Land plants at the P-Tr boundary

The Permian to Triassic transition involved a transformation from globally cool conditions to a hothouse, as well as the largest mass extinction in the fossil record.  It also spanned a time when most continental lithosphere was clumped in the Pangaea supercontinent.  In the case of plants, it is not easy to sort the effects of climatic shifts from those due to catastrophic events, either the effects of the huge Siberian flood-basalt event (see Earth Pages August 2002, Flood basalts of Siberian Traps doubled at a stroke) or a yet to be proven impact.  Allister Rees of the University of Chicago has painstakingly organised global Permian and Triassic floral data to see if the changes were slow (climatically influenced) or sudden ( possible evidence for a catastrophic collapse),a nd if they coincide from region to region.  He found that in some regions big changes happened quickly around the P-Tr boundary, but in others the shifts were protracted and unrelated to faunal extinctions (Rees, P. McA. 2002.  Land-plant diversity and the end-Permian mass extinction.  Geology, v. 30, p. 827-830).  This clearly implies caution in the interpretation of detailed local records as signs of massive events, and also points out the need to place such records in the contexts of global climate belts and biases that result from varied degrees of biotic preservation.

Dinosaurs did urinate

News is coming in (New Scientist, 19 October 2002, p. 26) of a startling find along a dinosaur trackway in Colorado.  At the October meeting of the Society of Vertebrate Palaeontology, Katherine McCarville of the South Dakota School of Mines and Technology described a bath-sized pit preserved among sauropod footprints.  Seemingly, all the evidence points to it having been excavated by a gargantuan stream of liquid pouring from above.  Ranking as a candidate for the IgNobel Awards of 2003, this evidence for dinosaurian bladder relief may shake the theory that birds are descended from dinosaur ancestors; birds do not urinate.

Continents colonised a billion years ago

The Torridonian of NW Scotland is a thick sequence of mainly terrestrial sediments that accumulated on the Laurentian craton, between 1200 and 1000 Ma ago.  Much of the sequence evidences braided-stream deposition, with brief lacustrine episodes.  Any geologist who examines these mainly siliciclastic rocks will find abundant evidence for subaerial conditions in the form of desiccation cracks, often affecting directional current ripples.  However, it takes a keen eye and some knowledge of biofilms to spot any signs of microbial activity.  In sandstones they manifest themselves by having increased the normally very low cohesiveness of wet sand by their binding action (Prave, A.R. 2002.  Life on land in the Proterozoic: evidence from the Torridonian rocks of northwest Scotland.  Geology, v.  30, p. 811-814).  Prave analysed the shapes of desiccation polygons to show that the Torridonian sands were unusually cohesive, and recognised other features likely to have been formed by microbial crusts.  These finds add to the growing evidence for substantial terrestrial biomass, long before the “official” colonisation by land plants in the Silurian and Devonian.  Whether or not such an expansion of the biosphere added significantly to carbon burial and drawdown of atmospheric CO2, as it did in post-Silurian times, remains to be determined from average carbon contents of quite rare Precambrian terrestrial sediments,


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