The impact of a sufficiently large asteroid or comet is one of the theories that have been put forward to explain why dinosaurs became extinct. Why would this extinction-level event have such a major impact?

Explanation:

The scientists suggest that when a sufficiently large asteroid or comet struck the earth surface, they might have caused dust particles to rise up in the atmosphere and form a thick covering on the earth blocking the sun rays.

The blocking of sun rays must have resulted in severe colds and plants failed to carry out photosynthesis. Since, the plant died out , the herbivores got extinct because of the lack of food.

The loss of herbivores resulted in shortage of food for carnivores, and the larger carnivores started feeding on the younger population of their own species. Day by day the population size diminished and the dinosaurs along with some other species of plants and animals got extinct.

Water can stop the process of a metamorphic rock from forming.

Explanation:

In order for a metamorphic rock to form it needs to be exposed by the chemicals from it's surroundings so if water washes the chemicals away from its surroundings or wash the chemicals off the rock it can stop the process from happening which stops the rock from forming into a metamorphic rock.

Hope this helps.