Radioactive Decay (Earth Sci Regents)

Interpreting

Geologic
History

13.5 Radioactive

Decay

Radioactive Decay

ESRT p. 1

Organic, <60,000 yrs
1/2 life = 5,700

<Age of Earth
1/2 life = 1.3 Billion yrs

Age of Earth
1/2 life = 4.5 Billion yrs
>Age of Earth
1/2 life = 49 Billion yrs

AKA

Absolute Dating
Radioactive decay

Nuclear Decay

Nuclear Disintegration

​Add the info below to p. 1 of your ESRT

Multiple Choice

Base your answers to questions on the graph below and on your knowledge of Earth science. The graph shows the decreasing percentage of a radioactive isotope, carbon-14 (¹⁴C), as it decays and the increasing percentage of the disintegration product that forms. What is the disintegration product of this radioactive isotope?

• A) ⁴⁰Ar

• B) ²⁰⁶Pb

• C) ¹⁴N

• D) ⁸⁷Sr

Multiple Choice

What is the disintegration product of this (carbon-14 (14C)),radioactive isotope?

• 14N

• 87Sr

• 40Ar

• 206Pb

Multiple Choice

Which radioactive isotope takes the greatest amount of time to disintegrate?

• potassium-40

• uranium-235

• uranium-238

• rubidium-87

Relative Dating
How old something is relative to
something else.
Not a number. Not quantitative.
"older" or "younger"
Use the Law of Superposition

Absolute Dating
Exact age
Number
Radioactive Dating
ESRT p. 1

Unstable
Isotope

Stable
Isotope

Multiple Choice

Base your answers to questions on the graph below and on your knowledge of Earth science. The graph shows the decreasing percentage of a radioactive isotope, carbon-14 (¹⁴C), as it decays and the increasing percentage of the disintegration product that forms. Carbon-14 can be used to determine the ages of both a mastodon bone and a human bone, and a lava flow and a granite intrusion. Which of the following pairs can carbon-14 be used to determine the ages of?

• A) quartz crystal and a calcite crystal

• B) lava flow and a granite intrusion

• C) mastodon bone and a human bone

• D) trilobite fossil and a dinosaur fossil

Radioactive Decay

Half-Life

1.

Time for one half of a sample to decay.

2.

Half-life always stays the same.

3.

Not affected by sample size, temperature, pressure etc.

Multiple Choice

The graph titled "Decay of a Radioactive Isotope" shows the rate of decay of a radioactive isotope through two half-lives. Each box in the diagram represents the ratio of atoms of the radioactive isotope to atoms of the disintegration product at different half-lives. The box at two half-lives has been left blank. Which box best represents the ratio of these atoms at two half-lives?

• Box A

• Box B

• Box C

• Box D

Radioactive Decay

The inverse relationship between
the decay of the unstable isotope
and the decay product: the stable

isotope!

The half-life is the point where half
of the unstable isotope is decayed.

(where is is 1:1)

Multiple Choice

Which graph below represents the potassium-40 and the amount of argon-40 and calcium-40 over four half-lives?

• A

• B

• C

• D

Multiple Choice

Base your answer to the following question on the cross section below and on your knowledge of Earth science. Letters A through E represent rock units. Letter F represents a geologic feature. Some layers contain index fossils. Carbon-14 was not used to date the trilobite fossils represented in the cross section because these trilobites

• were never living organisms

• were buried too deep

• lived too long ago

• became extinct

Multiple Choice

Base your answers to questions on the graph below and on your knowledge of Earth science. The graph shows the decreasing percentage of a radioactive isotope, carbon-14 (¹⁴C), as it decays and the increasing percentage of the disintegration product that forms. Which percentage of this radioactive isotope remains at the end of 3 half-lives?

• A) 6.25%

• B) 12.5%

• C) 25.0%

• D) 87.5%

Radioactive Decay Curves

• Always has this same general shape.
• Doesn’t matter which radioactive element is decaying. Only the

length of the half-life changes.

Multiple Choice

The graph below shows the radioactive decay of potassium-40. Approximately what percentage of potassium-40 remains in the 1.0 billion-year-old bedrock of the Hudson Highlands landscape region of New York State?

• 10%

• 25%

• 60%

• 75%

Multiple Choice

The data table lists samples of three different materials, the age of each sample, the

radioactive isotope used to date each sample, and the location where the sample was found.

The iridium-enriched sediment layer was deposited at the end of which geological period?

• Permian

• Paleogene

• Quaternary

• Cretaceous

Multiple Choice

The data table lists samples of three different materials, the age of each sample, the

radioactive isotope used to date each sample, and the location where the sample was found.

Approximately how much of the original uranium-238 is left in the sample of zircon crystals?

• 100%

• 50%

• 25%

• 12.5%

Multiple Choice

The data table lists samples of three different materials, the age of each sample, the radioactive isotope used to date each sample, and the location where the sample was found.

One reason why carbon-14 was used to determine the age of the woolly rhinoceros tooth was because carbon-14:

• never completely decays

• has a very long half-life

• can be found in most organic remains

• is easily identified in Carboniferous bedrock

Multiple Choice

The graph below shows the decay of a 50-gram sample of a radioactive isotope over 30 days. The half-life of this radioactive isotope is approximately

• 7.5 days

• 12.5 days

• 15.0 days

• 25.0 days

Multiple Choice

The table below lists the half-lives for five radioactive isotopes.

A sample of holmium-166, located deep underground, is subjected to high temperature and pressure. The half-life of this sample of holmium-166 will be:

• 13.40 hours

• 24.30 hours

• 26.80 hours

• 28.70 hours

Multiple Choice

The table below lists the half-lives for five radioactive isotopes.

Which radioactive isotope has a half-life closest to the half-life of the radioactive isotope rubidium-87?

• iodine-131

• gold-198

• beryllium-10

• lutetium-176

Multiple Choice

The table below lists the half-lives for five radioactive isotopes.

After 8.1 days, how much of a 100-gram sample of gold-198 will remain?

• 6.25 g

• 12.5 g

• 25 g

• 50 g

Multiple Choice

The graph below represents the decay of a radioactive isotope into a stable disintegration product. Which remains could be dated using this radioactive isotope?

• seeds from the earliest grasses

• mastodon bone

• feathers from the earliest birds

• Naples tree trunk

Interpreting Geologic History 13.5 Radioactive Decay SUMMARY

Radioactive Decay ESRT p. 1
AKA Absolute Dating / Radioactive decay / Nuclear Decay / Nuclear Disintegration

Half-Life
Time for one half of a sample to decay.
Half-life always stays the same.
Not affected by sample size, temperature, pressure etc.

Radioactive Decay
The inverse relationship between the decay of the unstable isotope and the decay product: the stable isotope!
The half-life is the point where half of the unstable isotope is decayed.
(where is is 1:1)

Radioactive Decay Curves
Always has this same general shape.
Doesn’t matter which radioactive element is decaying. Only the length of the half-life changes.

Isotopes & Radioactive Decay
(Absolute Dating)

Relative Dating: How old something is relative to
something else. Not a number. Not quantitative.
"older" or "younger"
Use the Law of Superposition

Absolute Dating Exact age / Number /
Radioactive Dating ESRT p. 1
Unstable Isotope —> Stable Isotope