First plants cooled the Ordovician

Journal name:
Nature Geoscience
Volume:
5,
Pages:
86–89
Year published:
DOI:
doi:10.1038/ngeo1390
Published online

The Late Ordovician period, ending 444 million years ago, was marked by the onset of glaciations. The expansion of non-vascular land plants accelerated chemical weathering and may have drawn down enough atmospheric carbon dioxide to trigger the growth of ice sheets.

At a glance

Figures

  1. Global changes during the Ordovician period.
    Figure 1: Global changes during the Ordovician period.

    Appearances of non-vascular18 and vascular23 plants dot the timeline of climate change as recorded by conodont δ18O values1 (diamonds, left-hand scale). The appearance of non-vascular plants is followed by an increase in the abundance and weathering of volcanic rock, as recorded by seawater 87Sr/86Sr (ref. 11). The weathering seems to coincide with a drop in atmospheric CO2 concentrations (solid squares, outer right-hand scale), though proxy-based estimates are scarce and highly uncertain5, 6, 7. Glacial deposits appear early in the Late Ordovician and increase in frequency as it progresses13, and phosphate deposits appear then in marine settings14. Two carbon isotope excursions also mark the Late Ordovician: the Guttenberg and Hirnantian isotopic carbon excursions (GICE and HICE)13. T., Tremadogian age; H., Hirnantian age.

  2. Moss enhances the weathering of Al, Ca, Fe, K and Mg from silicates.
    Figure 2: Moss enhances the weathering of Al, Ca, Fe, K and Mg from silicates.

    Summary of results from all weathering experiments on different substrates: a, granite (control n = 77; moss n = 72) and b, andesite (control n = 37; moss n = 41). The amount weathered in micromoles (mean of all microcosms of each substrate) are shown, with abiotic and total biotic (moss + water) data in separate columns. The weathering 'amplification factor' due to the presence of moss = total biotic weathering/abiotic weathering. Error bars represent ~95% confidence intervals applied using the Student's t-test.

  3. Model results.
    Figure 3: Model results.

    Predicted Ordovician variations in a, atmospheric CO2, b, global temperature, and c, δ13C of marine carbonates, for: baseline model with Ordovician geological forcing and changing solar luminosity only (red dotted line), including enhancement of silicate weathering by non-vascular plants (blue dashed line), and adding transient enhancement of phosphorus weathering by early plants (green solid line).

References

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Author information

Affiliations

  1. College of Life and Environmental Sciences, University of Exeter, Hatherly Laboratories, Prince of Wales Road, Exeter, EX4 4PS, UK

    • Timothy M. Lenton
  2. Earth and Life Systems Alliance, School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK

    • Timothy M. Lenton,
    • Michael Crouch &
    • Martin Johnson
  3. Earth and Life Systems Alliance, Department of Cell and Developmental Biology, John Innes Centre, Norwich, NR4 7UH, UK

    • Michael Crouch,
    • Nuno Pires &
    • Liam Dolan
  4. Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK

    • Nuno Pires &
    • Liam Dolan

Contributions

T.M.L. and L.D. designed the study. M.C. conducted the microcosm experiments with input from N.P. and L.D. M.C., M.J., L.D. and T.M.L. conducted geochemical analyses. N.P. and L.D. identified acids in moss exudates. T.M.L. did the modelling and sensitivity analyses. T.M.L. and L.D. wrote the paper with input from M.J., M.C. and N.P.

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The authors declare no competing financial interests.

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    First plants cooled the Ordovician

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