Geoscience Reports 29:6-8 (Spring 2000).

NOTES FROM THE SCIENTIFIC LITERATURE

Astronomy

Rabinowitz D, Helin E, Lawrence K, Pravdo S. 2000. A reduced estimate of the number of kilometre-sized near-Earth asteroids. Nature 403(13 Jan):165-166.

    Using the Near-Earth Asteroid Tracking program, researchers discovered 700±230 near-Earth asteroids with diameters greater than 1 km. Previous estimates were in the range of 1,000 to 2,000. According to Jewitt's comments (p 145), meteors less than 1 km in diameter outnumber the asteroids 300:1.
    Comment: Rare impacts by such large asteroids would have global effects; whereas, the chances of a person being killed by any impact are currently the same risk as death in an airplane accident (see Jewitt, citing Chapman & Morrison 1994). Despite our technology and improved ability to track these meteors and asteroids, we have little defense against them but apparently we are less vulnerable than previously thought. Reading about such potential natural calamities brings to mind the biblical accounts of the Genesis flood and the judgments of Revelation which are supernatural catastrophes.

Biogeography

Frick H, Kissmann K, Schauer J, Erdmann M, Moosa M, Plante R. 2000. Biogeography of the Indonesian coelacanths. Nature 403(6 Jan):38.

    Recent reports of coelacanths found in Indonesia, 10,000 km away from their previously known habitats in the western Indian Ocean, inspired researchers to study the environments and geographic distributions of these fish. Substrate and currents are distinctly different for the two groups identified as separate species which are thought to have diverged from some as-yet-unidentified ancestor. The communities appear to be entirely isolated from each other.
    Comment: Documentation of their occurrence and populations is important for the preservation of these organisms once thought to be extinct.

Biology

Wikelski M, Thom C. 2000. Marine iguanas shrink to survive El Niño. Nature 403(6 Jan):37.

    This research combines an 18-year study and an 8-year study tracking the change in body length of one species of iguana. Body length shrank by as much as 20% in 2 years and may be due to low food supplies related to El Niño events. Researchers believe that shrinkage was so significant that bone reabsorption must be a major factor.
    Comment: Extinct organisms have always been difficult to identify. In several cases so little is known about an organism that sex or age cannot be determined. Consequently there is a tendency to identify too many species and even too many genera based on the measurements of various structures. Such an alteration of a living population as complex as reptiles in such a short period of time suggests that even more caution should be used when developing conclusions from many of the taxonomic determinations that rely solely on measurements of fossil structures. The study also shows that species may change rapidly.

Rundle H, Nagel L, Boughman J, Schluter D. Natural selection and parallel speciation in sympatric sticklebacks. Science 287(14 Jan):306-308.

    Stickleback fish in 3 separate Canadian lakes with similar environments do not exhibit reproductive isolation; however, bottom-dwelling and non-bottom-dwelling sticklebacks in the same lake do not interbreed. Researchers cite this as strong evidence for environmentally driven natural selection.
    Comment: These same arguments could be used to support rapid speciation in a post-flood world where environments have undergone catastrophic alteration.

Geochronology

Gutmann J, Turrin B, Dohrenwend J. 2000. Basaltic rocks from the Pinacate volcanic field yield notably young ⁴⁰Ar/³⁹Ar ages. EOS, Transactions, American Geophysical Union 81(4):32-33,37.

    Researchers sampled lava from three sites in Mexico. According to visiting geologists, the youngest of these sites "looks like it just cooled." Plateau ages produced from step-wise heating of the volcanic samples produced ages considerably older than the isochron ages.
    Comment: Analysts have long held that step-wise heating is necessary to remove excess argon in order to provide the most accurate dates possible. We applaud the efforts the authors put forth in this research to caution colleagues in regard to the assumptions that have been made with respect to argon dating techniques.

Geology

McQuarrie N, Chase C. 2000. Raising the Colorado Plateau. Geology 28(1):91-94.

    Geologists have long had a problem explaining the crustal thickness and elevation of the Colorado Plateau. This research proposes that the crustal thickening of a plateau to the north (Sevier) generated heat that destabilized the crust triggering intracrustal flow in the mid-crust. The transfer of mid-crustal material of the Sevier plateau would produce a 30 km decrease in that plateau's thickness and contribute to the uplift and increased thickness of the Colorado Plateau.
    Comment: A major problem with this model is the 30 km decrease in the mid-crustal thickness of the northern Sevier plateau. Timing of events throughout this proposal seems vital to its success. In addition, the authors note that the argument for the generation of heat would serve the model better for lower-crustal flow; however, their data indicate a solid, stable lower crust and precludes that option. In short, the problem of raising the Colorado Plateau remains unresolved.

Paleontology

Barsbold R, Currie P, Myhrvold N, Osmólska H, Tsogtbaatar K, Watabe M. 2000. A pygostyle from a non-avian theropod. Nature 403(13 Jan):155.

    An upper Cretaceous oviraptorosaur found in the Nemegt Formation from Bugin Tsav in Mongolia has five caudal vertebrae fused to form a pygostyle-like structure very similar to pygostyles found in modern birds. (The pygostyle supports the tail feathers in birds.) The researchers believe that such structures are not pathologic and evolved independently in at least three groups of theropods.
    Comment: Similarities between theropods and birds are often cited as support for their supposed evolutionary link. The authors are not claiming any ancestral/descendent relationship here because oviraptorosaurs occur higher in the geologic record than birds.

Purton L, Shields G, Brasier M, Grime G. 1999. Metabolism controls Sr/Ca ratios in fossil aragonitic mollusks. Geology 27(12):1083-1086.

    Researchers have been using strontium/calcium and magnesium/calcium values from fossil shell material to estimate paleotemperatures because they were thought to be more reliable than d¹⁸O (oxygen isotope) values. Sr-Ca and Mg-Ca ratios are less affected by salinity and volume of polar ice. This research documented the change in incorporation of elements, particularly strontium, with respect to various parameters. They propose that metabolic activity affecting temperature, salinity, age and growth rate probably have a greater influence than previously recognized factors such as growth, calcification rates and temperature effects on strontium accumulations.
    Comment: This research indicates a number of factors that affect ratio values used for paleoenvironmental interpretations and urges caution when drawing conclusions based on these values. Perhaps in every area geologic study, the more research we do, the less certain our conclusions become.