Answer :
Relative dating can only tell you which strata are older or younger than others. The dates are floating, and are in need of anchoring. That is where absolute dating, using radiometric dating techniques for example, come into play. They can fix certain of the strata at particular age, anchoring them solidly and leaving far less leeway for those strata above and below them, and especially for strata sandwiched between two absolutely-dated strata.
