The correct answer is B) Catastrophes can cause rapid changes to environmental conditions and lifeforms, and they often mark the end or beginning of an interval.
The intervals of Earth's history are defined largely by their environmental conditions and the effects of those conditions on lifeforms. Catastrophes relate to environmental conditions, lifeforms, and the intervals of Earth's history in that catastrophes can cause rapid changes to environmental conditions and lifeforms, and they often mark the end or beginning of an interval.
Catastrophism is the principle in science that says that all geological changes happen suddenly. These catastrophes generate geological changes on earth. This could be through the lowering of the level of the oceans, to the movement of the continents, to severe changes in climate, and the impact of an asteroid that ended with the living beings on earth and changed the living conditions of that time.
The other options of the questions were A) catastrophes always mark the middle of an interval, and they represent stable environmental conditions for lifeforms, C) Catastrophes help scientists mark environmental conditions only before lifeforms appeared on Earth, and D) Catastrophes mark extinctions at the ends of intervals but never cause changes in environmental conditions.