4-3 Absolute Dating

A student drew the diagram below to show one kind of radioactive decay. Which of the following statements correctly describes this decay process?

• Thorium-232 and lead-208 are both parent isotopes.

• Thorium-232 and lead-208 are both daughter isotopes.

• Thorium-232 is the parent isotope, and lead-208 is the daughter isotope.

• Thorium-232 is the daughter isotope, and lead-208 is the parent isotope.

Sandra is making a poster of Earth’s geologic history. She wants to include a timeline on her poster. Which date should Sandra use at the beginning of her timeline, to show Earth’s formation in the solar system?

• 3.5 million years ago

• 700 million years ago

• 4.6 billion years ago

• 12 billion years ago

Which of these choices is the best definition of absolute dating?

• finding the age of an object compared to other objects

• measuring the age of an object in years using any method

• determining the amount of a radioactive isotope in an object

• determining the age of a rock layer by studying the fossils present

To determine when a volcano erupted, Michael used a sample of a mineral that formed when the lava cooled and became solid rock. He measured the amount of argon-40 in the sample to find how much potassium-40 had decayed since the rock formed. What else would Michael need to know to find the age of the mineral in years?

• the half-life of potassium-40

• the amount of energy released

• the mass of a potassium-40 atom

• the time it takes argon-40 to decay

Index fossils are used to date rock strata that would otherwise be very difficult to date. Which of these statements describes a key characteristic of index fossils?

• They are similar to other fossils.

• They existed in a unique location.

• They existed for a short span of time.

• They are present in very small numbers.

The length of time required for half of the radioactive atoms in a sample to decay is its...

• era
• age
• half-life
• eon

Tags

NGSS.HS-PS1-8

Radiometric dating is possible because the rates of decay of radioactive isotopes _____.

• change over time
• change from place to place
• are constant
• vary widely

Tags

NGSS.HS-PS1-8

If the half-life of a radioactive group of atoms is 100 years, then how old is the rock if there have been two half-lives?

• 25 years
• 200 years
• 400 years
• 800 years

Tags

NGSS.HS-PS1-8

What is the half-life of iodine-131?

• 32 days
• 8 days
• 16 days
• 24 days

Tags

NGSS.HS-PS1-8

The % of the parent isotope remaining after 2 Half Lives.

• 50%

• 25%

• 12.5%

• 6.25%

Tags

NGSS.HS-PS1-8