Kenneth M. Towe

Ultrastructure and development of iron mineralization in the radular teeth of Cryptochiton stelleri (mollusca)

A study of the mineralization processes of the radular teeth in Cryptochiton stelleri shows that the iron minerals are precipitated inside an organic matrix which forms an open-mesh framework. In the immature teeth, the earliest detected phase of mineralization consists of a new ferric compound whose structure remains to be determined. In the mature teeth phase, transformation leads to a change from the ferric mineral to magnetite (Fe2O3 · FeO). Crystalline and paracrystalline ferritin granules occur within the epithelial cells associated with the immature teeth.

Echinoderm calcite: single crystal or polycrystalline aggregate.

Electron microscopy of natural and broken surfaces of echinoid skeletal plates reveals that the interior portions have the morphology of a single crystal, whereas the exterior is a polycrystalline aggregate with preferred orientation. These data help to resolve earlier contradictory x-ray and optical evidence.

Trilobite Eyes: Calcified Lenses in vivo

The corneal lenses preserved in the eyes of some of the Paleozoic trilobites (Arthropoda) are constructed of calcite that is crystallographically oriented to behave like glass. The calcareous lenses are capable of forming inverted images over a large depth of field and must have been present in the living trilobites.

Phytochrome in etiolated annual rye: IV. Physical and chemical characterization of phytochrome

Abstract Isolated phytochrome was demonstrated to be free from all but trace impurities by high speed velocity and equilibrium ultracentrifugation, polyacrylamide electrophoresis, and gel filtration in Sephadex G-200. The results from these techniques and from electron microscopy, amino acid analyses, and tryptic peptide separations were consistent with the native phytochrome molecules existing as 14-S hexamers and 9-S tetramers of 2-S monomer units. The monomer unit appears to be chemically identical, existing as a single polypeptide chain of approx. 42 000 molecular weight. These monomer units appear to be associated through noncovalent type bonds. Fluorescence studies indicated that when the 660 nm-absorbing form of phytochrome was excited at 290 nm, it fluoresced intensely at 340 nm and slightly at 672 nm. When excited at 370 nm, it fluoresced at 672 nm.

Eocene Volcanism and the Origin of Horizon A

A series of closely time-equivalent deposits that correlate with seismic reflector horizon A exists along the coast of eastern North America. These sediments of Late-Early to Early-Middle Eocene age contain an authigenic mineral suite indicative of the alteration of volcanic glass. A volcanic origin for these siliceous deposits onshore is consistent with a volcanic origin for the cherts of horizon A offshore.

Precambrian atmospheric oxygen and banded iron formations: A delayed ocean model

Abstract Evidence and arguments increasingly in favor of free oxygen in the Earths early atmosphere renew the constraints on the environmental significance of Precambrian banded iron formations. An early moist greenhouse atmosphere with a delay in, and gradual growth of, the world oceans offers a mechanism to provide a geochemically and mechanically segregated source of iron and silica for banded iron formation, while simultaneously ‘cannibalizing’ evidence for early Archean red beds. The model supports the high rates of weathering necessary to remove initially outgassed CO2 quickly, favors continuity in early biogenic evolution, provides a mechanism for hydrogen and strontium isotope partitioning, and is consistent with iron oxide facies that are devoid of organic carbon or stromatolites that are not encrusted by iron oxide.

Diagenesis of magnesian calcite: Evidence from miliolacean foraminifera

Evidence from Holocene and fossil miliolacean foraminifera indicates that the loss of magnesium from these skeletal magnesian calcites can take place without electron–optically visible alteration in the crystal morphology. A cation exchange reaction is suggested as a possible explanation for this observation. Subsequent stages of textural change (recrystallization) suggest that the loss of magnesium does not necessarily stabilize the resultant calcite from further diagenetic alteration.

Environmental oxygen conditions during the origin and early evolution of life

Abstract The well-known sensitivity of proteins and nucleic acids to UV-radiation requires that some internally consistent protection scenario be envisioned for the origin and early evolution of life on Earth. Although a variety of ozone-surrogates has been proposed, the available biochemical, geochemical and geological evidence best supports the conclusion that free oxygen was available at levels capable of providing at least a moderate ozone screen. Levels of oxygen near 1–2% of the present atmospheric level are consistent with such a screen, and with: (1) the biochemical needs of early procaryotes considered phylogenetically more primitive than the oxygen-producing Cyanobacteria; (2) the rare-earth element data from the oxide facies of the 3.8 Byr-old Isua bandediron formations; (3) the nature and phylogenetic distribution of superoxide dismutases; (4) the need for aerobic recycling of early photosynthetic productivity dictated by the distribution of ancient sedimentary iron and organic carbon; (5) the incompatibility of dissolved reduced sulfur (to support anoxygenic photosynthesis) and ferrous iron (to support banded iron-formations) in the surface waters of the world oceans; and (6) the comparative oxygen and UV-sensitivities of modern procaryotes.

Environmental conditions surrounding the origin and early Archean evolution of life: A hypothesis

Abstract The supposition that free oxygen was absent from the Earths early atmosphere may be questioned. The paradoxes raised for the prebiotic formation of early peptides, proteins and nucleic acids by the absence of oxygen (UV-destruction) and the presence of oceans (spontaneous hydrolysis) are difficult to resolve and are usually ignored. An alternative hypothesis may be entertained that the primitive Earth lacked an early condensed ocean of water and was surrounded instead by a moist greenhouse atmosphere capable of providing the small amounts of photolytic oxygen necessary for a UV-protective ozone screen. These conditions favor the hydration—dehydration cycles needed for complex organic polymerizations, while they minimize the problem of UV-destruction. Simpler prebiotic starting materials can be derived from carbonaceous chondrites (or comets) rather than from terrestrial atmospheric reactions.

Lepidocrocite Iron Mineralization in Keratose Sponge Granules

Reddish-brown granules embedded in the spongin fibers of some keratose sponges consist of very fine crystallites of poorly organized lepidocrocite, γ FeOOH. This is the first occurrence of crystalline iron mineralization in the phylum Porifera and the first indication of hard tissue formation among the Keratosa.