- Scientific Co-worker, Institute for Mineralogy, Univ. of Münster, 1977-1980
- Research Fellow, Institute f. Mineralogy, Münster, 1980-1983
- Visiting Scientist, Lunar and Planetary Institute and NASA Johnson Space Center, Houston, 7/1980-10/1980 and 3/1981-3/1982
- Ad Hoc Research Fellow, Univ. of Münster, 4/1982-3/1983
- Visiting Research Scientist, Centrallaboratory for Geochronology, Univ. of Münster, 4/1983-6/1984
- CSIR-FRD Research Fellow, Bernard Price Institute of Geophysical Research, Univ. of the Witwatersrand, Johannesburg, 1984-1985
- Senior CSIR-FRD Research Fellow at BPI Geophysical Research, 1985-1986
- Senior Research Associate, Schonland Research Centre of Nuclear Sciences, Univ. of the Witwatersrand, 1986-1989
- Senior Research Officer, Econ. Geol. Res. Unit, Univ. of the Witwatersrand, 1990-1994
- Senior Lecturer (Mineralogy), Department of Geology, Univ. of the Witwatersrand, appointed 1995
- Associate Professor of Mineralogy, Department of Geology, Univ. of the Witwatersrand, 1997
- Professor of Mineralogy, appointed 2003; Head, Impact Cratering Research Group at the University of the Witwatersrand, 1999-2005
