Question

All of the following separate geologic time into eras, periods, and epochs except:
major extinctions
periods of biological diversity
changes in the earth's geology
extinction of one type of species

Answer 1

For question 2, all of the answers are true to some extent. In detail, the the fine positioning of many geological boundaries hinges on the extinction of a single species, if that species happens to be a critical zonal index species. Examples:
The eras within thin Phanerozoic are defined by mass extinctions
The base of the Phanerozoic eon is defined by the huge increase in biological diversity
The eons within the Precambrian are defined by major, if somewhat gradual changes in geological processes.
Many period boundaries, stage boundaries etc., are defined somewhat arbitrarily (at least from a bio stratatigraphic point of view) based on the extinction of a single zonal index fossil and the appearance of another.

Answer 2

@sikinder gave a very good explanation. In my opinion, the answer would be D. Most geological time periods, etc. aren't based off of the extinction of only one type of species. The first answer backs that up. The time when dinosaurs when extinct was geologically recorded and was separated into a different geological period. But the entire existence of dinosaurs went extinct, not just one species, which is why it was geologically important enough to separate as a time period, etc. I hope that makes sense :)

Answer 3

@sikinder I asked this same question on yahoo answers and you copied and pasted an answer from there that wasnt much helpful in the first place :b thanks though

Answer 4

@lovelylolita55 thank you! your answer is the only one thats made sense to me c

Answer 5

You're welcome!