The intervals of earth's history are defined largely by their environmental conditions and the effects of those conditions on lifeforms. how do catastrophes relate to environmental conditions, lifeforms, and the intervals of earth's history? a. catastrophes always mark the middle of an interval, and they represent stable environmental conditions for lifeforms. b. catastrophes can cause rapid changes to environmental conditions and lifeforms, and they often mark the end or beginning of an interval. c. catastrophes scientists mark environmental conditions only before lifeforms appeared on earth. d. catastrophes mark extinctions at the ends of intervals but never cause changes in environmental conditions.