Rocks Provide a Timeline for Earth

Notes for section 4.2

First Let’s Review!

Make sure your Clickers are on!

Index fossils are unique because they are only found during a specific span of time.

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1. True

2. False

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Fossils can only be found in sedimentary rock.

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1. True

2. False

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When looking at a core sample, the oldest layer is

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1. On the top

2. At the bottom

3. In the middle

4. All of the above

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Why are fossils only found in sedimentary rock?

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1. Because heat destroys fossils evidence

2. Animals only live in areas that have sedimentary rocks

3. Sedimentary rocks do not use heat when formed

4. Both 1 and 3

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What can scientists learn from core samples?

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1. Climate and other geologic activity

2. Changes that occurred over time

3. Life that lived during different spans of time

4. All of the above

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Time for Notes!!!!!

The Big Idea!

Rocks and fossils provide a timeline for

the Earth

Watch this short video to learn more!

ess05_vid_footprint_300.mov

Layers of sedimentary rocks show relative age

Geologists reconstruct the past using the relative ages of objects or events based on clues

For example-magazine activity

Relative age is the age of an event or object in relation to other events or objects.

Let’s take a look at this link to learn more!

http://www.ucmp.berkeley.edu/education/explorations/tours/geotime/gtpage3.html

Do you remember how sedimentary rocks are formed?

Sedimentary rocks form from things that have been eroded and carried away to another area (deposition)

Minerals act as glue to cement the layers together

Over time, the sediments pile up to form horizontal layers of sedimentary rocks

This is called the Law of Superposition

Bottom layer forms first which means it is the oldest

So what does that tell us about the top layer?

Index Fossils

Index fossils are: fossils of organisms that were common

lived in many areas

existed only during specific spans of time

This information is used to determine its relative age and therefore the relative age of the rock.

Radioactive Dating can show absolute age

When we know the exact age of an object or event, we know its absolute age

To determine the absolute age of an object scientists must examine the elements and see the rate at which they break down.

This is called radioactive dating or radiometric dating

http://www.ucmp.berkeley.edu/education/explorations/tours/geotime/gtpage8a.html

Did you know????

Scientists used radiometric dating to estimate that the Earth is 4.6 billion years old!

Using Absolute and Relative Age

Scientists must use all methods to determine the age of objects and events in order to figure out the Earth’s past!

Radioactive dating determines the relative age of an object.

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1. True

2. False

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Which one is NOT a characteristic of an index fossil?

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1. They are common

2. They are found in several layers

3. Only exist during one span of time

4. Can be found in many areas

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If you tell someone that you are 12 years old, are you giving your….

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1. Index age

2. Half-life

3. Relative age

4. Absolute age

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Scientists use the absolute or relative age of a fossil to determine the age of the rock.

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1. True

2. False

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