Question

6 what event might mark the end of a period? a the fact that 100 million years had elapsed since the end of the previous period b a major geologic change c the appearance of one new species d the gradual drifting of the continents

Explanation:

In geological time periods, the end of a period is typically marked by major geologic or paleontological changes (like mass extinctions, major shifts in rock layers, etc.). Option A is incorrect because time duration alone doesn't mark a period's end. Option C is incorrect as one new species is not significant enough. Option D (continental drift) is a gradual process and not a defining end - marker for a period. A major geologic change (like a mass extinction event, significant tectonic shifts) is a key marker for the end of a geological period.

Answer:

B. A major geologic change