Literature Review: The Early Earth

by Carl Strang

This week’s literature review begins a 4-week series that updates the material I shared in the Prehistoric Life winter series a couple years ago. The studies highlighted below looked at the time period from the Earth’s origin through the Paleozoic Era.

M. Touboul, I. S. Puchtel, R. J. Walker. 182W Evidence for Long-Term Preservation of Early Mantle Differentiation Products. Science, 2012; DOI: 10.1126/science.1216351

As described in a ScienceDaily article. They found evidence, in the form of a high portion of a particular tungsten isotope in some volcanic rocks, that a portion of the Earth’s previously formed mantle survived the Theia impact intact, implying that the Earth did not completely melt during or after that event. (This was the collision that in one dramatic moment created our moon and tilted the Earth on its axis, so that the seasons and the tides, so important to the diversity of life on Earth, became possible.)


Alexander, C.M.O’D., et al. 2012. The provenances of asteroids, and their contributions to the volatile inventories of the terrestrial planets. Science 337:721-723.

They looked at isotopic ratios of elements in asteroids vs. comets, and concluded that most of the water, nitrogen and carbon in the Earth and other inner planets came from bombardment by meteorites that originated as asteroids, rather than from comets.


M. R. Smith. Mouthparts of the Burgess Shale fossils Odontogriphus and Wiwaxia: implications for the ancestral molluscan radula. Proceedings of the Royal Society B: Biological Sciences, 2012; DOI: 10.1098/rspb.2012.1577

As reported in a ScienceDaily article. Graduate student Martin Smith examined fossils with a new form of electron microscopy, and found mouthparts that are clear predecessors of the molluscan radula. That early, tonguelike feature likely was used for scooping food from muddy sea floors rather than for scraping as radulas do today.

The following study points to green algae as the ancestors of all the land plants.

The following study points to green algae as the ancestors of all the land plants.

Timme RE, Bachvaroff TR, Delwiche CF (2012) Broad Phylogenomic Sampling and the Sister Lineage of Land Plants. PLoS ONE 7(1): e29696. doi:10.1371/journal.pone.0029696

They constructed a comparison of 160 nuclear genes to identify which group of algae contains the ancestral species which invaded land and became the founding species from which all land plants evolved. Their results point to the Zygnematales, the pond scum algae group.


Timothy M. Lenton, Michael Crouch, Martin Johnson, Nuno Pires & Liam Dolan. First plants cooled the Ordovician. Nature Geoscience, 2012 DOI: 10.1038/ngeo1390

From ScienceDaily. Their experiments on the chemical weathering of rocks by mosses suggest that the invasion of land plants released minerals that took carbon dioxide out of the atmosphere, and also stimulated oceanic blooms that further sequestered carbon as the resulting organisms were buried, in addition to the carbon sequestered by the land plants themselves. The authors estimate that the resulting carbon dioxide depletion was sufficient to trigger the end-Ordovician ice ages and associated extinctions. They also point out that plants continue to have a cooling effect on the atmosphere, though in the present day this is overwhelmed by technological injection of carbon dioxide.

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