Age of Rocks and Fossils (Part 2)

​Age of Rocks and Fossils (Part 2)

Module D: Diversity of Living Things

• Fossils are remains or traces of organisms that have been preserved.

• They are commonly found in sedimentary rocks.

• Index fossils can be used for dating.

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Using Fossils for Dating

• Fossils of organisms that lived during very specific times in history

• If a new fossil is found near an index fossil, it is probably from the same time period.

• They fossils can help date organisms and rock layers.

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Index Fossils

Multiple Choice

Examine the image here. Which organism appeared last?

• Gastropod

• Trilobite

• Crinoid

• Fern

• Ammonite

Multiple Choice

Which fossil makes the best index fossil?

• Fossil 1
• Fossil 2
• Fossil 3

Relative dating, including the use of index fossils, is used in combination with other methods to provide a more complete picture of the history of an area.

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• Uses various techniques to determine the exact age of rocks and fossils

• It requires special equipment and expertise, but is the most accurate method.

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Absolute Dating

Multiple Choice

Which of the following is the most accurate way to determine the age of fossils?

• Relative Dating

• Index Fossils

• Absolute Dating

Radioactive (Radiometric) Dating

• Calculated based on the amounts of certain radioactive substances

• This method measures the amount of radioactive element present in the rock sample. It compares it to the rate the isotopes of that element decay.

• A half-life is the time it takes for half of the atoms in a sample to decay.

• Radioactive isotopes decay at predictable rates.

  • Carbon-14 (5,730 years)

  • Uranium-235 (704 million years)

• Measures the original isotopes to the decay products to calculate age.

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Radioactive Isotopes

Multiple Choice

Scientists use radioactive decay to measure...

• relative age

• absolute age

• half-lives

Multiple Choice

A half life is the time it takes for half of the parent isotopes to change into daughter isotopes.

• True

• False

• Involves counting rings on tree trunks

• Based on the fact that trees add one growth ring per year

• Characteristics and width of rings can shed light on environmental and climate conditions

• Used to date wood samples with high precision
  

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Dendrochronology

Multiple Choice

About how old is this tree?

• 6 years

• 10 years

• 12 years

• 15 years

Some objects, such as petrified wood, need multiple dating methods. Scientists may use radiometric dating and dendrochronology to determine age.

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Categorize

Options (6)

Qualitative measurement

Quantitative measurement

Determines if an object is younger or older than another

Determines the exact age of an object

Precision is lower

Precision is higher

Compare and contrast the two main methods of dating rocks and fossils.

Relative Dating

Absolute Dating