Fig leaves over Palaeocene-Eocene boundary

Methane-induced warming around 55 Ma ago was one of the greatest environmental upheavals of recent geological time. Pretty quickly, all the methane belched out by destabilisation of sea floor gas hydrates would have forced up atmospheric CO concentrations.  The estimated climatic effect was astonishing: a global temperature rise of the order of 5-10°C in 10-20 thousand years. The early Eocene world would have become a steamy place, and the changes certainly tally with shifts in a range of faunas, from foraminifera to large mammals. Not many people have reported any coincident changes in plant fossils, even though a moist atmosphere charged with CO2 would have encouraged growth enormously. A reflection of the changed conditions does come from rapidly changing leaf shapes and sizes, however. One of the key sections that does reveal floral change is in terrestrial sediments preserved in the Bighorn Basin of Wyoming, USA (Wing, S.L. et al. 2005. Transient floral change and rapid global warming at the Paleoene-Eocene boundary. Science, v. 310, p. 993-996). Tied down from a dramatic change in carbon isotopes, the boundary section not only shows the rapid dominance of leaves with extended ‘drip tips’ that allow rainwater to be shed quickly, but an influx of genera unknown from the Palaeocene below.  The invasive groups are known from sediments of that age from much further south in the US, and even from Europe at the other side of the opening Atlantic Ocean. So it seems that there was a rapid northward plant colonisation over 4 to 20 degrees of latitude. The section perhaps gives a flavour of floral changes that might occur should modern anthropgenic warming go unchecked.

Dinosaur dung, the Deccan Trap and grass

Yes, it has to come to a pretty pass when geologists will tramp to the very base of the Deccan continental flood basalts, dig up and then finger through dinosaur crap. The temptation of a bed consisting of little other than coprolites  deposited by sauropods, especially beneath the very lavas implicated by some in their demise, is huge. It isn’t the first time that coprophilia has struck the vertebrate palaeontological community, for a very good reason: if dinosaurs grew so darned big what did they eat? That it included grass is a surprise for palaeobotanists, but would have been a great treat for the thunder lizard, for there is nothing more toothsome to a herbivore than a hay snack; much better than a monkey puzzle leaf. Indian and Swedish geologists hit the headlines with their discovery (Prasad, V. et al. 2005. Dinosaur coprolites and the early evolution of grasses and grazers. Science, v. 310, p. 1177-1180). The lithified dung contains unmistakable traces of silica-rich phytoliths that occur only in grasses. Some possible grass pollen has been found before in Late Cretaceous sediments, but the crown-group Poaceae, that still thrive today, had been thought to have appeared later than the Early Eocene. It now seems likely that grasses appeared first in Gondwana, being transferred to Eurasia by the collision of its wandering fragment India around 50 Ma ago – India had already begun to move independently at the time of Deccan eruptions. Genetic studies of grasses points to their origin about 80 Ma ago, so it is likely that those in the dung are among the earliest. The Indian titanosaurs that ate them were not grazers, however, because the dung is also full of remains of conifers, palms and other vegetation that would have been abundant in those times. Interestingly, mammals from palaeosols within the Deccan lava sequence have cheek teeth reminiscent of the dominant grazers of later time.

Clay minerals and the origin of life

J.D. Bernal, a former student of J.B.S. Haldane, had as wide a range of interests as his mentor. Though a member of the Communist Party of Great Britain at the height of its loyalty to Stalin, during World War II he was a scientific advisor to Churchill. Among his many contributions was an idea inspired by Haldane’s conviction that life emerged from the inorganic world through simple chemical processes. Bernal thought in terms of a template sufficiently complex to shape early organic molecules, and clay minerals fitted that particular bill because they contain loosely bonded, yet complex passageways between the sheets of linked SiO4 tetrahedra that form the bulk of their structure. A group of geochemists from Arizona State University have experimented on the organic catalytic potential of clays by simulating conditions around sea-floor vents that may have been the haven in which terrestrial life first formed (Williams, L.B. et al. 2005. Organic molecules formed in a ‘primordial womb’. Geology, v. 33, p. 913-916). Their ‘feedstock’ was dilute methanol and the clays that they chose were montmorillonite, illite and saponite, the last a member of the smectite group with high magnesium that forms by hydrothermal alteration of olivine and pyroxene in basalts. More complex hydrocarbons, with up to 20 carbon atoms per molecule, did indeed form in their experiments. The results suggest that smectite clays protect such unstable hydrocarbons from thermal decay, but no distinct life-forming molecules, such as amino acids, showed up. The products were polycyclic aromatic hydrocarbons, but it is possible that they would have formed a diverse feedstock for other processes once the hydrothermal clays were deposited in cooler conditions.


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