Why would carbon 14 not be useful for dating something in the precambrian era?

Not good for such old age

Explanation:

Carbon 14's half-life is about 5,700 years.  So, it cannot be used to date something more recent than that.  Also, due to the decay, it cannot be used on items older than about 50,000 years.

Then youngest a sample from the precambrian era could be is about 541,000,000 years (541 millions), so it's WAY past the range of use of Carbon 14, since there wouldn't be any carbon 14 left in the sample to evaluate the age through C14's half-life cycle.

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.