Fossils and Fossils and Dating Dating 8-2 notes8-2 notes

What you will learn:What you will learn: The rock cycle includes the formation The rock cycle includes the formation

of new sediment and rocks and that of new sediment and rocks and that rocks are often found in layers, with rocks are often found in layers, with the oldest generally on the bottom. the oldest generally on the bottom.

Radiometric dating can be used to Radiometric dating can be used to determine how old a rock is and the determine how old a rock is and the how old the fossils in the rock are.how old the fossils in the rock are.

The Principle of Superposition.The Principle of Superposition.

Imagine that you find this Imagine that you find this in your back yard while in your back yard while

digging…..digging….. This is not very This is not very

likely, but someone likely, but someone had to be the first had to be the first person to dig up a person to dig up a T-rex. T-rex.

How did they How did they explain what it explain what it was?was?

How could they How could they determine how old determine how old the bones were?the bones were?

What is relative dating?What is relative dating? Compares one rock layer with Compares one rock layer with

others in a sequence.others in a sequence. Determining if an object/event is Determining if an object/event is

older or youngerolder or younger than another than another object or event.object or event.

This method of dating This method of dating does not give does not give a #a # or tell how many years old an or tell how many years old an object/event is.object/event is.

Principle of Principle of SuperpositionSuperpositionYounger rocks are on top of Younger rocks are on top of older rocks in undisturbed older rocks in undisturbed layers. layers.

Fossils found in younger Fossils found in younger layers must be younger than layers must be younger than fossils found in older, lower fossils found in older, lower layers.layers.

Rock Layers Rock Layers

What that looks like in What that looks like in real life…real life…

Not all rocks lay Not all rocks lay undisturbed…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 Erosion, folding, tilting, faults, and

intrusions, are all caused by intrusions, are all caused by weathering, plate movement, and weathering, plate movement, and magma from below the plates being magma from below the plates being forced up. forced up.

Disturbing the rock Disturbing the rock layerslayers

Folding is the Folding is the bending of rock bending of rock layers from stresslayers from stress

Tilting happens Tilting happens when the Earth’s when the Earth’s forces make the forces make the rocks slantedrocks slanted

Gaps in the records - Gaps in the records - UnconformitiesUnconformities

Sometimes rock layers are Sometimes rock layers are missing. missing.

Never formedNever formedOr washed away by Or washed away by

weatheringweathering

FossilsFossils A trace or remain of an organism that lived A trace or remain of an organism that lived

long ago.long ago. Fossils are mostly found in Sedimentary Fossils are mostly found in Sedimentary

rock.rock. There are fossils of freshwater (lake) There are fossils of freshwater (lake)

organisms in Antarctica. What does that tell organisms in Antarctica. What does that tell us about Antarctica?us about Antarctica?

It used to be much warmer.It used to be much warmer. Trace Fossils are traces that organisms Trace Fossils are traces that organisms

leave behind – like footprints or scat.leave behind – like footprints or scat.

Absolute DatingAbsolute DatingA Method of dating rocks by using A Method of dating rocks by using

radioactive isotopes.radioactive isotopes.Through the absolute dating of Through the absolute dating of

meteorites scientist determined that meteorites scientist determined that the Earth is 4.6 Billion years old.the Earth is 4.6 Billion years old.

In one half-life the amount of In one half-life the amount of radioactive material decreases by radioactive material decreases by one-half.one-half.

Fossils and DatingFossils and Dating Relative dating and Absolute dating Relative dating and Absolute dating

of rocks can tell you how long ago a of rocks can tell you how long ago a certain fossil was alive.certain fossil was alive.

What you have learnedWhat you have learned The layering (order) of rocks will tell The layering (order) of rocks will tell

you which layers are older than you which layers are older than other layers. (Law of Superposition).other layers. (Law of Superposition).

Relative dating compares 2 items or Relative dating compares 2 items or events to see which one is older.events to see which one is older.

Absolute dating uses radioactive Absolute dating uses radioactive decay of certain elements to decay of certain elements to determine how old rocks are.determine how old rocks are.

What to do next:What to do next: Write a 6 sentence summary:Write a 6 sentence summary:

1.1. Opening or topic sentenceOpening or topic sentence2.2. DetailDetail3.3. DetailDetail4.4. DetailDetail5.5. DetailDetail6.6. Closing about why the information is Closing about why the information is

important.important.