#fugacity

Mantle changes allowed oxygen to reach the air.

For the first couple of billion years of our world's history our planet was a pretty bleak and barren place. Life sole handhold on the Earth's rocky and watery skin consisted of extremophile bacteria until one of them managed to use a different chemical pathway to feed: photosynthesis. The culprits were cyanobacteria (aka blue green algae, covered at http://tinyurl.com/lmwmbry) and they eventually poisoned off most of the existing ecosystem, pushing it into increasingly niche habitats, where they remain today.

They did this by giving off free oxygen, which is normally very reactive and therefore binds quickly to other elements. The photo shows one of the consequences, marine banded iron formations from western Australia. As the molecule that made the world (as a recent book would have it) slowly spread the iron erupted in volcanic gases in the atmosphere and dissolved in the oceans bound to it and sank to the sea bottom. Once it was all used up, the molecule we all depend on for respiration started entering the air, where it slowly grew to its current 21%. This was the first of three main pulses of oxygenation known as the Great Oxygenation Event (GOE).

Research published in Nature last year suggests that the Earth made its own contribution to the process: there was an unexplained large decline in mantle melting that created ideal conditions for the event to happen. The team built a database of trace covering 70,000 samples of basalt in order to create a geochemical timeline of Earth's history, and discovered this mysterious drop that was roughly coincident with the GOE. They analysed the trace elements in the basalt and discovered that both the intensity and depth of mantle melting plummeted. They confirmed it using granites, formed from crustal melting, but with the heat energy often rising from the mantle.

Much of the world's iron comes from the weathering of volcanic rocks and erupted gases rich in iron. Melting got shallower and therefore the lavas and gases less iron rich, and combined with the decline in volcanism that followed that in melting, led to less iron dissolved in the air and oceans to soak life's molecule up, allowing oxygen to reach the atmosphere. The reductions in the iron contribution from volcanic gases are particularly important as they would have reacted with any oxygen as soon as it was released into the air. Their lowering made the chemical space for O2 to flourish.

This is the strongest empirical evidence yet for a connection between the depths of the Earth and the GOE, based on a statistical evidence of the preserved traces of deep geochemical activity in the rock record. Their evidence is more precise and detailed than any so far, allowing for better correlations to be reached with a greater degree of confidence. This is also the first hypothesis that answers the question of how did cyanobacteria overcome the chemical oxygen sinks in the seas and air in order to release free oxygen. The simple answer is that those sinks diminished, and by the time they increased again there was enough photosynthesis to absorb them all, and two billion years of built up sink had been reacted away into sea bottom forming the beautiful red rocks in the photo.

So there we have it, while the air we breathe was made useful for our kind of life by photosynthesis, it may be thanks to a change in the depths of the Earth that the oxygen we need established itself in the atmosphere. This led of course to the gradual evolution of oxygen respiring life, leading to where we are today, 2.5 billion years later.  

Loz

Image credit: Simon Poulton.

Nothing lasts forever, everything will end. Love, hate, life -even “dying” ends-.

A love dies, a new one is born, and then it dies and another one might come.

People change, people break hearts, people hurt and people heal.

Don’t get deeply attached, but do love deeply as long as it lasts.

Do your best, it will end anyway, but you would’ve given so much out of your conscious love, knowing each moment is precious because of its ephemerality: it won’t last.

Understand this and take off your shoulders that heavy weight you carry; you can’t control everything, you can’t force people to love you forever, to live forever, to be there forever. Be happy, be free. Enjoy and live. Let go and let in.

Fugacity.