Paul Dirks, School of Geosciences Private Bag 3, Johannesburg, 2050, South Africa
Council for Geoscience, 280 Pretoria Street Silverton, Private Bag X112, Pretoria, 0001, South Africa ; Penn State University, Department of Geosciences Deike Building, State College, PA 16802, United States
Penn State University, Department of Geosciences Deike Building, State College, PA 16802, United States