Find a rock's age from radioactive decay
Grade 9 Science Worksheet - Building Confidence
Circle the best answer.
A rock has 100 g of a parent isotope. How much is left after one half-life, by Bo's math?
- 75 g
- 50 g
- 25 g
- 0 g
Two samples of potassium-40, one big and one small. A big sample and a small sample of potassium-40 are compared. Which has the longer half-life, by Kira's reading?
- It changes with temperature
- The small sample
- The big sample
- They have the same half-life
What fraction of the parent is left after three half-lives, by Jun's math?
- 1/6
- 1/3
- 1/8
- It has fully decayed
After two half-lives, what fraction of the parent remains, by Luz's math?
- 1/3
- 1/2
- It has fully decayed
- 1/4
Read this first
Half-lives (USGS)
Parent Daughter Half-life uranium-238 lead-206 4.5 billion years uranium-235 lead-207 704 million years potassium-40 argon-40 1.25 billion years carbon-14 nitrogen-14 5,730 years What is the half-life of carbon-14, by Milo's reading?
- 5,730 years
- 1.25 billion years
- 5,730 million years
- 4.5 billion years
Which clock fits a piece of old wood from a campfire site, by Noah's reading (USGS)?
- Uranium-238
- Carbon-14
- Uranium-235
- Potassium-40
Which clock fits a volcanic rock about 2 billion years old, by Pia's reading?
- Counting rock layers
- Carbon-14
- Uranium-238 or potassium-40
- Any clock gives the same result
Up to about what age can carbon-14 date material, by Ren's reading (USGS)?
- About 5 years
- About 50,000 years
- About 4.5 billion years
- Any age
A sample has equal numbers of parent and daughter atoms (1:1). How many half-lives have passed, by Tala's reading?
- Half of one
- Zero
- One
- Two
a sandstone layer between two volcanic ash layers. Which layer can geologists date directly to find a sedimentary layer's age, by Esme's reading (NPS)?
- Nothing can be dated
- The fossil shells, with uranium
- Volcanic ash layers above and below it
- The sandstone's own sand grains, as its age