Oxygen is a vital part of life. Multicellular life on our planet began to thrive after a surge in this gas in the atmosphere 2.5 billion years ago.
Oxygen can't take all the credit for the timing. Some scientists claim that there is another element that is crucial to the evolutionary boom, and it's called iron.
Jon Wade and his team at the University of Oxford propose that iron's fluctuations helped to drive evolution on Earth.
Iron is an essential element in almost all life. It allows cells to sense oxygen, generate energy, and express genes. There are only two known organisms that do not need this metal to survive.
There was a lot of geological iron in the early days of Earth. The iron found here was probably created by meteorites from outer space, and it was abundant in the marine environment.
Conditions began to change after the GOE. Competition for iron among cells increased assoluble iron began to grow scarce.
Life-forms had to figure out how to recycle iron from dead cells, steal iron from live cells, or live in another cell to stay alive.
Some scientists believe the first multicellular evolution was triggered by iron battles.
The authors say that all of the three behaviors that switch the focus of iron acquisition from mineral sources to other life-forms may evolve into the others over time.
Older forms of single-celled life, likebacteria and Archaea, are thought to have relied more on iron to survive.
Modern organisms have learned to use the element more efficiently as the environment has changed.
The oceans lost most of their iron because of the increase in atmospheric oxygen.
Cells need to evolve siderophores to grab the element in this form. Billions of years ago, this was a new form of survival and is still present today.
Researchers think crowding inevitably led to complex cell-cell interactions as life-forms with siderophores began to gather near a limited number of iron-rich geological sources.
Modern eukaryotes can live outside of geological sources if there are biological forms of iron available.
Iron has retained its preeminence in biological systems despite the fact that it was no longer available after the GOE.
It's possible that iron has unique electrochemical properties that make it possible, or make efficient, a range of biochemical processes, such that other elements cannot be broadly substituted for iron within the proteins, without causing a significant disadvantage.
The lack of iron means organisms had to compete, cheat, or cooperate to survive, and these developments could have caused extreme adaptation in genomes and cellular behavior over time.
About 500 million years ago, the Neoproterozoic Oxygenation event made the changes worse.
When iron became scarce, life-forms began to grow in complexity.
Researchers say we need to know more about how life copes with the ebbs and flows of iron deficiency, given that a rise in atmospheric CO2 could increase it.
The findings show that iron oxide can be found in the mantle of Mars, which could be used to measure the potential for life on other planets. If the planet is rich in iron, it could indicate a harbor for some of the simplest forms of life.
The research was published in a journal.
