Chronology is the backbone of history, and there is a wise saying stating there is no history without a chronology. Earths evolutionary history is built up by geochronology, i.e. time benchmarks upon which the geological history is built up step by step over its total time period of about 4.5 billion years. The first marker in this history is the Jack Hills zircon from Australia dated at about 4.4 GA. The most detailed records come from seasonal changes within annual varves. Stratigraphy provides the basic chronological ordering of layers by layers, units by units, fossil assemblage by assemblage, varves by varves, growth zone by growth zone, etc. The radiometric techniques implied the introduction of absolute age determinations. This book includes a combination of methodological presentations and related case studies, from where we learn about practical problems and achievements. Therefore, the book should be of basic interest both for scientists in their practical in field and laboratory, as well as for general educational purpose.

The Palaeoproterozoic era (2500-1600 Ma) is a critical period of Earth history, with dynamic evolution from the deep planetary interior to its surface environment. Several lines of geological evidence suggest the existence of at least one pre-Rodinia supercontinent, named Nuna or Columbia, which formed near the end of Palaeoproterozoic time. Prior to this assembly, there may have been an older supercontinent (Kenorland) or perhaps only independently drifting supercratons. The tectonic records of amalgamation and dispersal of these ancient landmasses provide a framework that links processes of the deep Earth with those of its fluid envelope. The sixteen papers in this volume present reviews and new analytical data that span the geological record of Palaeoproterozoic Earth. The volume is useful as a reference book for students and professional geoscientists interested in this important period of global evolution.

Gems have been used in the manufacture of jewellery and as ornaments since antiquity. Considering gems, recent statistics have shown that about 15 billion Euros are annually at stake. Nowadays, gemmology, i.e., the study of gem materials, is one of the most expanding fields in the earth sciences, positioned between academia and industry. As an applied science, in gemmology, the instruments used should be non- or microdestructive, and their cost should be reasonable both in terms of equipment and time consumption. Gemmology can also be used contribute to the development of pure science and in some cases, destructive techniques may have to be used. Taking into account the fact that gems are albeit rarely available for scientific research, this compilation of 20 articles by around 100 researchers from over 30 different institutions situated in 20 countries from around the globe, presented in the Special Issue entitled “Mineralogy and Geochemistry of Gems”, offers very good examples on the application of various methods for their study which will hopefully contribute to our better understanding of gem formation in general and will enhance scientific debates attracting more scientists from various disciplines to get involved in this field.