Aerobic respiration in the Archaean?

The Earth's atmosphere during the Archaean era (3,800-2,500 Myr ago) is generally thought to have been anoxic, with the partial pressure of atmospheric oxygen about 10(-12) times the present value. In the absence of aerobic consumption of oxygen produced by photosynthesis in the ocean, the major sink for this oxygen would have been oxidation of dissolved Fe(II). Atmospheric oxygen would also be removed by the oxidation of biogenic methane.

Structural distinction between ferritin and iron-dextran (imferon). An electron diffraction comparison.

Electron diffraction data from ferritin, iron-dextran (Imferon), ferrihydrite, and beta-FeOOH support earlier suggestions that ferritin iron and ferrihydrite are structurally the same and totally different from Imferon and beta-FeOOH, which are closely related. The conclusion that ferritin and Imferon are uniquely similar is not confirmed. Ferrihydrite-dextran complexes should make a better analog than existing iron-dextrans for the study of ferritin iron-protein interactions.

Tentaculites: evidence for a brachiopod affinity?

Transmission electron microscope studies of fractured surfaces reveal that the shells of Tentaculites are constructed of calcite with a ridge and groove structure and cross-bladed fabric heretofore unique to some articulate brachiopods. A possible affinity with brachiopods or phoronids is suggested for Tentaculites.

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.

Montmorillonite: electron diffraction from two-dimensional single crystals.

Some Selected area electron diffraction patterns of isolated monocrystalline particles of both Wyoming and Camp Berteaux sodiumti-monfmorillonites fail to show the mirror platne symmetry required for the accepted structure. A triclinic model deserves consideraction.

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.

Oxygen-collagen priority and the early metazoan fossil record.

The thesis is developed that a low oxygen level Precambrian atmosphere presented early-evolving metazoan organisms with physiological connective tissue priorities resulting from the important molecular oxygen requirements in the biosynthesis of collagen hydroxyproline. Shells, cuticles, and carapaces which are not mandatory metazoan prerequisites but which directly or indirectly demand substantial connective tissue collagen are oxygen expensive, low priority features. A marked increase in atmospheric oxygen level near the beginning of the Paleozoic would eliminate oxygen-collagen priorities simultaneously and on a world-wide basis in all metazoan stocks providing evolutionary pressure for enlarged musculatures and associated "hard parts.