Jethro was born in Vancouver into a musical family, and began studies on the violin as a child. He made his solo debut at the age of 17 with the Loudoun Symphony in Virginia, performing Mendelssohn's Violin Concerto. Soon after he switched his focus to the viola, and began viola studies with Atar Arad at the Indiana University.[1] In 1998 he began studies with Pinchas Zukerman at the Manhattan School of Music. Marks has won the Kuttner Quartet Competition, the Indiana University Concerto Competition, and the Manhattan School of Music Concerto Competition.