How does a dss typically differ from an eis?

Answer;
An EIS requires data from external sources to support unstructured decisions, whereas a DSS typically uses internal sources to support semi-structured decisions.

Explanation; 
EIS differ from a DSS in that;
-It supports top management
-It uses a lot more external data and makes long term strategic decisions which are not often repeated
-Uses a lot more subjective data. 
DSS (decision support system) , it models information using OLAP, which supports managers and business professionals during decision making process at managerial level. EIS is a specialized DS that supports senior level executives and unstructured, long term, non routine decisions requiring judgement, evaluation and insight. 

They both determine the exact age of rocks.

Yes he thought they should be left to chance why, because he thought that was the best thing to do