In the billions of years since simple unicellular life sprang forth from the depths of Earth’s oceans, life has blossomed into so much variety and form that it almost seems skeptical to think that all life alive today at some point shared a single ancestor—the Last Universal Common Ancestor (LUCA).
Many studies have since tried to give us even just a glimpse into what LUCA may be like. LUCA may very well be a unicellular organism, too, given how most primitive life-forms on Earth looked like. It might also have some DNA locked inside its body somewhere, which would be shaped like a ring. Beyond those details, though, things get real blurry.
In a similar vein, scientists are also hard at work looking for what factors may have affected such an explosion of variety in the species that crawl, walk, swim, and fly across and through our planet. One such effort is a recent study published in the Proceedings of the National Academy of Sciences, whose research team was led by Jon Wade from the University of Oxford.
Wade and team were in pursuit of the role of iron (Fe) in the evolution of complex life on our planet. Iron, as we all know, is pretty abundant on Earth’s surface, and this team of researchers think that it may have played a more active role in the trajectory taken by Earth’s organisms than previously thought. We have iron in our bodies ourselves; it’s what allows us to replicate DNA and sense our oxygen levels.
Wade and team produced some insights from whatever data they managed to gather. As it turns out, back in the very early days, iron was in abundance around the Earth. These surface iron deposits were left behind by meteorites as parting gifts, and were left to dissolve into the first oceans on Earth. From there, the earliest organisms incorporated iron into their bodies.
However, the onset of the Great Oxidation Event (GOE) suddenly granted the planet with an excess of oxygen (O); the soluble iron that was once prevalent in the oceans were suddenly consumed as they were oxidized by the oxygen, leaving organisms with iron oxides that they had no means of utilizing. This meant that whatever iron that was left lying around was suddenly all the more precious—and some of them were locked within fellow unicellular organisms.
Thus, organisms devised new ways of harvesting iron from fellow organisms, whether alive or dead. They now had to learn ways of gathering iron from other cells—either by stealing them from both dead and living cells, as well as staying put inside another living cell and simply subsisting on whatever mechanism their host cell used to gather iron. Thus, according to Wade and team, the sudden depletion of free iron in the environment is what drove forwards the evolution of multicellular organisms.
“Life had to find new ways to obtain the iron it needs,” said co-author and Oxford Professor of Iron Biology Hal Drakesmith. “For example, infection, symbiosis and multicellularity are behaviours that enable life to more efficiently capture and utilise 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.”
And, according to what they had found, the implications of what role iron may have played on our planet might give us valuable insights into what role it similarly plays for life on other planets.
“It is not known how common intelligent life is in the Universe,” Drakesmith followed. “Our concepts imply that the conditions to support the initiation of simple life-forms are not enough to also ensure 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 be low.”
References
- Cassella, C. (2021, December 7). This element could have been crucial to the evolution of complex life on earth. ScienceAlert. https://www.sciencealert.com/this-one-element-could-have-been-crucial-to-evolution-of-complex-life-on-earth
- University of Oxford. (2021, December 6). Iron integral to the development of life on Earth – and the possibility of life on other planets. EurekAlert! https://www.eurekalert.org/news-releases/936976
- Wade, J., Byrne, D. J., Ballentine, C. J., & Drakesmith, H. (2021). Temporal variation of planetary iron as a driver of evolution. Proceedings of the National Academy of Sciences, 118(51). https://doi.org/10.1073/pnas.2109865118
