Iron is an essential nutrient for life. The initial development of Life on Earth is also linked to iron. The amount of iron in the Earth’s rocky mantle was ‘set’ by the conditions under which the planet formed and went on to have significant ramifications for how life developed.
A new study by the University of Oxford has shed light on the importance of iron for the development of complex life on Earth. This study could answer how likely (or unlikely) advanced life forms might be on other planets.
Scientists uncovered the possible mechanisms by which iron influenced the development of complex life forms.
Co-author Jon Wade, Associate Professor of Planetary Materials at the Department of Earth Sciences, University of Oxford, said, “The initial amount of iron in Earth’s rocks is ‘set’ by the conditions of planetary accretion, during which the Earth’s metallic core segregated from its rocky mantle. Too little iron in the rocky portion of the planet, like Mercury, and life is unlikely. Too much, like Mars, and water may be difficult to keep on the surface for times relevant to the evolution of complex life.”
Initially, iron conditions on Earth were considered optimal for maintaining surface retention of water. However, the Great Oxygenation Event causes oxygen levels to rise on Earth. This increase in oxygen causes a reaction with iron, which leads to it becoming insoluble. Gigatons of iron dropped out of seawater, which was much less available to developing life forms.
Co-author Hal Drakesmith, Professor of Iron Biology at the MRC Weatherall Institute of Molecular Medicine, University of Oxford, said, “Life had to find new ways to obtain the iron it needs. For example, infection, symbiosis, and multicellularity are behaviors that enable life to more efficiently capture and utilize this scarce but vital nutrient. Adopting such characteristics would have propelled early life forms to become ever more complex, on the way to evolving into what we see around us today.”
The requirement for iron as a driver for evolution, and the subsequent development of a complex organism capable of acquiring poorly available iron, may be rare or random occurrences. This has implications for how likely complex life forms might be on other planets.
Prof Drakesmith said, “It is not known how common intelligent life is in the Universe. Our concepts imply that the conditions to support the initiation of simple life-forms are not enough to ensure the subsequent evolution of complex life-forms. Further selection by severe environmental changes may be needed – for example, how Life on Earth needed to find a new way to access iron. Such temporal changes at planetary scale may be rare, or random, meaning that the likelihood of intelligent life may also below.”
“However, knowing now about how important iron is in the development of life may aid in the search for suitable planets that could develop life forms. By assessing the amount of iron in the mantle of exo-planets, it may now be possible to narrow the search for exo-planets capable of supporting life.”
- Jon Wade et al. Temporal variation of planetary iron as a driver of evolution. DOI: 10.1073/pnas.2109865118