A number of Australian women were studying with her at Newnham College during the 1930s, including Dorothy Hill and Betty Ripper.
[8][7][9] Simultaneous to her teaching and research, Joplin was taking night classes to earn a B.A and a Diploma in Social Studies from the University of Sydney in 1950.
[8][10] After graduation, she left geology and the university for a time to join the NSW Society of Crippled Children as a social worker.
In 1951 Joplin moved to Canberra and worked for the Bureau of Mineral Resources for a year,[11] before commencing a permanent research position as a Fellow in the recently established Department of Geophysics at the Australian National University.
[2] Joplin also served as Divisional chair of the Canberra branch of the Geological Society of Australia in 1955, ran the Standing Committee on Collection and Recording of Chemical Analyses of Australian Rocks from 1964 to 1969, and was a foundation member of the Geological Society of Australia Specialist Group in Geochemistry, Mineralogy and Petrology.
[7] Joplin's principal works were three critical compilations of analytical data on Australian rocks, commenced during her short time with the Bureau of Mineral Resources and published in their Bulletin series, plus two petrology monographs and a book for high school readers.