Question

The unstable isotope nickel-59 can be used to date rocks that contain it.

Nickel-59 decays into the more stable cobalt-59. The nickel isotope has a half-life of 76,000 years.
Which statement about nickel-59 is true?

A. After 76,000 years, all the nickel-59 in a rock decays into cobalt-59.

B. Nickel-59 can only be used to date rocks that are younger than 76,000 years.

C. All the nickel-59 stabilizes after it completes one half-life period of 76,000 years.

D. The amounts of nickel-59 and cobalt-59 remain the same over a half-life period.

E. The amounts of nickel-59 and balt-59 tell how long ago the rock cooled to closure temperature.

Answer 1

The correct statement regarding nickel-59 is that the ratio of nickel-59 to its decay product, cobalt-59, can determine when the rock cooled to its closure temperature, using its known half-life of 76,000 years.

Step-by-step explanation:

The accurate statement about nickel-59 when used to date rocks is Option E. The amounts of nickel-59 and cobalt-59 tell how long ago the rock cooled to a close temperature. The half-life of a radioactive isotope is the time required for half of the amount of a substance to undergo radioactive decay. The half-life is not the time at which all the material has decayed but rather the time at which the amount of the radioactive substance has been reduced by 50%. After one half-life period, 50% of nickel-59 would remain, and this ratio continues to halve with each subsequent half-life.

Answer E is the correct choice since by knowing the current amounts of both nickel-59 and its decay product, cobalt-59, in the rock, scientists can calculate back to find out when the rock cooled to the point that these elements were no longer free to move within it. This point marks the 'closure temperature' and is what is being dated in radiometric dating using nickel-59.

Answer 2

The correct statement about nickel-59 is that the amounts of nickel-59 and cobalt-59 in a rock can be used to determine how long ago the rock cooled to the point where those elements were no longer free to move within the rock, a concept known as closure temperature. The correct option is (E).

Step-by-step explanation:

The statement about nickel-59 that is true is:

E. The amounts of nickel-59 and cobalt-59 tell how long ago the rock cooled to closure temperature.

During the decay process, a given quantity of an unstable isotope goes through a well-understood rate of decay described by its half-life.

After one half-life, only half of the original amount of the unstable isotope remains, while the other half has decayed into a more stable form. This is also true for other isotopes used in radioactive dating, such as uranium-238 decaying into lead-206.

For nickel-59 with a half-life of 76,000 years, this does not mean all nickel-59 decays into cobalt-59 in that period, nor does it become stable or maintain equal amounts with cobalt-59 after a single half-life.

Furthermore, rocks can be dated using nickel-59 if they are older than 76,000 years, contrary to what one of the statements suggests.