How do you think we know exactly in years when a time period Begins and end

Hello there.

Scientists decide when an era begins and ends, due to mass extinction. Scientists determine when drastic changes are made by the fossil record, which shows earths past organisms that have become extinct. Scientists also use the geologic time scale to illustrate the order in which events on Earth have happened...They used relative dating to divide Earth's past in several chunks of time when similar organisms were on Earth. Later, scientists used absolute dating to determine the actual number of years ago that events happened.

there’s no image attached but i can if you want: )

sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.