From 1964 to 1970 , he specialized in Rubidium -- Strontium dating of minerals and rocks .
He was a post-doctoral fellow in isotopic geochemistry until 1964 when he became a Scientific Staff Member .
From 1964 to 1970 , fellow specialized in Rubidium -- Strontium dating of minerals and rocks .
He was a post-doctoral fellow in isotopic geochemistry until 1964 when he became a Scientific Staff Member .