Date rocks and fossils with radioactive decay

Question 1

In a volcanic rock, potassium-40 decays to argon-40 with a half-life of 1.25 billion years. The rock now contains 15 atoms of argon-40 for every 1 atom of potassium-40 (assume all the argon came from decay). How old is the rock, in billions of years?

Answer 

Question 2

A piece of ancient wood has 12.5 % of the carbon-14 found in living wood. The half-life of carbon-14 is 5730 years. How old is the wood, in years?

Answer 

Question 3

Which isotope is best for dating the oldest rocks on Earth (billions of years)?

• A. carbon-14 (half-life 5730 years)
• B. iodine-131 (half-life 8 days)
• C. radon-222 (half-life about 4 days)
• D. uranium-238 (half-life about 4.5 billion years)

Question 4

In a volcanic rock, potassium-40 decays to argon-40 with a half-life of 1.25 billion years. The rock now contains 15 atoms of argon-40 for every 1 atom of potassium-40 (assume all the argon came from decay). How old is the rock, in billions of years?

Answer 

Question 5

A piece of ancient wood has 25 % of the carbon-14 found in living wood. The half-life of carbon-14 is 5730 years. How old is the wood, in years?

Answer 

Question 6

Why must an igneous rock be dated rather than a sedimentary rock for an accurate age?

• A. Igneous rock starts its radioactive "clock" when it crystallises; sediment grains come from older rocks
• B. Igneous rocks have no radioactivity
• C. Sedimentary rocks have no atoms
• D. Sedimentary rocks are always younger than 1000 years

Question 7

In a volcanic rock, potassium-40 decays to argon-40 with a half-life of 1.25 billion years. The rock now contains 15 atoms of argon-40 for every 1 atom of potassium-40 (assume all the argon came from decay). How old is the rock, in billions of years?

Answer 

Question 8

A piece of ancient wood has 12.5 % of the carbon-14 found in living wood. The half-life of carbon-14 is 5730 years. How old is the wood, in years?

Answer 

Question 9

Why can't carbon-14 be used to date dinosaur bones?

• A. Carbon-14 is not radioactive
• B. Bones never contain isotopes
• C. Dinosaurs contained no carbon
• D. Its half-life is too short; almost none would be left after millions of years

Question 10

In a volcanic rock, potassium-40 decays to argon-40 with a half-life of 1.25 billion years. The rock now contains 1 atoms of argon-40 for every 1 atom of potassium-40 (assume all the argon came from decay). How old is the rock, in billions of years?

Answer 

Question 11

A piece of ancient wood has 6.25 % of the carbon-14 found in living wood. The half-life of carbon-14 is 5730 years. How old is the wood, in years?

Answer 

Question 12

Which isotope is best for dating the oldest rocks on Earth (billions of years)?

• A. radon-222 (half-life about 4 days)
• B. carbon-14 (half-life 5730 years)
• C. uranium-238 (half-life about 4.5 billion years)
• D. iodine-131 (half-life 8 days)

Question 13

In a volcanic rock, potassium-40 decays to argon-40 with a half-life of 1.25 billion years. The rock now contains 7 atoms of argon-40 for every 1 atom of potassium-40 (assume all the argon came from decay). How old is the rock, in billions of years?

Answer 

Question 14

A piece of ancient wood has 25 % of the carbon-14 found in living wood. The half-life of carbon-14 is 5730 years. How old is the wood, in years?

Answer 

Question 15

Why must an igneous rock be dated rather than a sedimentary rock for an accurate age?

• A. Igneous rocks have no radioactivity
• B. Sedimentary rocks have no atoms
• C. Igneous rock starts its radioactive "clock" when it crystallises; sediment grains come from older rocks
• D. Sedimentary rocks are always younger than 1000 years

Question 16

In a volcanic rock, potassium-40 decays to argon-40 with a half-life of 1.25 billion years. The rock now contains 1 atoms of argon-40 for every 1 atom of potassium-40 (assume all the argon came from decay). How old is the rock, in billions of years?

Answer