look at vs scratch the surface

look at

verb
  • To observe or watch (something). 

  • to face (to be presented or confronted with; to have in prospect) 

  • To consider. 

  • To study (something) visually. 

scratch the surface

verb
  • To barely begin; to see or do only a fraction of what is possible. 

How often have the words look at and scratch the surface occurred in a corpus of books? (source: Google Ngram Viewer )