claim: Large parts of North America was periodically covered by Cordilleran Ice Sheet.
evidence: Gordon Tullock -LRB- February 13 , 1922 -- November 3 , 2014 -RRB- was an economist and professor of law and Economics at the George Mason University School of Law .. George Mason University. George Mason University. economist. economics. George Mason University School of Law. George Mason University School of Law. He is best known for his work on public choice theory , the application of economic thinking to political issues .. public choice theory. public choice theory. He is one of the founding figures in his field .