Iron is an essential nutrient that almost all life requires to grow and thrive. Iron’s importance goes all the way back to the formation of the planet Earth, where 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 major ramifications for how life developed. Now, scientists at the University of Oxford have uncovered the likely mechanisms by which iron influenced the development of complex life forms, which can also be used to understand how likely (or unlikely) advanced life forms might be on other planets. The work was published recently in PNAS.
“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,” says co-author Jon Wade, Associate Professor of Planetary Materials at the Department of Earth Sciences, University of Oxford. “Too little iron in the rocky portion of the planet, like the planet 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 would have been optimal to ensure surface retention of water. Iron would have also been soluble in sea water, making it easily available to give simple life forms a jumpstart in development. However, oxygen levels on Earth began to rise approximately 2.4 billion years ago. An increase in oxygen created a reaction with iron, which led to it becoming insoluble. Gigatons of iron dropped out of sea water, where it was much less available to developing life forms.
The need for iron as a driver for evolution, and consequent 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.
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.
For more information: Proceedings of the National Academy of Sciences (PNAS)
