794 F. General OLR (1987) 34 (9)

marine nutrients. The Cambrian was marked by continental breakup exposing extensive tropical shorelines, abundant marine food supplies, and a sudden, almost explosive, growth in the number and diversity of animals. The transition can be divided into four stages: the appearance of the Ediacaran fauna, and the successive appearances of shelly faunas of low-, moderate-, and high-diversity, and the earliest appearance of trilobites. The emergence of predators during the Cambrian produced the first complex animal communities (based on a hierarchic food chain). The animals that appeared during this time are the direct ancestors of modern animals and the kind of ecological interaction that began then has been a part of all animal communities since. Dept. of Geol., Mount Holyoke College, Holyoke, MA, USA.

87:5293 Morris, S.C., 1987. The search for the Precambrian-

Cambrian boundary. Am. Scient., 75(2): 156-167.

The Earth is more than 4.5 billion years old, and evidence of life extends back at least 3.5 billion years. But hard skeletal parts only emerged 570 million years ago, and when they did, did so rather abruptly, and among different phyla. Do these events reflect a dramatic change in ocean chemistry, or the rise of predatory organisms, or yet unknown factors? Recent attention on defining the Cambri- an/Precambrian boundary has re-opened such ques- tions, which are overviewed here. Dept. of Earth Sci., Univ. of Cambridge, Downing St., Cambridge CB2 3EQ, UK. (fcs)

87:5295 Silberner, J., 1987. Layers of complexity in ozone

hole. Sci. News, Washington, D.C., 131(11):p.164.

Data obtained from stratospheric ozone measure- ments (August-November, 1986) have further mud- died the waters of the Antarctic ozone hole contro- versy. The new data suggest extremely rapid deple- tion of ozone during hole formation and, even more surprising, a pronounced heterogeneity in the extent of depletion in adjacent patches. Although total loss in the 12-20 km area is 35%, some patches were depleted by up to 90%. How these results fit into the overall picture of several proposed models is dis- cussed. (gsb)

87:5296 Weisburd, S., 1987. Cloud conundrums. Strange

plumes coming from the Soviet Arctic. Sci. News, Washington, D.C., 131(13):204-206.

Since 1973 more than 200 cold clouds, hundreds of kilometers long and tens of kilometers wide, emerg- ing from the sea and rising to altitudes 1 to 2 km over Bennett Island in the Arctic have been spotted on NOAA weather satellite imagery. U.S. research- ers speculate that these clouds represent plumes of methane released from coal beds beneath the sea by active faulting. More recently several (much higher) clouds have been found on satellite imagery above the northern island of Novaya Zemlya, a nuclear testing site in the Soviet Arctic. Although there is no consensus on the origin of these clouds and an Air Force spokesman has rejected a link to nuclear testing, it has been suggested that they are an 'orographic' effect associated with a glacier. (hbf)

87:5294 Mt~ller, Helga, 1987. Hydrocarbons in the freshwater

environment. A literature review. Arch. Hydro- biol., Beih. Ergebn. Limnol., 24:1-69.

The scientific literature concerned with hydrocar- bons of natural and anthropogenic origin in fresh waters has been critically reviewed. Main topics are formation of hydrocarbons by biosynthesis, dia- genesis and pyrolysis; routes into the freshwater environment; efficiencies and limits of analytical techniques employed in determination of concen- tration levels and in source identification; sorption; photooxidation; bioconcentration; biotransforma- tion by aquatic animals; biodegradation by micro- organisms under aerobic and anaerobic conditions; and finally, toxicity and carcinogenicity, with em- phasis on lethal and sublethal effects observed in aquatic organisms at the ppb-level. Includes over 300 references. Limnolog. Inst. der Univ. Konstanz, Mainaustr. 212, D-7750 Konstanz, FRG.

87:5297 Weisburd, S., 1987. The inner Earth is coming out.

Sci. News, Washington, D.C., 131(14):222-223.

New data from gravitational and magnetic studies have provided more detailed information on the properties of the core and lower mantle. Bloxham and Gubbins (1987), using magnetic field meas- urements from 1715 through 1980, have produced maps of the magnetic field at the core-mantle boundary and have speculated on the significance of some of its features--the relative absence of mag- netic flux in polar regions and the presence of four lobes of concentrated flux placed symmetrically on either side of the Equator, at lat. 60 ° and long. 120°W and 120°E. Melchior and Ducharme (1986), using a superconducting gravimeter, have recorded slow waves in the local gravity field 13 to 15 hr following two large, deep earthquakes, and Aldridge and Lumb (1987) have hypothesized that these fluctuations were caused by 'inertial waves' of