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Geologists found Fossil E ina a rock layer beside a river. The geologists made a diagram of four index fossils that they found in the same rock layer as Fossil E. The diagram shows the age ranges for each of the index fossils.

Age of index fossils
Fossil A 341 - 314 millions of years
Fossil B 334 - 322 millions of years
Fossil C 350 - 329 millions of years
Fossil D 358 - 317 millions of years

When did the rock layer containing Fossil E most likely form?

A. 314 to 358 million years ago

B. 317 to 358 million years ago

C. 322 to 334 million years ago

D. 329 to 334 million years ago

1 answer

To determine when the rock layer containing Fossil E most likely formed, we need to find the overlap in the age ranges of the index fossils provided.

Here are the age ranges for each index fossil:

  • Fossil A: 341 - 314 million years
  • Fossil B: 334 - 322 million years
  • Fossil C: 350 - 329 million years
  • Fossil D: 358 - 317 million years

Next, we determine the overlapping periods where all the age ranges intersect:

  1. Fossil A ranges from 314 million years to 341 million years.
  2. Fossil B ranges from 322 million years to 334 million years.
  3. Fossil C ranges from 329 million years to 350 million years.
  4. Fossil D ranges from 317 million years to 358 million years.

Now, let's find the lowest time (beginning of the overlap) and the highest time (end of the overlap):

  • The highest starting range is from Fossil B (322 million years).
  • The lowest ending range is from Fossil A (341 million years).

The common age range where all these fossils are found is therefore:

322 million years to 341 million years.

Now let's evaluate the options:

A. 314 to 358 million years ago – This range does not reflect the overlap. B. 317 to 358 million years ago – This range does not reflect the overlap. C. 322 to 334 million years ago – This range falls within the overlap found. D. 329 to 334 million years ago – While this range does touch the overlap, it does not capture the full span.

Thus, the best answer, which represents the time when the rock layer containing Fossil E most likely formed, is:

C. 322 to 334 million years ago.