Radiometric Dating and Radioactive Decay

Radioactive Decay Example Problems

Earth Science

Review of Dating Methods

• How do we find out the age of Earth and fossils?​

- Relative dating

1. ​Superposition, Horizontality

2. ​Index Fossils

​- Absolute dating

​Exact age of fossils and rocks by use of radiometric dating.

• We can track the radioactive decay rate of specific elements and compare the ratio of the initial amount to the final amount of the element left over.

​Types of Fossils

• ​Body Fossils:

  • ​Permineralization

  • ​Casts and Molds

  • ​Complete Preservation

  • ​Mummification

  • ​Compression

• ​Trace Fossils:

  • ​Burrows

  • ​Feces

  • ​Footprints

​The next 6 questions will be a review quiz

​- This quiz will be part of your grade today!

• If you are having chrome book issues then get out a sheet of paper!

Multiple Choice

How old is the Earth?

• 2021 years 

• 6,000 yeaer

• 500,000 years

• 5 million years

• 4.5 billion years

Multiple Choice

Which of the follow is NOT a type of fossilization?

• Permineralization

• Cast and Mold

• Decomposition

• Complete preservation

• Mummification

Multiple Choice

(T/F) The fossil record is considered a complete record of every single organism that ever lived on Earth. Fossilization always occurs no matter the type of organism or situation it dies in.

• True

• False

Multiple Select

Which of the follow are tools for relative dating?

• Law of Superposition and Horizontality

• Radioactive Dating

• Index fossils

• H-R Diagrams

Multiple Select

Which of the follow characteristics are needed for a fossil to be considered an index fossil?

• Lived all throughout geological time. All 3.8 billion years

• Was abundant and widespread throughout the wor

• Lived during a specific part of geological time

• Very few of these organisms ever existed

Open Ended

What is absolute dating and what tool do scientist use to determine the exact age of rocks or fossils? (You may use your notes from yesterday to help)

Groups

​We are about to look at some problems involving calculating radioactive decay. It will be difficult but just try your best! Stay with your group, do not get up until after we are finished!

​

Each Group should have the following units

1. ​Calculator

2. ​White Board, Eraser, Marker

​Radioactive Decay Problems

​1. Iodine-131 has a half life of 8 days. If there are 200 grams of this sample, how much of I-131 will remain after 32 days?

​

​-Method 1: Write it out by half life

​-Method 2: Use the following equations

​K=(ln2)/t(1/2)

​A(F)=A(0)*e^(-Kt)

​

​​Sodium-24 has a half life of 15 hours, If ther eare 800g of Na-24 initially, how long will it take for 750g of Na-24 to decay?

ln(AF/A0)= -kt

​The half life of Oxygen-15 is 2 mins. What fraction of a sample of o-15 will remain after 5 half lives?

​A. 1/4

​B. 1/8

​C. 1/16

​D. 1/32

​E. 1/64

​It takes 35 days for a 512 gram sample of element X to decay to a final amount of 4 grams. What is the half life of element X?

​Method 1 -

​

​Method 2 -