Underlined author denotes designated speaker.
Trees and forests as geoengineers of past and future global climates
1University of Sheffield
For over two decades, it has been widely hypothesized that the origin and diversification of trees and forests accelerated continental silicate weathering, a process regulating atmospheric CO2 over millions of years. I will introduce new evidence supporting this paradigm by illustrating early forest tree rooting systems are linked to enhanced soil weathering processes, as shown by preliminary results from our recent drilling programme in New York State, USA. This raises the question: to what extent can we artificially accelerate the process to sequester our fossil fuel CO2 emissions? Earth system model simulations investigating this issue suggest enhanced weathering through the distribution of pulverised silicate rocks over tropical land could play a significant role in anthropogenic carbon sequestration, with additional benefits of protecting coral reefs from ocean acidification.
Photosynthesis in Proterozoic oceans: evolutionary and ecological innovations
Nicholas J. Butterfield1
1Deparment of Earth Sciences, University of Cambridge
Oxygenic photosynthesis has been driving the global carbon cycle for at least the past three billion years, but the manner in which it has been packaged, and the associated geobiological feedbacks have changed radically over this time. The body-fossil record documents effectively modern cyanobacterial mat biotas in sunlit settings since at least the mid-Palaeoproterozoic, imparting a pervasive sedimentary fabric and accompanying taphonomic signatures. Eukaryotic microfossils are also known from at least the late Palaeoproterozoic, most likely representing benthic photosynthesizers. By the late Mesoproterozoic and early Neoproterozoic these have been joined by a range of unicellular and multicellular plant-protists, though sedimentological and molecular biomarker data point to the continued ecological dominance of cyanobacteria. Eukaryotes were not contributing significantly to ecosystem function until the middle Neoproterozoic, documented by the first quantitative occurrence of eukaryotic steranes. Along with the coincident appearance of testate amoebae and biomineralized scale microfossils, these biomarker data identify a major reorganization of the biological pump – with important implications for interpreting the redox geochemistry and climatic perturbations of the later Neoproterozoic. Full eukaryotic control of marine productivity was achieved during the Ediacaran and Cambrian radiations, establishing the default Phanerozoic condition. The belated shift to a eukaryote-dominated carbon cycle is best explained as a co-evolutionary by-product of early animal evolution.
Distinctive characteristics of flowering plants and their importance
1Department of Earth Sciences, Royal Holloway University of London
(This Abstract will be available online, and on paper at the Meeting.)
Cryptogamic covers and Lilliputian plants in the Mid-Palaeozoic: aspects of early photosynthesising ecosystems on land
Dianne Edwards1 and John A Raven2
2University of Dundee
Cryptogamic covers, terrestrial communities that today colonise soil, rock and even plant surfaces, comprise photosynthesising organisms including cyanobacteria, algae, lichens and bryophytes, plus fungi. Until recently they have received little attention, although, despite their limited extent, it has been estimated that they account for about 7% of carbon dioxide consumed by terrestrial vegetation and, even more remarkably, are responsible for 46% of biological nitrogen fixation on land. It is hypothesised that from mid-Ordovician times until the advent of larger tracheophytes, terrestrial cryptogamic covers contributed to global carbon and nitrogen cycles in similar ways. Fossil evidence will be reviewed including a critical evaluation of that for lichens, and the affinities of very small axial plants (cryptophytes/basal embryophytes), the ecophysiological equivalent of the extant bryophyte component, discussed. Carbon isotope signatures might provide further indirect evidence for the composition of the communities, provided carbon can be obtained from individual plants and carbon inputs from freshwater can be ruled out. These organisms could have increased weathering, producing conditions, including soils, appropriate for subsequent homoiohydric plants and animals. A more quantitative approach is far more contentious because both local and global extents of subaerial colonisation are unknown.
Environmental instability following the rise of oxygenic photosynthesis
1University of Leeds
The evolution of oxygenic photosynthesis irrevocably changed the course of chemical and biological evolution on Earth. Yet, despite this significance, the timing of the evolution of oxygenic photosynthesis is extremely poorly constrained, as are the resultant dynamics and consequences of biospheric oxygenation. Over recent years a wealth of geochemical and geological data has been produced, which in general converges on an environmental signal of oxygenic photosynthesis by at least 2.7 Ga, although more speculative data suggests a much earlier origin. Thus, it appears likely that oxygenic photosynthesis evolved at least several hundred million years before the Great Oxidation Event at ~2.3 Ga. The evolution of oxygenic photosynthesis essentially threw the Earth into a state of turmoil, and it took more than two billion years to achieve the (more or less) stable levels of oxygenation experienced during the Phanerozoic. As well as providing a broad overview of Earth’s oxygenation history, this presentation will include new data that questions both the timing of persistent atmospheric oxygenation, and the concept of an irreversible rise in oxygen after the rise of oxygenic photosynthesis.
The evolutionary history of the phytoplankton
James B. Riding1
1British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
During the Palaeozoic, the principal phytoplankton group was the acritarchs, a polyphyletic group of unknown affinity. They had their origins during the Neoproterozoic and probably represent the resting cysts of extinct unicellular planktonic organisms similar to the dinoflagellates. The acritarchs were abundant and diverse throughout the most of the Early Palaeozoic, but declined markedly during the Carboniferous. Acritarchs were extremely sparse throughout the Carboniferous, Permian and most of the Triassic. During the Triassic, body fossils of dinoflagellate cysts emerged and these diversified significantly during the remainder of the Mesozoic. They declined markedly from the Oligocene, probably in response to falling global temperatures and sea levels. The dinoflagellates underwent a significant evolutionary radiation during the latest Early Bajocian (~ 169 Ma), and this event is coincident with diversifications and radiations in other fossil groups. For example the closely-related calcareous nannofossils diversified, and planktonic foraminifera are observed for the first time. This Bajocian radiation of dinoflagellates is a significant watershed and represents the dawn of modern planktonic biotas. The precise reasons behind this evolutionary event are not known with certainty; it may be related to the breakup of Panagea and related changes in global palaeoceanography, and/or the Mesozoic Marine Revolution.
Cyanobacteria and the Great Oxidation Event: Evidence from genes and fossils
*Bettina E. Schirrmeister1
1School of Earth Sciences, University of Bristol
Cyanobacteria are among the oldest organism on this planet and unique among prokaryotes, regarding their age, morphology and fossil record. Their ability to gain energy via oxygenic photosynthesis transformed Earth’s atmosphere and redefined the evolutionary boundaries of life. More than 2.4 Ga they caused one of the most dramatic environmental changes in the the history of our planet, the ’Great Oxidation Event’ (GOE). Yet, the origin of cyanobacteria and their morphological disparity, as well as, their causal association to the rapid accumulation of atmospheric oxygen are not resolved. Previous phylogenetic studies I have conducted suggest that the origin of multicellular cyanobacteria might be associated with the GOE.
In the fossil record unequivocal cyanobacterial fossils are not found before 2.Ga. Fossil findings from the Archean and early Proterozoic failed to provide enough taxonomic information using traditional methods. To resolve the occurrence of multicellular cyanobacteria during the early Precambrian, I have combined novel data on morphotype disparity and abundance from Synchrotron Radiation X-ray tomographic microscopy, with phylogenetic analyses of all major prokaryotic taxa. Resuts suggest that multicellular fossils from the Archean/early Proterozoic can only be compared to modern Cyanobacteria, Chloroflexi or Actinobacteria among the Eubacteria.
Evidence for terrestrial photosynthetic organisms in the Proterozoic: the land becomes vegetated
Charles H. Wellman1
1Dept. of Animal & Plant Sciences, University of Sheffield
Pre-Ordovician terrestrial deposits are rare and are both difficult to recognize and age constrain. Nevertheless recent work on billion year old terrestrial deposits of the Torridonian of Scotland and the Nonesuch Shale of Michigan, USA is demonstrating the existence of diverse freshwater aquatic and terrestrial biotas. These biotas include cyanobacteria and primitive eukaryotes, with a number of basal protist groups, such as euglenids, identified. Interestingly, emerging evidence from phylogenetic analyses, molecular clock studies and ancestral state reconstruction suggests that freshwater and terrestrial environments may have been much more important than previously anticipated in the evolution and diversification of life on Earth. Cyanobacteria have been shown to be an essentially non-marine group that most likely originated in freshwater environments where they diversified. Ultimately they were integral to the origin of photosynthetic eukaryotes having given rise to the chloroplast. All of these events may have occurred in non-marine environments, away for the ‘poisonous’ anoxic/euxinic oceans. We often think of carbon cycling on Proterozoic Earth as being driven by the marine carbon-cycle. Also important was the terrestrial carbon-cycle, dominated by aquatic/terrestrial photosynthesis and carbon burial, combined with silicate rock weathering by microbial soil crusts during development of rudimentary soils.