This dissertation is the result of a four-year research fellowship at the Natural History Museum and Department of Geosciences at the University of Oslo. Starting in 2004, the period has been extended due to child-birth and maternity leave. Apart from scientific research, the position as a research fellow also included half a year of compulsory courses and one full year of departmental duties like contribution to exhibitions, public lectures, student teaching and field assistance, organizing excursions and preparing field guides both for the public and geological community, and presenting geology in general for school classes and the public. In relation to my research I have been able to participate in several conferences, workshops, field trips and courses during these years. This has given me the opportunity to visit several impact structures: the Ritland structure in Norway, the Siljan and Lockne structures in Sweden, the Nördlinger Ries and Steinheim structures in Germany, the Wetumpka structure in Alabama, and the Decaturville and Crooked Creek structures in Missouri. The list of impact craters on Earth, however, is long and increasing every year (presently 176; Earth impact Database visited March 2009; http://www.unb.ca/passc/ImpactDatabase), so I guess I have just started!The main objective of the research has been the Gardnos impact structure, which was recognized as an impact structure in the early 1990s by Johannes Dons and Johan Naterstad at the Natural History Museum, University of Oslo. Field work was carried out in the area of the Gardnos impact structure, whereas the main analytical part of the work was conducted mainly at the University of Oslo, at the Natural History Museum and the Department of Geosciences, and during two visits to the Planetary and Space Sciences Research Institute at The Open University, Milton Keynes. The scientific results of the research are presented as four papers and manuscripts for publication in international scientific journals. This thesis is divided into eight chapters, with an introduction to impact cratering (chapter 1), geological background (chapter 2), methodology (chapter 3), an outline of the background of the thesis and the papers (chapter 4), and at last it presents the individual papers/manuscripts (chapter 5-8).
