As biogeochemists, we are obsessed (!) with the journey of elements from the earth’s crust through the ocean and ultimately to feed life throughout Earth’s history. Life has evolved to use the chemical ingredients most easily found i.e. those in high abundance in the ocean and with unique and useful chemical properties.
The chemistry of the ocean is not simply related to the chemistry of Earth’s crust: elements are mobilised according to their solubility under the environmental conditions of the time. As a result, the availability of elements in the ocean has changed drastically through Earth's history and particularly upon oxygenation of the atmosphere by proliferating photosynthesisers.
Of note, iron became insoluble, as iron oxy-hydroxides (in effect, the planet “rusted”), and Cu and Zn were released from insoluble sulphide phases. This oxygenation of the planet occurred in parallel with the advancement in complexity of cells from relatively simple bacteria to compartmentalised cells of the eukaryote - that organised their DNA in the nucleus - and ultimately multicellular organisms, raising the possibility that changing seawater chemistry paced evolution (Cu and Zn both perform distinct roles unique to multicellularity).
The changing availability of the metals in the ocean is reflected in the chemistry of these more complex organisms compared with more primitive forms, with lower Fe, but high Cu and Zn requirements. The chemical requirements of different forms of life act as a fossil representation of ancient seawater chemistry.
Oxford OceanBug Research
We have recently published a paper detailing our discovery that a living form of archaea which evolved originally over 2 billion years ago has the highest need for iron of any marine plankton. This was driven by its evolution in an ancient environment where iron was much more readily available than in our surface ocean today.
Read more about our research here: