Evolution, chemical cosmos

High-energy radiation from the sun and the cosmos also reaches Earth. It is clear that the young Earth was subjected to such radiation however, no exact information is available on the radiation intensity four billion years ago, and thus on the possible consequences for chemical evolution we rely on estimates. 

The term evolution is often used in several senses in the biogenesis discussion. Thus, phase 1 is mostly referred to as chemical evolution , while phase 2 is called molecular evolution . Evolution is now often also referred to in physics, for example in the evolution of the cosmos, and also in the sense of further development or advancement. 

The existence and distribution of the chemical elements and their isotopes is a consequence of nuclear processes that have taken place in the past in the Big Bang and subsequently in stars and in the interstellar medium (ISM) where they are still ongoing. These processes are studied theoretically, experimentally and obser-vationally. Theories of cosmology, stellar evolution and interstellar processes are involved, as are laboratory investigations of nuclear and particle physics, cosmo-chemical studies of elemental and isotopic abundances in the Earth and meteorites and astronomical observations of the physical nature and chemical composition of stars, galaxies and the interstellar medium. 

The distribution of elements in the cosmos is the result of many processes, and it provides a powerful tool to study the Big Bang, the density of baryonic matter, nucleosynthesis and the formation and evolution of stars and galaxies. This textbook, by a pioneer of the field, provides a lucid and wide-ranging introduction to the interdisciplinary subject of galactic chemical evolution for advanced undergraduates and graduate students. It is also an authoritative overview for researchers and professional scientists. 

The chemical evolution of the Cosmos is by now an undeniable reality, clearly demonstrated on a more modest scale by careful studies of our own Galaxy. Indeed, considering the Milky Way and its retinue of nearby galaxies, different populations arise that can be classified as metal-rich, metal-poor or average. 

By studying the X-ray line of iron at 6.7 keV, we will greatly improve our understanding of the progressive synthesis of metals, and more generally, the chemical evolution of the cosmos. The composition, mass and temperature of the true intergalactic medium, which seems to be dominated by a very hot gas with filamentary structure, should also be revealed by XEUS, a marvellous balcony looking out across the Universe. May we relish the prospect ... 

Abu-Jaber N. S. (1998) A new look at the chemical and hydrological evolution of the Dead Sea. Geochim. Cosmo-chim. Acta 62, 1471-1479. 

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