How fragile is life on Earth? A rock from an iron ore mine housed in Museum Victoria gives us a clue. It’s a visual reminder of the instability that happens when we remove wildlife. In the long-distant past Earth couldn’t have supported humans. It’s only the rich abundance of animals today that stops wild fluctuations in our climate and planetary life support systems. Life on Mars, for instance, never made it through this stage.
Oxygen giveth and taketh away
Oxygenation of Earth’s atmosphere began about 2.5 billion years ago. Up until about 1.8 billion years ago Earth underwent a period of huge turbulence. So, as Earth grew accustomed to the demands of newly-evolved microorganisms, there were alternating periods dominated by oxygen and iron. Both the aforementioned elements can be used to fuel life. But it would be many more billions of years before oxygen-dependent animals took over the land.
In this early time our seas were dominated by types of primitive bacteria. They were the first wildlife able to start making oxygen.
Oxygen is the main by-product of photosynthesisMeaning how plants extract energy by absorbing water and using radiation from the Sun to combine it with carbon dioxide to create sugars. More. It’s a relatively simple equation that uses sunlight to turn carbon dioxide and water into fuel (sugars) and oxygen.
Ironically oxygen happens to be toxic to life forms. So, this is why our lives are so finely balanced with the ecosystemsHow ecosystems function An ecosystem is a community of lifeforms that interact in such an optimal way that how ecosystems function best, is when all components (including humans and other animals) can persist and live alongside each other for the longest time possible. Ecosystems are fuelled by the energy created by plants (primary producers) that convert the Sun's heat energy More (and animals) around us.
Humans can’t tolerate more than a slight increase or decrease in atmospheric concentration of oxygen. Divers commonly use oxygen-enriched air to limit their nitrogen saturation. But at depths, more than about 30m, will risk central nervous system impacts.
Alternating oxygen and iron states
As cyanobacteriaAn early form of life that still exist today and are super-abundant in our oceans. They are similar to bacteria and are not algae but are capable of photosynthesis. More flourished along with purple bacteria, they depleted the ocean’s iron reserves. Until now these had been cleaning the sea of toxic oxygen. How this works is that iron bonds with oxygen to create ‘rust’ and falls to the seafloor.
Once most the iron had been consumed by the bacteria, free oxygen again started to seep into the ocean. This poisoned deep-water iron-eating bacteria throughout the world. The system flipped to a new steady state for the next few million years based around oxygen and silica.
A widely held theory is that following the mass die-off of bacteria, weathering of continental rocks and upwelling of iron from deep ocean volcanos replenished stocks, allowing the micro-organisms to return. Then the whole cycle would repeat over and over, first depositing rust, then a crash in microorganism numbers, followed by a recovery period when silica was deposited, then rust again and so on.
This is why you can see layers of silica and iron in the rock from Museum Victoria. These same patterns are found in rocks all over the world.
We build our society based on the world’s oldest rock formations made by wildlife
Some of the world’s oldest rock formations contain vast deposits of these iron bands, alternating with layers of silicon-based quartz. About 60% of mined iron ore reserves are thought to originate from this primordial process. Hence, almost our entire society since the iron-age has been built on this.
While we’re unlikely to return to a period of such instability in future, we aren’t immune to smaller fluctuations. Because of our size, sophistication and dependence on iron (which is naturally very scarce on an oxygen-rich planet) we need animals to collect it for us. And they need to make it biologically available for our cells.
We also need it to remain scarce, or else it upsets the oxygen part of the system. Which is why iron fertilisation plans are dangerous.
‘Our existence is balanced between having too much or too little of a good thing and, critically, it is wildlife that regulates this balance, and we evolved when things were just right.
Since the Great Oxidation Event 2.4 billion years ago, when iron was rusted into sediments and buried deep underground, biologically available iron (not the iron ore we dig out of the ground) has become so rare, it limits the magnitude of whole food chains. In the Antarctic, even in places where deep water resurfaces fast, photosynthetic microorganisms couldn’t rely solely on iron in the ocean.’
Wildlife in the Balance by Simon Mustoe
If you’d like to read more about why wildlife is essential to keeping our lives iron-rich, buy my book ‘Wildlife in the Balance.‘
