A Multidisciplinary Investigation on the Influence of Archean Seawater Composition and UV radiation levels on the Survival and Evolution of Early Microorganisms

• Author / Creator

  Mloszewski, Aleksandra M.

• Life evolved in the oceans nearly four billion years ago, but the environmental conditions surrounding its evolution remains poorly understood. While Archean seawater (2.5 to 3.8 Ga) provided ancient microorganisms with the bioactive trace metals needed to sustain their metabolic requirements, it also presented high levels of UV radiation and toxic iron levels that made early marine environments inhospitable to life. Nevertheless, the existence of Archean-aged fossil evidence suggests that early microorganisms overcame these challenges and thrived in ancient shallow marine communities. The answer to how they achieved this lies in the composition of Archean seawater. Using the composition of banded iron formations (BIF) from the recently discovered ≥3.75 Ga Nuvvuagittuq Supracrustal Belt and the ≥3.77 Ga Nulliak Supracrustal Association as proxies for Eoarchean seawater composition, we show that the early oceans were rich in Ni and Zn. In methanogens (methane-producing bacteria), Ni is a key metal co-factor in the enzymes responsible for methane production. High Ni abundances in Eoarchean seawater facilitated the proliferation of large communtities of methanogens, which were responsible for much of the methane production in the early atmosphere. In terms of Zn, the relatively late appearance of Zn enzymes in eukaryotes has been previously linked to biolimiting marine Zn abundances in the Archean oceans. Instead, this study shows that Zn only varied within an order of magnitude of modern levels. These new observations decouple the relatively late appearance of eukaryotes from the geochemical evolution of Zn in ancient seawater. Much as the rise of oxygen was important to the proliferation of eukaryotes, this study also demonstrates that high concentrations of iron and silica may have been instrumental to the initial survival of the most ancient planktonic bacteria, as well as to the early colonization of littoral marine environments. High UV radiation levels are detrimental to living organisms by causing lesions on DNA molecules, producing critical errors during the transcription of genetic material. Furthermore, the high iron concentrations present in Archean seawater were toxic to cells, through the production of reactive oxygen species (ROS). The intracellular accumulation of ROS has significant metabolic consequences, such as damage to genetic material (DNA and RNA), as well as protein deterioration and lipid peroxidation, any of which can lead to cell death. Silica played an important protective role for ancient planktonic bacteria by complexing with the iron in Archean seawater. The effects of this reaction were twofold: it lowered the level of soluble, bioavailable iron to more biologically manageable levels, enabling the survival and evolution of early bacteria under high iron conditions. Soluble iron is known for its efficiency at absorbing UV radiation. Aqueous silica delays the precipitation of ferric oxyhydroxide minerals through the formation of nanometer-sized iron-silica colloids. By keeping iron suspended in the water column in this way, silica maintained the role of iron as an effective UV shield. Thus protected from conditions that would otherwise be detrimental to life, early microorganisms were able to thrive in Archean marine habitats. By applying information from the Archean rock record to geochemical and biological models, this multidisciplinary approach has allowed the elucidation of a number of important interactions between the hydro-, litho- and atmosphere and early life.

• Subjects / Keywords

  • Archean
  • UV radiation
  • Seawater composition

• Graduation date

  Fall 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R31J97G9M

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.