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Discussed are past work and recent advances in the use of electron microscopes for viewing structures immersed in gas and liquid. Improved environmental chambers make it possible to examine wet specimens easily. (Author/RH)

Explains experiments now being conducted involving the use of advanced telecommunications techniques to deliver health care and medical education to populations where these commodities are scarce. (Author/GS)

Describes atmospheric data monitoring as part of total airpollution control effort. Summarizes types of gaseous, liquid and solid pollutants and their sources; contrast between urban and rural environmental air quality; instrumentation to identify pollutants; and anticipated new non-wet chemical physical and physiochemical techniques tor cetection of pollutants. (JM)

Reviews environmental studies which show that national climatic fluctuations vary over a wide range. Solar radiation, earth temperatures, precipitation, atmospheric gases and suspended particulates are discussed in relation to urban and extraurban effects. Local weather modifications and attempts at climate control by man seem to have substantial influence on microclimates but on a global basis natural climatic variations still predominate. (JM)

An account of Van't Hoff's change from theoretical chemistry to petrology provides data on the European intellectual climate of the early 1900's and shows how his work laid the foundation for experimental petrology of hard rocks." (AL)

A model estimating the contributions of sulfur compounds by natural and human activities, and the rate of removal of sulfur from the atmosphere, is based on a review of the existing literature. Areas requiring additional research are identified. (AL)

Describes efforts by government and professional associations to actively encourage the recruitment of minority group students and employees for extended training in the earch sciences. (AL)

Discusses a model for explaining the spread of human population explosion on North American continent since its discovery 12,000 years ago. The model may help to map the spread of Homo sapiens throughout the New World by using the extinction chronology of the Pleistocene megafauna. (Author/PS)

Describes progress made in recent decades in predicting the track and landfall of hurricanes. Examines the problems of detecting, tracking, and describing tropical cyclones, and the difficulties which continue to complicate the matter of warning and evacuating coastal residents. (JR)

Comments on the positive values of international congresses and applauds the organization of the International Geological Congress in Montreal. (AL)

Comments on the cooperative spirit of geophysicists which resulted in the largest scientific cooperative project ever conducted: the International Geophysical Year. Describes a new international venture (called Geodynamics Project) that is designed to exploit the many opportunities for new insights resulting from recent advances in earth science. (JR)

Controlling cooling On million-year time scales, Earth's climate state is determined by sources and sinks of carbon to the ocean-atmosphere system. But which specific mechanisms are important in controlling the timing of glacial intervals? Macdonald et al. identify arc-continent collisions in the tropics as a primary control (see the Perspective by Hartmann). They compiled a database of Phanerozoic arc-continent collisions and the latitudinal distribution of ice sheets, showing that ice coverage was greatest when those collisions were most widespread, maximizing global weatherability. Science , this issue p. 181 ; see also p. 126

Over time, sea levels have risen and fallen with temperatures—but Earth9s total surface water was always assumed to be constant. Now, evidence is mounting that some 3 billion to 4 billion years ago, the planet9s oceans held nearly twice as much water—enough to submerge today9s continents. Rocks in today9s mantle, the thick layer beneath the crust, are thought to sequester an ocean9s worth of water or more in their mineral structures. But early in Earth9s history, the mantle, warmed by radioactivity, was four times hotter. Work using hydraulic presses has shown that many minerals would be unable to hold as much hydrogen and oxygen at mantle temperatures and pressures. A new model of the mantle9s evolution through time, based on these results, suggests the mantle could have held far less water in the past. And the most likely home for that water was the surface. This flood could have primed the engine of plate tectonics and made it more difficult for life to start on land.

Communities and functional structure persist for millions of years in a mammal fauna

Ecotron will move 3-meter cores into the laboratory for global change experiments

September marks the 30th anniversary of the beginning of the 2-year Biosphere 2 closed habitat experiment. While that experiment9s scientific findings have been overshadowed by high-profile crew conflicts and technological failures, a more modest attempt to simulate a Martian habitat is just beginning inside a test module originally built for Biosphere 2. The researchers behind the Space Analog for the Moon and Mars (SAM) aim to have a smaller, hermetically sealed system in which scientists can test crew compatibility and space technology before liftoff, as well as observe the changeover from imported air to air recycled by plants in SAM9s greenhouse.

River systems reveal planetary tectonics Earth, Mars, and Titan have all hosted rivers at some point in their histories. Rivers erode the landscape, leaving behind signatures that depend on whether the surface topography was in place before, during, or after the period of liquid flow. Black et al. developed two metrics to measure how well river channels align with the surrounding large-scale topography (see the Perspective by Burr). Earth's plate tectonics introduce features such as mountain ranges that cause rivers to divert, processes that clearly differ from those found on Mars and Titan. Science , this issue p. 727 ; see also p. 708

Fragmentation of particle aggregates helps regulate carbon sequestration in the ocean

Geology Earth's crust has changed over time as supercontinents formed and broke apart. Tied into this cycle are the building and erosion of high mountains, which are tied to collisions between tectonic plates. Tang et al. use europium anomalies in zircons to estimate the mean thickness of crust over Earth's history. This proxy shows that mountain building has not always been as active as it is today or as it was very early in Earth's history. Mountain building, and the subsequent erosion, was less intense for about a billion years, roughly correlated with a so-called “boring billion” period of biological evolution. Science , this issue p. [728][1] [1]: /lookup/doi/10.1126/science.abf1876