50 research outputs found
True substrates: The exceptional resolution and unexceptional preservation of deep time snapshots on bedding surfaces
Abstract: Rock outcrops of the sedimentaryâstratigraphic record often reveal bedding planes that can be considered to be true substrates: preserved surfaces that demonstrably existed at the sedimentâwater or sedimentâair interface at the time of deposition. These surfaces have high value as repositories of palaeoenvironmental information, revealing fossilized snapshots of microscale topography from deep time. Some true substrates are notable for their sedimentary, palaeontological and ichnological signatures that provide windows into key intervals of Earth history, but countless others occur routinely throughout the sedimentaryâstratigraphic record. They frequently reveal patterns that are strikingly familiar from modern sedimentary environments, such as ripple marks, animal trackways, raindrop impressions or mudcracks: all phenomena that are apparently ephemeral in modern settings, and which form on recognizably human timescales. This paper sets out to explain why these shortâterm, transient, smallâscale features are counterâintuitively abundant within a 3.8 billion yearâlong sedimentaryâstratigraphic record that is known to be inherently timeâincomplete. True substrates are fundamentally related to a state of stasis in ancient sedimentation systems, and distinguishable from other types of bedding surfaces that formed from a dominance of states of deposition or erosion. Stasis is shown to play a key role in both their formation and preservation, rendering them faithful and valuable archives of palaeoenvironmental and temporal information. Further, the intersection between the timeâlength scale of their formative processes and outcrop expressions can be used to explain why they are so frequently encountered in outcrop investigations. Explaining true substrates as inevitable and unexceptional byâproducts of the accrual of the sedimentaryâstratigraphic record should shift perspectives on what can be understood about Earth history from field studies of the sedimentaryâstratigraphic record. They should be recognized as providing highâdefinition information about the mundane day to day operation of ancient environments, and critically assuage the argument that the incomplete sedimentaryâstratigraphic record is unrepresentative of the geological past
Genetic and antigenic analysis of Babesia bigemina isolates from five geographical regions of Brazil
The influence of surface energy on the wetting behaviour of the spore adhesive of the marine alga Ulva linza (synonym Enteromorpha linza)
The environmental scanning electron microscope has been used to image the adhesive pads secreted by zoospores of the marine alga Ulva linza as they settle on a range of self-assembled and grafted monolayers of different wettability, under natural, hydrated conditions. Results reveal that the diameter of the adhesive pad is strongly influenced by surface wettability, the adhesive spreading more (i.e. wetting the surface better) on the more hydrophilic surfaces. This is in direct contrast to previous observations on the spreading of marine bioadhesives and is in apparent contradiction to the predictions of the YoungâDupre equation for three-phase systems. In this paper, we attempt an explanation based upon thermodynamic analysis of the wetting properties of hydrophilic proteins