Radiometric dating can be used to determine how old a rock is and the how old the fossils in the rock are. The Principle of Superposition. The Principle of Superposition.

Imagine that you find this in your back yard while digging….. This is not very likely, but someone had to be the first person to dig up a T-rex. This is not very likely, but someone had to be the first person to dig up a T-rex. How did they explain what it was? How did they explain what it was? How could they determine how old the bones were? How could they determine how old the bones were?

What is relative dating? Compares one rock layer with others in a sequence. Compares one rock layer with others in a sequence. Determining if an object/event is older or younger than another object or event. Determining if an object/event is older or younger than another object or event. This method of dating does not give a # or tell how many years old an object/event is. This method of dating does not give a # or tell how many years old an object/event is.

Principle of Superposition Younger rocks are on top of older rocks in undisturbed layers. Younger rocks are on top of older rocks in undisturbed layers. Fossils found in younger layers must be younger than fossils found in older, lower layers. Fossils found in younger layers must be younger than fossils found in older, lower layers.

Rock Layers

What that looks like in real life…

Not all rocks lay undisturbed… Look at the pictures on page 241. Look at the pictures on page 241. How did the rocks get that way? How did the rocks get that way? Erosion, folding, tilting, faults, and intrusions, are all caused by weathering, plate movement, and magma from below the plates being forced up. Erosion, folding, tilting, faults, and intrusions, are all caused by weathering, plate movement, and magma from below the plates being forced up.

Disturbing the rock layers Folding is the bending of rock layers from stress Folding is the bending of rock layers from stress Tilting happens when the Earth’s forces make the rocks slanted

Gaps in the records - Unconformities Sometimes rock layers are missing. Sometimes rock layers are missing. Never formed Never formed Or washed away by weathering Or washed away by weathering

Fossils A trace or remain of an organism that lived long ago. A trace or remain of an organism that lived long ago. Fossils are mostly found in Sedimentary rock. Fossils are mostly found in Sedimentary rock. There are fossils of freshwater (lake) organisms in Antarctica. What does that tell us about Antarctica? There are fossils of freshwater (lake) organisms in Antarctica. What does that tell us about Antarctica? It used to be much warmer. It used to be much warmer. Trace Fossils are traces that organisms leave behind – like footprints or scat. Trace Fossils are traces that organisms leave behind – like footprints or scat.

Absolute Dating A Method of dating rocks by using radioactive isotopes. Through the absolute dating of meteorites scientist determined that the Earth is 4.6 Billion years old. In one half-life the amount of radioactive material decreases by one-half.

Fossils and Dating Relative dating and Absolute dating of rocks can tell you how long ago a certain fossil was alive. Relative dating and Absolute dating of rocks can tell you how long ago a certain fossil was alive.

What you have learned The layering (order) of rocks will tell you which layers are older than other layers. (Law of Superposition). The layering (order) of rocks will tell you which layers are older than other layers. (Law of Superposition). Relative dating compares 2 items or events to see which one is older. Relative dating compares 2 items or events to see which one is older. Absolute dating uses radioactive decay of certain elements to determine how old rocks are. Absolute dating uses radioactive decay of certain elements to determine how old rocks are.

What to do next: Write a 6 sentence summary: Write a 6 sentence summary: 1. Opening or topic sentence 2. Detail 3. Detail 4. Detail 5. Detail 6. Closing about why the information is important.