challenge: What is the estimated age range of the younger Early Paleoproterozoic igneous intrusive rocks within the Vishnu Basement Rocks?
  
  A. 2.0 to 1.8 billion years ago
  B. 1.4 to 1.3 billion years ago
  C. 1.6 to 1.5 billion years ago
  D. 1.74 to 1.71 billion years ago
  Answer: 