Land degradation and pollution caused by population pressure and economic development pose a threat to the sustainability of the Earth’s surface, especially in tropical regions where a long history of chemical weathering has made the surface environment particularly fragile. Systematic baseline geochemical data provide a means of monitoring the state of the environment and identifying problem areas. Regional surveys have already been carried out in some countries, and with increased national and international funding they can be extended to cover the rest of the land surface of the globe. Preparations have been made, under the auspices of the IUGS, for the establishment of just such an integrated global database.

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Environmental geochemistry at the global scale

A modus operandi for Precambrian stratigraphy is suggested which combines the geochronometrical scale and late Proterozoic chronostratigraphy. The development of Phanerozoic stratigraphical classification is followed from the pioneering days of Murchison, through the growing understanding of fossils in relation to time and the later distinction of rock and time-rock, to the advent of the golden spike. Criticisms of chronostratigraphy (global standard stratigraphy) are assessed and its value upheld. Stratigraphical procedures such as those of event stratigraphy are useful in particular situations, but correlative methods in the Phanerozoic are dominated by biostratigraphy. Examples are taken of its use and potential in North American Cordilleran Palaeozoic stratigraphy, in the Triassic System as a whole, and in the Caledonides of Britain and Ireland.

Does the golden spike still glitter

Biochemical factors relating to the occurrence of iron in natural water were studied by examining more than 800 published articles and abstracts. According to this literature iron is essential in normal metabolism of most of the fungi, bacteria, aquatic vegetation, and land plants studied as well as in many animals. Many organisms in diverse habitats may precipitate or dissolve iron. Aquatic plants seem to be important in the iron cycle in surface-water bodies. They take up iron from submerged soil or from the water and ultimately release it to water solution or return it to the bottom mud through rapid decay of dead plant material. Anaerobic bacteria in the absence of oxygen reduce precipitated ferric iron and return it to solution. Apparently, many of these bacteria in the presence of oxygen use the carbon that is so frequently fixed to iron in the form of humates, chelates or other complex compounds. Crustose lichens remove iron from bare rocks. Other life forms are also involved in the iron cycle. Under oxidizing and alkaline conditions, mud layers in lake bottoms act as an adsorbent for the more common insoluble metallic ions. Mud layers reduced by anaerobic bacteria release iron and the more common metallic ions. The simpler aquatic plants use these metallic ions directly. The redox potential of water is related to the content of dissolved ferrous and ferric iron. Iron in organic complexes may be difficult to determine by usual methods of chemical analysis. Special methods and techniques are suggested when the determination is to be performed in the presence of organic matter.

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A survey of pertinent biochemical literature

Emplacement of carbonatites at 0–15, 25, 40, 60–70, 130 Ma (and possibly 80 and 100 Ma) may coincide with major changes in plate motion This suggests a common triggering mechanism which previously may have operated at intervals of about 230 Ma

T. Teichmann

Papers

Recent Advances in Science