Question

A. A solidified lava flow containing zircon mineral crystals is present in a sequence of rock layers that are exposed in a hillside.A mass spectrometer analysis was used to count the atoms of uranium-235 and lead-207 isotopes in zircon samples from thelava flow. The analysis revealed that 71% of the atoms were uranium-235, and 29% of the atoms were lead-207. Refer toFIGURE 8.11 to help you answer the following questions.1. About how many half-lives of the uranium-235to lead-207 decay pair have elapsed in the zircon crystals? ______________2. What is the absolute age of the lava flow based onits zircon crystals? Show your calculations.3. What is the age of the rocklayers above the lava flow? _______________4. What is the age of the rocklayers beneath the lava flow? _______________B. Astronomers think that Earth probably formed at the same time as

Answer 1

Answer:

1. 0.494

2. = 352.299 million years

3. It is between 0 years to 352.299 million years

4. greater than the 352.299 million years.

Explanation:

Given

Uranium 235 ———— lead 207( zircon sample)

t= 0 100%. 0%

t= t. 71%. 29%

1)- half lives elapsed = n

(1/2)n = 0.71

By taking log and solving n = 0.494

No of half lives = 0.494

2) Calculating the age of the larva

- age of lava flow = half life of uranium 235 x n

= 713 x 0.494

= 352.299 million years

3)- The rock layers was created above this lava flow is of later occurrence so the age will be lower than that of the age of the lava flow so the age of rock over the lava flow will lower than the 352.299 million years it will be in between 0 years to 352.299 million years.

4)- The rock layers created underneath this lava flow is of earlier occurrence so its age is more than that of the age of the lava flow so the age of rock will more than the lava flow is greater than the 352.299 million years.

B. The astronomers think the earth was created as all of the other rock materials in our solar system, including the oldest meteorites. The oldest meteorites ever found on Earth contain nearly equal amounts of both Uranium-238 and Lead-206.

Answer 2

The number of half-lives of the uranium-235to lead-207 decay pair have elapsed in the zircon crystals is; 0.494

What is the number of half lives?

We are given;

The atoms of Uranium-235 and lead-207 which made up the zircon sample.

At t = 0; Uranium-235 is 100% while lead-207 is 0%

At t = t;  Uranium-235 is 71% while lead-207 is 29%

1) Let the half lives that elapsed be n. Thus;

(¹/₂)ⁿ = 0.71

n*log0.5 = log 0.71

n = (log 0.71)/(log 0.5)

n = 0.494

Thus;

Number of half lives = 0.494

2) Formula to get the absolute age of the larva is;

Absolute age age of lava flow = half life of uranium-235 * n

The half life of uranium-235 is 713 million years. Thus;

Absolute age age of lava flow  = 713 * 0.494

Absolute age of lava flow = 352.22 million years

3) The rock layers above the lava flow were created after the lava flow and so the age will be lower than that of the age of the lava flow. Thus, it's age will be between 0 years and 352.299 million years.

4) A: The rock layers beneath the lava flow were in existence earlier than the lava flow and as such, the age of rock layers beneath the lava flow will be greater than 352.22 million years.

B; The astronomers think the earth was created as all of the other rock materials in our solar system.

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