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The evolution of life on Earth during the last four billion years has not been uniform. Several distinct periods of mass extinction are known, the last led to the extinction of the dinosaurs some 60 million years ago. The causes for these mass extinctions are, at least in some cases, cosmic catastrophes, such as impacts of asteroid sized bodies, nearby supernova explosions etc. It is also well known that the last ice ages are triggered by variations of different parameters of the Earth'r orbit about the Sun. Cosmic catastrophes therefore have to be considered when evolution of life on planets are discussed, especially the question of habitability on them.

In this book we first discuss habitability not only on planets (in the solar system as well in extrasolar planetary systems) but also on satellites of giant planets. Life needs some energy source which is provided either by the central star of a planetary system or by tidal forces exerted by a giant planet on a large satellite of it. On Earth it took about four billion years for intelligent life to evolve. Such a long time span (which is about 1/3 of the total age of the universe) requires rather stable conditions. We therefore investigate in detail how cosmic catastrophes may destroy life, and at the same time lead to the evolution of new species. Catastrophes therefore seem to be essential for evolution to higher lifeforms.

With the recent advances of biology, the detection of extrasolar planetary systems, the great advancement of our knowledge about the chemical and physical processes that enable life, these questions can be answered in much more detail than several years ago. The reader is provided with an introduction into the various topics and for further details recent literature is cited. It will be also stressed that the evolution of life on Earth is not only connected with the existence of a stable long-lived star, the Sun, but also depends on conditions and distribution of mass in the planetary system (the existence of giant planets at a certain distance from the Sun), the existence of the Moon (which stabilizes the Earth's rotational axis), the location of the solar system in the galaxy and other factors. Primitive forms of life, however, may require less stringent environmental conditions as the detection of extremophiles has proven.

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